Consolidated Statement of Stockholders' Equity - USD ($) $ in Thousands	2007 Incentive Plan [Member] Common Stock [Member] Common Class A [Member]	2007 Incentive Plan [Member] Common Stock [Member]	2007 Incentive Plan [Member] Retained Earnings [Member]	2007 Incentive Plan [Member] Treasury Stock [Member] Common Class A [Member]	2007 Incentive Plan [Member] Treasury Stock [Member]	2007 Incentive Plan [Member] AOCI Attributable to Parent [Member]	2007 Incentive Plan [Member]	The 2017 Equity and Incentive Compensation Plan [Member] Common Stock [Member] Common Class A [Member]	The 2017 Equity and Incentive Compensation Plan [Member] Common Stock [Member]	The 2017 Equity and Incentive Compensation Plan [Member] Treasury Stock [Member] Common Class A [Member]	The 2017 Equity and Incentive Compensation Plan [Member] Treasury Stock [Member]	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, 2015												7,855,381	70,989,426		(1,611,371)	(4,882,705)
Balance at Dec. 31, 2015												$ 19,325	$ 655,446	$ (163,638)	$ (22,685)	$ (41,890)	$ (17,284)	$ 429,274
Net income														62,273				62,273
Adjustment to pension liability, net of income tax																	(361)	(361)
401(k) plan (in shares)													2,571
401(k) plan													$ 29					29
Restricted stock awards (in shares)	218,612	237,500		(57,760)	(60,518)
Restricted stock awards				$ (655)	$ (798)		$ (1,453)
Repurchase of common stock (in shares)																(192,183)
Repurchase of common stock																$ (2,000)		(2,000)
Share-based compensation (in shares)
Share-based compensation												$ 2,439	$ 2,660					5,099
Balance (in shares) at Dec. 31, 2016												8,073,993	71,229,497		(1,669,131)	(5,135,406)
Balance at Dec. 31, 2016												$ 21,764	$ 658,135	(101,365)	$ (23,340)	$ (44,688)	(17,645)	492,861
Net income														261,952				261,952
Adjustment to pension liability, net of income tax																	(4,520)	(4,520)
401(k) plan (in shares)													1,224
401(k) plan													$ 15					15
Restricted stock awards (in shares)	198,220	307,943		(81,561)	(77,632)			76,856
Restricted stock awards				$ (892)	$ (874)		$ (1,766)
Repurchase of common stock (in shares)																(322,038)
Repurchase of common stock																$ (4,000)		(4,000)
Share-based compensation												2,880	5,423					8,303
Adoption of ASU 2016-09 excess tax benefit for stock-based compensation														1,107				1,107
Underwritten public offering (in shares)													17,250,000
Underwritten public offering													$ 238,945					238,945
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														210,803				210,803
Adjustment to pension liability, net of income tax																	788	788
Restricted stock awards (in shares)												220,080	391,836		(89,422)	(107,456)
Restricted stock awards															$ (1,252)	$ (1,757)		(3,009)
Repurchase of common stock (in shares)																(1,551,710)
Repurchase of common stock																$ (19,607)		(19,607)
Share-based compensation (in shares)
Share-based compensation												$ 2,042	$ 5,147					7,189
Restricted stock unit awards (in shares)													209,500			(82,201)
Restricted stock unit awards																$ (1,344)		(1,344)
Forefiture of restricted stock awards (in shares)													(91,057)
Forefiture of restricted stock awards													$ (528)					(528)
Balance (in shares) at Dec. 31, 2018												8,569,149	89,298,943		(1,840,114)	(7,276,443)
Balance at Dec. 31, 2018												$ 26,686	$ 907,137	$ 372,497	$ (25,484)	$ (72,270)	$ (21,377)	$ 1,187,189