CONSOLIDATED STATEMENTS OF EQUITY - USD ($)	Total	Common Stock	Additional Paid-in Capital	Treasury Stock	Retained Earnings	Noncontrolling Interest	Stock Options	Stock Options Additional Paid-in Capital	Stock Options Treasury Stock	Former Affiliated Entity Stock Options	Former Affiliated Entity Stock Options Additional Paid-in Capital	Former Affiliated Entity Stock Options Treasury Stock
Beginning Balances at Dec. 31, 2014	$ 709,742,000	$ 36,947,000	$ 558,945,000	$ (55,691,000)	$ 167,001,000	$ 2,540,000
Beginning Balances, Shares at Dec. 31, 2014		36,946,603		(3,485,278)
Net income	(212,371,000)				(213,047,000)	676,000
Distributions to noncontrolling interest	(701,000)					(701,000)
Issuances of common stock, Shares				335,611
Issuances of common stock, Value			(5,362,000)	$ 5,362,000
Issuances from exercises of stock options, net of swaps, Shares												3,999
Issuances from exercises of stock options, net of swaps, Value										$ 31,000	$ (33,000)	$ 64,000
Shares withheld for payroll taxes, Shares				(51,521)
Shares withheld for payroll taxes, Value	(762,000)		(1,000)	$ (761,000)
Forfeitures of restricted stock, Shares				(6,579)
Forfeitures of restricted stock, Value	0		125,000	$ (125,000)
Share-based compensation	8,576,000		8,576,000
Tax benefit from exercise of restricted stock units and stock options and vested restricted stock	(400,000)		(400,000)
Ending Balances at Dec. 31, 2015	504,115,000	$ 36,947,000	561,850,000	$ (51,151,000)	(46,046,000)	2,515,000
Ending Balances, Shares at Dec. 31, 2015		36,946,603		(3,203,768)
Net income	60,179,000				58,648,000	1,531,000
Distributions to noncontrolling interest	(2,579,000)					(2,579,000)
Issuances of common stock, Shares				288,397
Issuances of common stock, Value	$ 0		(4,570,000)	$ 4,570,000
Issuances from exercises of stock options, net of swaps, Shares									35,406
Issuances from exercises of stock options, net of swaps, Value							$ 328,000	$ (224,000)	$ 552,000
Shares withheld for payroll taxes, Shares	(25,082)			(23,312)
Shares withheld for payroll taxes, Value	$ (222,000)		(28,000)	$ (194,000)
Shares repurchased, Shares	(283,976)			(283,976)
Shares repurchased, Value	$ (3,537,000)			$ (3,537,000)
Share-based compensation	4,045,000		4,045,000
Settlement of tangible equity units, Shares		7,857,000
Settlement of tangible equity units, Value		$ 7,857,000	(7,857,000)
Reacquisition of equity component related to convertible debt	(211,000)		(211,000)
Ending Balances at Dec. 31, 2016	562,118,000	$ 44,804,000	553,005,000	$ (49,760,000)	12,602,000	1,467,000
Ending Balances, Shares at Dec. 31, 2016		44,803,603		(3,187,253)
Net income	52,332,000				50,254,000	2,078,000
Distributions to noncontrolling interest	(2,125,000)					(2,125,000)
Issuances of common stock, Shares				335,261
Issuances of common stock, Value	$ 0		(5,224,000)	$ 5,224,000
Issuances from exercises of stock options, net of swaps, Shares							768,000		63,195
Issuances from exercises of stock options, net of swaps, Value							$ 616,000	$ (367,000)	$ 983,000
Shares withheld for payroll taxes, Shares	(75,870)			(75,870)
Shares withheld for payroll taxes, Value	$ (981,000)		0	$ (981,000)
Shares repurchased, Shares				2,864,667
Shares repurchased, Value	0	$ (2,864,667)	(35,109,000)	$ 44,534,000	(6,560,000)
Share-based compensation	6,458,000		6,458,000
Settlement of tangible equity units, Shares		0
Settlement of tangible equity units, Value	(12,786,000)	$ 0	(12,786,000)
Ending Balances at Dec. 31, 2017	$ 605,632,000	$ 41,939,000	$ 505,977,000	$ 0	$ 56,296,000	$ 1,420,000
Ending Balances, Shares at Dec. 31, 2017		41,938,936		0