Net Income Per Share - Reconciliation between Basic and Diluted Weighted Average Shares Outstanding (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net income	$ 92,593	$ 113,896	$ 73,922	$ 90,828	$ 206,489	$ 164,750
Net income attributable to unvested awarded performance stock	(3,020)		(1,618)		(6,273)	(3,529)
Net income attributable to common shares	$ 89,573		$ 72,304		$ 200,216	$ 161,221
Weighted average number of common shares outstanding - basic (in shares)	281,754		276,123		281,163	276,038
Less unvested awarded performance stock included in weighted average number of common shares outstanding - basic (in shares)	(9,191)		(6,042)		(8,542)	(5,912)
Weighted average number of common shares outstanding for basic earnings per common share (in shares)	272,563		270,081		272,621	270,126
Dilutive effect of stock options (in shares)	1,839		5,827		2,083	5,683
Weighted average number of shares outstanding - diluted (in shares)	274,402		275,908		274,704	275,809
Basic (in dollars per share)	$ 0.33		$ 0.27		$ 0.73	$ 0.60
Diluted (in dollars per share)	$ 0.33		$ 0.26		$ 0.73	$ 0.58