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
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share [Abstract]
Net income	$ 199,744	$ 152,400
Net income attributable to unvested awarded performance stock	(4,966)	(5,192)
Net income attributable to common shares	$ 194,778	$ 147,208
Weighted average number of common shares outstanding – basic	282,621	282,397
Less unvested awarded performance stock included in weighted average number of common shares outstanding – basic	(7,027)	(9,621)
Weighted average number of common shares outstanding for basic net income per common share	275,594	272,776
Dilutive effect of stock options	1,361	2,085
Weighted average number of shares outstanding – diluted	276,955	274,861
Basic (in dollars per share)	$ 0.71	$ 0.54
Diluted (in dollars per share)	$ 0.70	$ 0.54