Net Income Per Share - Reconciliation between Basic and Diluted Weighted Average Shares Outstanding (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Abstract]
Net income	$ 146,354	$ 139,290	$ 199,744	$ 133,979	$ 96,784	$ 152,400	$ 485,387	$ 383,163
Net income attributable to unvested awarded performance stock	(3,069)			(3,740)			(10,901)	(12,634)
Net income attributable to common shares	$ 143,285			$ 130,239			$ 474,486	$ 370,529
Weighted average number of common shares outstanding – basic	282,132			283,426			282,177	283,139
Less unvested awarded performance stock included in weighted average number of common shares outstanding – basic	(5,917)			(7,911)			(6,337)	(9,336)
Weighted average number of common shares outstanding for basic net income per common share	276,215			275,515			275,840	273,803
Dilutive effect of potentially issuable common shares	1,338			1,418			1,306	1,535
Weighted average number of shares outstanding – diluted	277,553			276,933			277,146	275,338
Basic (in dollars per share)	$ 0.52			$ 0.47			$ 1.72	$ 1.35
Diluted (in dollars per share)	$ 0.52			$ 0.47			$ 1.71	$ 1.35