Shareholders' equity - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 20,306	$ 20,146	$ 12,531
Total income tax benefit (provision)	4,297	4,354	(184)
Stock-based compensation net of tax	16,009	15,792	12,715
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	11,686	9,699	7,260
PSAs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	8,620	9,277	2,693
PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 0	$ 1,170	$ 2,578

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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