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				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Earnings Per Share [Abstract]
Net income	$ 139,290	$ 199,744	$ 96,784	$ 152,400	$ 339,033	$ 249,184
Net income attributable to unvested awarded performance stock	(3,010)		(3,580)		(7,876)	(8,855)
Net income attributable to common shares	$ 136,280		$ 93,204		$ 331,157	$ 240,329
Weighted average number of common shares outstanding – basic	281,784		283,591		282,200	282,994
Less unvested awarded performance stock included in weighted average number of common shares outstanding – basic	(6,090)		(10,491)		(6,556)	(10,056)
Weighted average number of common shares outstanding for basic net income per common share	275,694		273,100		275,644	272,938
Dilutive effect of potentially issuable common shares	1,183		1,262		1,270	1,581
Weighted average number of shares outstanding – diluted	276,877		274,362		276,914	274,519
Basic (in dollars per share)	$ 0.49		$ 0.34		$ 1.20	$ 0.88
Diluted (in dollars per share)	$ 0.49		$ 0.34		$ 1.20	$ 0.88