When a Whole Sentence Is in Parentheses, the Period Goes There, Too

That's both logical and customary.

If you're putting a whole sentence in parentheses, the custom follows logic—put the period inside the parentheses, not outside it. Thus, for an example from a court case (in a state, California, where citation sentences are often put in parentheses),

A two-step analysis is required when the superior court is requested to rule on a special motion to strike under the anti-SLAPP statutory framework. (Equilon Enterprises v. Consumer Cause, Inc. (2002) 29 Cal.4th 53, 67.)

The same thing with a more traditional English sentence would read,

A two-step analysis is required when the superior court is requested to rule on a special motion to strike under the anti-SLAPP statutory framework. (The California Supreme Court has taken this view since at least 2002.)

The following is not customary (focus on the last two characters):

A two-step analysis is required when the superior court is requested to rule on a special motion to strike under the anti-SLAPP statutory framework. (Equilon Enterprises v. Consumer Cause, Inc. (2002) 29 Cal.4th 53, 67).

In general, in the American styles to which I'm accustomed—especially legal style—the rule is that punctuation follows logic except (1) periods and commas (but not colons, semicolons, question marks, exclamation points, and other punctuation) generally go within quotation marks, even if they would logically go outside them, and (2) footnote references go after periods, commas, colons, and semicolons, even if they would logically go before them. (As you might gather, I'm speaking here descriptively, about the norms as I understand them, not about the norms as they should be.) I'm particularly confident about this with regard to California style for citations, but I think the norm is likely the same in other courts as well.

Just to make clear, the "logic" here is that, when the entire sentence is set off as a parenthetical, the period is part of the sentence and goes within the parentheses. On the other hand, if the parenthetical is just a clause within a sentence (whether the clause is a citation or plain English), then the period—or other punctuation—goes outside the parentheses, e.g.,

A two-step analysis is required when the superior court is requested to rule on a special motion to strike under the anti-SLAPP statutory framework (a view the California Supreme Court has taken since at least 2002).

Picayune, I realize, but helpful if you want to make your writing—especially legal writing—look especially tidy and professional.