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] Treasury Stock [Member] Common Class A [Member]	2007 Incentive Plan [Member] Treasury Stock [Member]	2007 Incentive Plan [Member]	The 2017 Equity and Incentive Compensation Plan [Member] Common Stock [Member] Common Class A [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, 2014							7,567,868	57,326,180		(1,578,554)	(4,814,716)
Balance at Dec. 31, 2014							$ 17,096	$ 486,317	$ (202,939)	$ (22,398)	$ (41,072)	$ (20,812)	$ 216,192
Net income									39,301				39,301
Adjustment to pension liability, net of income tax												3,528	3,528
Underwritten public offering (in shares)								13,511,040
Underwritten public offering								$ 167,313					$ 167,313
401(k) plan (in shares)								1,898					1,898
401(k) plan								$ 26					$ 26
Restricted stock awards (in shares)	287,513	150,308	(32,817)	(67,989)
Restricted stock awards			$ (287)	$ (818)	$ (1,105)
Share-based compensation							$ 2,229						4,019
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					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)
Share-based compensation							$ 2,439	$ 2,660					5,099
Repurchase of common stock (in shares)											(192,183)
Repurchase of common stock											$ (2,000)		(2,000)
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)
Underwritten public offering (in shares)								17,250,000
Underwritten public offering								$ 238,945					$ 238,945
401(k) plan (in shares)								1,224					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)
Share-based compensation							$ 2,880	$ 5,423					8,303
Repurchase of common stock (in shares)											(322,038)
Repurchase of common stock											$ (4,000)		(4,000)
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
Adoption of ASU 2016-09 excess tax benefit for stock-based compensation									$ 1,107				$ 1,107