Condensed Consolidated Statement of Stockholders' Equity (Unaudited) - 3 months ended Mar. 31, 2018 - USD ($) $ in Thousands	Common Stock [Member] Common Class A [Member]	Common Stock [Member]	Retained Earnings [Member]	Treasury Stock [Member] Common Class A [Member]	Treasury Stock [Member]	AOCI Attributable to Parent [Member]	Total
Balance (in shares) at Dec. 31, 2017	8,349,069	88,788,664		(1,750,692)	(5,535,076)
Balance at Dec. 31, 2017	$ 24,644	$ 902,518	$ 161,694	$ (24,232)	$ (49,562)	$ (22,165)	$ 992,897
Net income			19,945				19,945
Restricted stock awards (in shares)	220,080	318,196		(89,422)	(107,456)
Restricted stock awards				$ (1,252)	$ (1,757)		(3,009)
Restricted stock unit awards (in shares)		209,500			(82,201)
Restricted stock unit awards					$ (1,344)		(1,344)
Repurchase of common stock (in shares)					(1,551,710)
Repurchase of common stock					$ (19,607)		(19,607)
Share-based compensation	$ 505	$ 1,652					2,157
Balance (in shares) at Mar. 31, 2018	8,569,149	89,316,360		(1,840,114)	(7,276,443)
Balance at Mar. 31, 2018	$ 25,149	$ 904,170	$ 181,639	$ (25,484)	$ (72,270)	$ (22,165)	$ 991,039