Earnings Per Share (Details) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Jun. 17, 2020 $ / shares shares	Aug. 12, 2016 $ / shares
Earnings Per Share Reconciliation [Abstract]
Net income (loss) | $	$ (764,614)	$ (187,001)	$ 508,407
Basic weighted-average common shares outstanding	113,730	112,544	111,912
Dilutive effect of non-vested RSUs and contingent PSUs	0	0	1,590
Diluted weighted-average common shares outstanding	113,730	112,544	113,502
Basic net income (loss) per common share | $ / shares	$ (6.72)	$ (1.66)	$ 4.54
Diluted net income (loss) per common share | $ / shares	$ (6.72)	$ (1.66)	$ 4.48
Class of Warrant or Right, Number of Securities Called by Warrants or Rights				5,900
Exercise price of warrants | $ / shares				$ 0.01
Incremental Common Shares Attributable to Dilutive Effect of Warrants	0
Anti-dilutive shares excluded from earnings per share	265	684	0
1.50% Senior Unsecured Convertible Notes Due 2021 [Member]
Earnings Per Share Reconciliation [Abstract]
Capped Call, Cap Price | $ / shares					$ 60.00
Performance Shares (PSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Multiplier applied to PSU awards at settlement	0.9	0	0
Minimum [Member] | Performance Shares (PSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Multiplier applied to PSU awards at settlement	0
Maximum [Member] | Performance Shares (PSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Multiplier applied to PSU awards at settlement	2