Summary of Significant Accounting Policies - Reconciliation between Basic and Diluted Weighted Average Shares Outstanding (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Net income	$ 97,320	$ 133,979	$ 96,784	$ 152,400	$ 76,519	$ 115,506	$ 92,593	$ 113,896	$ 480,483	$ 398,514	$ 344,255
Net income attributable to unvested awarded performance stock									(15,197)	(12,873)	(8,297)
Net income attributable to common shares									$ 465,286	$ 385,641	$ 335,958
Weighted average number of common shares outstanding – basic									283,294	281,566	277,663
Less unvested awarded performance stock included in weighted average number of common shares outstanding – basic									(8,960)	(9,095)	(6,692)
Weighted average number of common shares outstanding for basic earnings per common share									274,334	272,471	270,971
Dilutive effect of stock options									1,533	2,145	4,550
Weighted average number of shares outstanding – diluted									275,867	274,616	275,521
Net income per share:
Basic (in dollars per share)	$ 0.34	$ 0.47	$ 0.34	$ 0.54	$ 0.27	$ 0.41	$ 0.33	$ 0.41	$ 1.70	$ 1.42	$ 1.24
Diluted (in dollars per share)	$ 0.34	$ 0.47	$ 0.34	$ 0.54	$ 0.27	$ 0.41	$ 0.33	$ 0.40	$ 1.69	$ 1.40	$ 1.22