CONSOLIDATED STATEMENT OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Common Stock Class A Common Stock	Common Stock Class B Common Stock	Common Stock	Additional Paid In Capital. Class A Common Stock	Additional Paid In Capital.	Retained Earnings Class A Common Stock	Retained Earnings Class B Common Stock	Retained Earnings	Accumulated Other Comprehensive Income	Class A Common Stock	Class B Common Stock	Total
Balance at beginning of period at Dec. 31, 2015									$ 2,049
Increase (Decrease) in Stockholders' Equity
Net income												$ 35,903
Net change in accumulated other comprehensive income									925			925
Balance at end of period at Sep. 30, 2016									2,974
Balance at beginning of period at Dec. 31, 2015									2,049
Balance at end of period at Dec. 31, 2016			$ 4,906		$ 138,192			$ 460,621	687			604,406
Balance (in shares) at Dec. 31, 2016	18,615	2,245
Increase (Decrease) in Stockholders' Equity
Net income								40,794				40,794
Net change in accumulated other comprehensive income									808			808
Dividends declared Common Stock:
Dividends declared Common Stock						$ (12,082)	$ (1,324)			$ (12,082)	$ (1,324)
Stock options exercised, net of shares redeemed					33							33
Stock options exercised, net of shares redeemed (in shares)	2
Repurchase of Class A Common Stock			(2)		(121)			(435)				(558)
Repurchase of Class A Common Stock (in shares)	(13)
Conversion of Class B Common Stock to Class A Common Stock (in shares)	2	(2)
Net change in notes receivable on Class A Common Stock				$ 135						135
Deferred director compensation expense - Class A Common Stock				$ 147						$ 147
Deferred director compensation expense - Class A Common Stock (in shares)	5
Stock based compensation expense - performance stock units					364							364
Stock based compensation - restricted stock					373							373
Stock based compensation - restricted stock (in shares)	7
Stock based compensation expense - stock options					191							191
Balance at end of period at Sep. 30, 2017			$ 4,904		$ 139,314			$ 487,574	$ 1,495			$ 633,287
Balance (in shares) at Sep. 30, 2017	18,618	2,243