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CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Noncontrolling Interest [Member]	Total
Beginning balance at Dec. 31, 2017	$ 512	$ 896,759	$ (13,253)	$ (479,170)	$ (26,692)		$ 378,156
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income				27,339			27,339
Tax benefit or Translation adjustment related to adoption of ASU (ASU 2014-09 [Member]) at Mar. 31, 2018				(134)			(134)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive income (loss), net of income taxes					78		78
Payment of dividend		167	(454)	(43,461)			(43,748)
Restricted stock units and stock options surrendered	1	(3,692)					(3,691)
Stock-based compensation expense		1,923					1,923
Ending balance at Mar. 31, 2018	513	895,157	(13,707)	(495,426)	(26,614)		359,923
Beginning balance at Dec. 31, 2017	512	896,759	(13,253)	(479,170)	(26,692)		378,156
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income							82,885
Ending balance at Jun. 30, 2018	513	897,185	(14,195)	(483,279)	(26,530)		373,694
Beginning balance at Mar. 31, 2018	513	895,157	(13,707)	(495,426)	(26,614)		359,923
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income				55,546			55,546
Other comprehensive income (loss), net of income taxes					84		84
Payment of dividend		102	(488)	(43,399)			(43,785)
Restricted stock units and stock options surrendered		(80)					(80)
Stock-based compensation expense		2,006					2,006
Ending balance at Jun. 30, 2018	513	897,185	(14,195)	(483,279)	(26,530)		373,694
Beginning balance at Dec. 31, 2018	513	900,795	(15,183)	(388,524)	(28,024)		469,577
Beginning balance at Dec. 31, 2018						$ 287,433	287,433
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income				29,408		(6,738)	29,408
Adjustment of noncontrolling interest to redemption value				(10,420)		10,420	(10,420)
Tax benefit or Translation adjustment related to adoption of ASU (ASU 2018-02 [Member]) at Mar. 31, 2019				2,707	(2,707)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive income (loss), net of income taxes					109		109
Payment of dividend		168	(504)	(46,076)			(46,412)
Restricted stock units and stock options surrendered	1	(3,825)					(3,824)
Stock-based compensation expense		2,026					2,026
Ending balance at Mar. 31, 2019	514	899,164	(15,687)	(412,905)	(30,622)		440,464
Ending balance at Mar. 31, 2019						291,115
Beginning balance at Dec. 31, 2018	513	900,795	(15,183)	(388,524)	(28,024)		469,577
Beginning balance at Dec. 31, 2018						287,433	287,433
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income							78,791
Tax benefit or Translation adjustment related to adoption of ASU (ASU 2018-02 [Member]) at Jun. 30, 2019							2,700
Tax benefit or Translation adjustment related to adoption of ASU at Jun. 30, 2019					(2,707)
Ending balance at Jun. 30, 2019	514	901,129	(15,687)	(420,408)	(30,524)		435,024
Ending balance at Jun. 30, 2019						287,718	287,718
Beginning balance at Mar. 31, 2019	514	899,164	(15,687)	(412,905)	(30,622)		440,464
Beginning balance at Mar. 31, 2019						291,115
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income				49,383		(3,099)	49,383
Adjustment of noncontrolling interest to redemption value				(10,293)		10,293	(10,293)
Tax benefit or Translation adjustment related to adoption of ASU (ASU 2018-02 [Member]) at Jun. 30, 2019							2,700
Tax benefit or Translation adjustment related to adoption of ASU at Jun. 30, 2019					(2,707)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive income (loss), net of income taxes					98		98
Payment of dividend		93		(46,593)			(46,500)
Distribution from consolidated joint venture						10,591
Restricted stock units and stock options surrendered		(63)					(63)
Stock-based compensation expense		1,935					1,935
Ending balance at Jun. 30, 2019	$ 514	$ 901,129	$ (15,687)	$ (420,408)	$ (30,524)		435,024
Ending balance at Jun. 30, 2019						$ 287,718	$ 287,718