Shareholders' equity - Earnings Per Share (Basic and Diluted) (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Net income	$ 482,763	$ 286,235	$ 401,340
Income from discontinued operations, net of tax	0	0	4,325
Net loss attributable to redeemable noncontrolling interest	15	0	0
Accretion of redeemable noncontrolling interest	(933)	0	0
Adjustment of redeemable noncontrolling interest to redemption value	(15)	0	0
Earnings available to common shareholders	$ 481,830	$ 286,235	$ 405,665
Weighted average number of common shares outstanding - basic	219,232	217,138	216,184
Effect of dilutive securities
Weighted average number of common shares outstanding - diluted	219,733	217,977	216,621
Earnings from continuing operations per share - basic (in dollars per share)	$ 2.20	$ 1.32	$ 1.86
Earnings from discontinued operations per share - basic (in dollars per share)	0	0	0.02
Net income per share - basic (in dollars per share)	2.20	1.32	1.88
Earnings from continuing operations per share - diluted (in dollars per share)	2.19	1.31	1.85
Earnings from discontinued operations per share - diluted (in dollars per share)	0	0	0.02
Net income per share - diluted (in dollars per share)	$ 2.19	$ 1.31	$ 1.87
Restricted Stock
Effect of dilutive securities
Effect of dilutive securities (in shares)	246	461	139
Performance Shares
Effect of dilutive securities
Effect of dilutive securities (in shares)	254	346	97
Stock Options
Effect of dilutive securities
Effect of dilutive securities (in shares)	1	32	201