Condensed Consolidated Statements of Equity (unaudited) - USD ($) $ in Thousands	Total	Common Stock	Common Stock - Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Beginning Balance (in shares) at Dec. 31, 2017		38,837,749
Beginning Balance at Dec. 31, 2017	$ 567,582	$ 5	$ 515,452	$ 134,928	$ 278	$ (83,081)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of restricted stock units to common stock (net of shares of treasury stock purchased) (in shares)		127,470
Conversion of restricted stock units to common stock (net of shares of treasury stock purchased)	(621)					(621)
Settlement of stock appreciation rights in common stock (net of shares of treasury stock purchased) (in shares)		33,463
Settlement of stock appreciation rights in common stock (net of shares of treasury stock purchased)	(172)					(172)
Partial termination of capped call options (in shares)		(15,012)
Termination of capped call options	85		252			(167)
Convertible debt extinguishment impact (net of tax impact)	(440)		(440)
Treasury stock purchases (in shares)		(641,601)
Treasury stock purchases	(7,828)					(7,828)
Stock compensation expense	1,794		1,794
Other comprehensive income (loss)	719				719
Net income (loss)	214,389			214,389
Ending Balance (in shares) at Mar. 31, 2018		38,342,069
Ending Balance at Mar. 31, 2018	775,508	$ 5	517,058	349,317	997	(91,869)
Beginning Balance (in shares) at Dec. 31, 2017		38,837,749
Beginning Balance at Dec. 31, 2017	567,582	$ 5	515,452	134,928	278	(83,081)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Settlement of 2019 Convertible Senior Notes conversion premium	0
Net income (loss)	273,242
Ending Balance (in shares) at Sep. 30, 2018		37,299,704
Ending Balance at Sep. 30, 2018	782,095	$ 5	486,618	408,170	(1,195)	(111,503)
Beginning Balance (in shares) at Mar. 31, 2018		38,342,069
Beginning Balance at Mar. 31, 2018	775,508	$ 5	517,058	349,317	997	(91,869)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of restricted stock units to common stock (net of shares of treasury stock purchased) (in shares)		149,362
Conversion of restricted stock units to common stock (net of shares of treasury stock purchased)	(1,516)					(1,516)
Settlement of stock appreciation rights in common stock (net of shares of treasury stock purchased) (in shares)		63,549
Settlement of stock appreciation rights in common stock (net of shares of treasury stock purchased)	(580)		(95)			(485)
Convertible debt extinguishment impact (net of tax impact)	(23,634)		(23,634)
Treasury stock purchases (in shares)		(1,296,243)
Treasury stock purchases	(17,220)					(17,220)
Stock compensation expense	2,203		2,203
Other comprehensive income (loss)	(1,823)				(1,823)
Net income (loss)	33,850			33,850
Ending Balance (in shares) at Jun. 30, 2018		37,258,737
Ending Balance at Jun. 30, 2018	766,788	$ 5	495,532	383,167	(826)	(111,090)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of restricted stock units to common stock (net of shares of treasury stock purchased) (in shares)		13,301
Conversion of restricted stock units to common stock (net of shares of treasury stock purchased)	(88)					(88)
Settlement of stock appreciation rights in common stock (net of shares of treasury stock purchased) (in shares)		27,666
Settlement of stock appreciation rights in common stock (net of shares of treasury stock purchased)	(434)		(109)			(325)
Convertible debt extinguishment impact (net of tax impact)	(10,032)		(10,032)
Stock compensation expense	1,227		1,227
Other comprehensive income (loss)	(369)				(369)
Net income (loss)	25,003			25,003
Ending Balance (in shares) at Sep. 30, 2018		37,299,704
Ending Balance at Sep. 30, 2018	782,095	$ 5	486,618	408,170	(1,195)	(111,503)
Beginning Balance (in shares) at Dec. 31, 2018		37,318,942
Beginning Balance at Dec. 31, 2018	765,253	$ 5	451,427	427,244	(1,656)	(111,767)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of restricted stock units to common stock (net of shares of treasury stock purchased) (in shares)		283,339
Conversion of restricted stock units to common stock (net of shares of treasury stock purchased)	(2,760)					(2,760)
Settlement of stock appreciation rights in common stock (net of shares of treasury stock purchased) (in shares)		16,937
Settlement of stock appreciation rights in common stock (net of shares of treasury stock purchased)	(171)		(12)			(159)
Partial termination of capped call options (in shares)		(1,087)
Termination of capped call options	0		30			(30)
Convertible debt extinguishment impact (net of tax impact)	(152)		(152)
Stock compensation expense	1,353		1,353
Other comprehensive income (loss)	(362)				(362)
Net income (loss)	(43,404)			(43,404)
Ending Balance (in shares) at Mar. 31, 2019		37,618,131
Ending Balance at Mar. 31, 2019	713,241	$ 5	452,646	377,324	(2,018)	(114,716)
Beginning Balance (in shares) at Dec. 31, 2018		37,318,942
Beginning Balance at Dec. 31, 2018	765,253	$ 5	451,427	427,244	(1,656)	(111,767)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Settlement of 2019 Convertible Senior Notes conversion premium	(18,779)
Net income (loss)	(121,447)
Ending Balance (in shares) at Sep. 30, 2019		38,964,276
Ending Balance at Sep. 30, 2019	637,618	$ 5	446,435	299,281	(2,640)	(105,463)
Beginning Balance (in shares) at Mar. 31, 2019		37,618,131
Beginning Balance at Mar. 31, 2019	713,241	$ 5	452,646	377,324	(2,018)	(114,716)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of restricted stock units to common stock (net of shares of treasury stock purchased) (in shares)		58,759
Conversion of restricted stock units to common stock (net of shares of treasury stock purchased)	(518)					(518)
Settlement of stock appreciation rights in common stock (net of shares of treasury stock purchased) (in shares)		4,631
Settlement of stock appreciation rights in common stock (net of shares of treasury stock purchased)	(24)		(7)			(17)
Settlement of 2019 Convertible Senior Notes conversion premium (in shares)		1,902,781
Settlement of 2019 Convertible Senior Notes conversion premium	0		(18,779)			18,779
Termination of capped call options (in shares)		(625,558)
Termination of capped call options	0		8,952			(8,952)
Stock compensation expense	1,824		1,824
Other comprehensive income (loss)	395				395
Net income (loss)	(62,097)			(62,097)
Ending Balance (in shares) at Jun. 30, 2019		38,958,744
Ending Balance at Jun. 30, 2019	652,821	$ 5	444,636	315,227	(1,623)	(105,424)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of restricted stock units to common stock (net of shares of treasury stock purchased) (in shares)		3,557
Conversion of restricted stock units to common stock (net of shares of treasury stock purchased)	(39)					(39)
Settlement of stock appreciation rights in common stock (net of shares of treasury stock purchased) (in shares)		1,975
Settlement of stock appreciation rights in common stock (net of shares of treasury stock purchased)	$ (5)		(5)			0
Termination of capped call options (in shares)	625,558
Stock compensation expense	$ 1,804		1,804
Other comprehensive income (loss)	(1,017)				(1,017)
Net income (loss)	(15,946)			(15,946)
Ending Balance (in shares) at Sep. 30, 2019		38,964,276
Ending Balance at Sep. 30, 2019	$ 637,618	$ 5	$ 446,435	$ 299,281	$ (2,640)	$ (105,463)