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.	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, 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							45,632				45,632
Net change in accumulated other comprehensive income								(271)			(271)
Dividends declared on Common Stock:
Dividends declared on Common Stock					$ (16,158)	$ (1,773)			$ (16,158)	$ (1,773)
Stock options exercised, net of shares withheld				68							68
Stock options exercised, net of shares withheld (in shares)	4
Conversion of Class B Common Stock to Class A Common Stock (in shares)	2	(2)
Repurchase of Class A Common Stock			(4)	(422)			(622)				(1,048)
Repurchase of Class A Common Stock (in shares)	(26)
Net change in notes receivable on Class A Common Stock				235							235
Deferred director compensation expense - Class A Common Stock				191							191
Deferred director compensation expense - Class A Common Stock (in shares)	5
Stock-based awards, Performance stock units				491							491
Stock-based awards, Performance stock units (in shares)	7
Stock-based awards, Restricted stock				424							424
Stock-based awards, Stock options				227							227
Balance at end of period at Dec. 31, 2017			4,902	139,406			487,700	416			632,424
Balance (in shares) at Dec. 31, 2017	18,607	2,243
Increase (Decrease) in Stockholders' Equity
Adjustment for adoption							(35)	(338)			(373)
Net income							77,852				77,852
Net change in accumulated other comprehensive income								(1,075)			(1,075)
Dividends declared on Common Stock:
Dividends declared on Common Stock					(18,076)	(1,955)			(18,076)	(1,955)
Stock options exercised, net of shares withheld				83							83
Stock options exercised, net of shares withheld (in shares)	3
Conversion of Class B Common Stock to Class A Common Stock (in shares)	30	(30)
Repurchase of Class A Common Stock			(5)	(349)			(473)				(827)
Repurchase of Class A Common Stock (in shares)	(14)
Net change in notes receivable on Class A Common Stock				5							5
Deferred director compensation expense - Class A Common Stock			1	214							215
Deferred director compensation expense - Class A Common Stock (in shares)	5
Deferred designed key employee compensation expense - Class A Common Stock				430							430
Employee stock purchase plan - Class A Common Stock			2	228							230
Employee stock purchase plan - Class A Common Stock (in shares)	6
Stock-based awards, Performance stock units				106							106
Stock-based awards, Restricted stock				630							630
Stock-based awards, Restricted stock (in shares)	38
Stock-based awards, Stock options				265							265
Balance at end of period at Dec. 31, 2018			4,900	141,018			545,013	(997)			689,934
Balance (in shares) at Dec. 31, 2018	18,675	2,213
Increase (Decrease) in Stockholders' Equity
Adjustment for adoption							126				126
Net income							91,699				91,699
Net change in accumulated other comprehensive income								4,095			4,095
Dividends declared on Common Stock:
Dividends declared on Common Stock					$ (19,771)	$ (2,121)			$ (19,771)	$ (2,121)
Stock options exercised, net of shares withheld			11	(202)							(191)
Stock options exercised, net of shares withheld (in shares)	44
Conversion of Class B Common Stock to Class A Common Stock (in shares)	7	(7)
Repurchase of Class A Common Stock			(6)	(637)			(775)				(1,418)
Repurchase of Class A Common Stock (in shares)	(32)
Net change in notes receivable on Class A Common Stock				(222)							(222)
Deferred director compensation expense - Class A Common Stock				213							213
Deferred director compensation expense - Class A Common Stock (in shares)	6
Deferred designed key employee compensation expense - Class A Common Stock				371							371
Employee stock purchase plan - Class A Common Stock			2	492							494
Employee stock purchase plan - Class A Common Stock (in shares)	11
Stock-based awards, Performance stock units				(57)							(57)
Stock-based awards, Performance stock units (in shares)	23
Stock-based awards, Restricted stock				728							728
Stock-based awards, Restricted stock (in shares)	3
Stock-based awards, Stock options				364							364
Balance at end of period at Dec. 31, 2019			$ 4,907	$ 142,068			$ 614,171	$ 3,098			$ 764,244
Balance (in shares) at Dec. 31, 2019	18,737	2,206