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, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Net income	$ 133,979	$ 96,784	$ 152,400	$ 115,506	$ 92,593	$ 113,896	$ 383,163	$ 321,995
Net income attributable to unvested awarded performance stock	(3,740)			(3,772)			(12,634)	(10,386)
Net income attributable to common shares	$ 130,239			$ 111,734			$ 370,529	$ 311,609
Weighted average number of common shares outstanding – basic	283,426			282,178			283,139	281,505
Less unvested awarded performance stock included in weighted average number of common shares outstanding – basic	(7,911)			(9,216)			(9,336)	(9,080)
Weighted average number of common shares outstanding for basic net income per common share	275,515			272,962			273,803	272,425
Dilutive effect of stock options	1,418			2,113			1,535	2,104
Weighted average number of shares outstanding – diluted	276,933			275,075			275,338	274,529
Basic (in dollars per share)	$ 0.47			$ 0.41			$ 1.35	$ 1.14
Diluted (in dollars per share)	$ 0.47			$ 0.41			$ 1.35	$ 1.14