CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Class A [Member]	Common Class B [Member]	Additional Paid In Capital [Member]	Retained Earnings [Member]
Opening Balance SHARES at Dec. 31, 2015		32,480,551	7,197,532
Compensation expense related to granting of restricted stock awards SHARES		1,095,759	0
Issuance of common stock related to an incentive plan SHARES		31,933	0
Exercise of stock options SHARES		134,238	0
Purchase of vested employee restricted stock units SHARES		(232,297)	0
Ending Balance SHARES at Dec. 31, 2016		33,510,184	7,197,532
Opening Balance VALUE at Dec. 31, 2015	$ 361,450	$ 325	$ 72	$ 611,754	$ (250,701)
Net income (loss)	38,065	0	0	0	38,065
Compensation expense related to granting of restricted stock awards VALUE	6,539	11	0	6,528	0
Issuance of common stock related to an incentive plan VALUE	379	0	0	379	0
Purchase of vested employee restricted stock units	(2,268)	(2)	0	(2,266)	0
Payments of dividends VALUE	(8,666)	0	0	(8,666)	0
Realization of tax benefit for dividend equivalent payments VALUE					0
Exercise of stock options VALUE	265	1	0	264	0
Preferred stock dividend	(1,788)	0	0	(1,788)	0
Dividend equivalents, net of forfeitures	(602)	0	0	(602)	0
Ending Balance VALUE at Dec. 31, 2016	$ 393,374	$ 335	$ 72	605,603	(212,636)
Compensation expense related to granting of stock options SHARES	0
Compensation expense related to granting of restricted stock awards SHARES		183,980	0
Issuance of common stock related to an incentive plan SHARES		14,833	0
Exercise of stock options SHARES	6,500	6,500	0
Purchase of vested employee restricted stock units SHARES		(167,620)	0
Ending Balance SHARES at Sep. 30, 2017		33,547,877	7,197,532
Net income (loss)	$ 1,184	$ 0	$ 0	0	1,184
Compensation expense related to granting of restricted stock awards VALUE	4,629	2	0	4,627	0
Issuance of common stock related to an incentive plan VALUE	182	0	0	182	0
Purchase of vested employee restricted stock units	(2,546)	(2)	0	(2,544)	0
Payments of dividends VALUE	(16,659)	0	0	(16,659)	0
Forfeitures of dividend equivalents VALUE	(591)	0	0	(591)	0
Exercise of stock options VALUE	22	0	0	22	0
Preferred stock dividend	(1,650)	0	0	(1,650)	0
Ending Balance VALUE at Sep. 30, 2017	$ 383,057	$ 335	$ 72	$ 589,524	$ (206,874)