Earnings Per Share (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
Earnings Per Share [Abstract]
Net earnings (loss)	$ 116,830	$ 45,503	$ 33,204	$ (1,433,111)	$ 117,881	$ 110,026	$ 128,125	$ 112,604	$ (1,237,574)	$ 468,636	$ 465,339
Undistributed Earnings (Loss) Allocated to Participating Securities, Basic									(1,782)	(5,182)	(5,119)
Net Income (Loss) Available to Common Stockholders, Basic									$ (1,239,356)	$ 463,454	$ 460,220
Weighted-average basic shares and unvested restricted stock outstanding									118,463	120,468	125,100
Less: weighted-average unvested restricted stock outstanding									(1,610)	(1,502)	(1,460)
Weighted-average basic shares outstanding									116,853	118,966	123,640
Earnings Per Share, Basic (usd per share)	$ 0.99	$ 0.38	$ 0.28	$ (12.23)	$ 0.98		$ 1.07	$ 0.92	$ (10.61)	$ 3.90	$ 3.72
Net earnings (loss) allocated to common shares									$ (1,239,356)	$ 463,454	$ 460,220
Diluted income per share (usd per share)	$ 0.99	$ 0.38	$ 0.28	$ (12.23)	$ 0.98	$ 0.92	$ 1.07	$ 0.92	$ (10.61)	$ 3.90	$ 3.72