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	Noncontrolling Interest
Beginning Balance (in shares) at Dec. 31, 2016		38,553,413
Beginning Balance at Dec. 31, 2016	$ 610,174	$ 5	$ 480,906	$ 214,007	$ (5,751)	$ (81,824)	$ 2,831
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of restricted stock units to common stock (net of shares of treasury stock purchased) (in shares)		131,893
Conversion of restricted stock units to common stock (net of shares of treasury stock purchased)	(638)					(638)
Acquisition of noncontrolling interest	(3,102)		(271)				(2,831)
Stock compensation expense	2,996		2,996
Other comprehensive income	3,181				3,181		0
Net income (loss)	(50,723)			(50,723)			0
Ending Balance (in shares) at Jun. 30, 2017		38,685,306
Ending Balance at Jun. 30, 2017	561,888	$ 5	483,631	163,284	(2,570)	(82,462)	0
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)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of restricted stock units to common stock (net of shares of treasury stock purchased) (in shares)		276,832
Conversion of restricted stock units to common stock (net of shares of treasury stock purchased)	(2,137)					(2,137)
Settlement of stock appreciation rights in common stock (net of shares of treasury stock purchased) (in shares)		97,012
Settlement of stock appreciation rights in common stock (net of shares of treasury stock purchased)	(752)					(657)
Partial termination of capped call options (in shares)		(15,012)
Partial termination of capped call options	85		252			(167)
Convertible debt extinguishment impact (net of tax impact)	(24,074)		(24,074)
Treasury stock purchases (in shares)		(1,937,844)
Treasury stock purchases	(25,048)					(25,048)
Stock compensation expense	3,997		3,997
Other comprehensive income	(1,104)				(1,104)
Net income (loss)	248,239			248,239
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)	$ 0