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
Increase (Decrease) in Stockholders' Equity
Adjustment for adoption							$ 126				$ 126
Balance at beginning 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
Net income							47,523				47,523
Net change in accumulated other comprehensive income								4,259			4,259
Dividends declared on Common Stock:
Dividends declared on Common Stock					$ (9,865)	$ (1,061)			$ (9,865)	$ (1,061)
Stock options exercised, net of shares withheld			8	(110)							(102)
Stock options exercised, net of shares withheld (in shares)	34
Conversion of Class B Common Stock to Class A Common Stock			(1)	(376)			(2)				(379)
Conversion of Class B Common Stock to Class A Common Stock (in shares)	(8)
Repurchase of Class A Common Stock		$ (5)
Repurchase of Class A Common Stock (in shares)	5
Net change in notes receivable on Class A Common Stock				(192)							(192)
Deferred director compensation expense - Class A Common Stock				106							106
Deferred director compensation expense - Class A Common Stock (in shares)	5
Deferred designed key employee compensation expense - Class A Common Stock				226							226
Employee stock purchase plan - Class A Common Stock				235							235
Employee stock purchase plan - Class A Common Stock (in shares)	5
Stock-based awards, Performance stock units				(57)							(57)
Stock-based awards, Performance stock units (in shares)	23
Stock-based awards, Restricted stock				475							475
Stock-based awards, Restricted stock (in shares)	1
Stock-based awards, Stock options				200							200
Balance at end of period at Jun. 30, 2019			4,907	141,525			581,734	3,262			731,428
Balance (in shares) at Jun. 30, 2019	18,740	2,208
Balance at beginning of period at Mar. 31, 2019			4,899	141,206			569,189	1,797			717,091
Balance (in shares) at Mar. 31, 2019	18,698	2,213
Increase (Decrease) in Stockholders' Equity
Net income							18,007				18,007
Net change in accumulated other comprehensive income								1,465			1,465
Dividends declared on Common Stock:
Dividends declared on Common Stock					(4,932)	(530)			(4,932)	(530)
Stock options exercised, net of shares withheld			8	(110)							(102)
Stock options exercised, net of shares withheld (in shares)	34
Repurchase of Class A Common Stock (in shares)	5	(5)
Net change in notes receivable on Class A Common Stock				(158)							(158)
Deferred director compensation expense - Class A Common Stock				41							41
Deferred designed key employee compensation expense - Class A Common Stock				58							58
Employee stock purchase plan - Class A Common Stock				114							114
Employee stock purchase plan - Class A Common Stock (in shares)	2
Stock-based awards, Restricted stock				295							295
Stock-based awards, Restricted stock (in shares)	1
Stock-based awards, Stock options				79							79
Balance at end of period at Jun. 30, 2019			4,907	141,525			581,734	3,262			731,428
Balance (in shares) at Jun. 30, 2019	18,740	2,208
Increase (Decrease) in Stockholders' Equity
Adjustment for adoption							(4,291)				(4,291)
Balance at beginning 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
Increase (Decrease) in Stockholders' Equity
Net income							42,501				42,501
Net change in accumulated other comprehensive income								6,528			6,528
Dividends declared on Common Stock:
Dividends declared on Common Stock					(10,705)	(1,144)			(10,705)	(1,144)
Stock options exercised, net of shares withheld			8	248							256
Stock options exercised, net of shares withheld (in shares)	19
Conversion of Class B Common Stock to Class A Common Stock (in shares)	6	(6)
Repurchase of Class A Common Stock			(20)	(582)			(2,250)				(2,852)
Repurchase of Class A Common Stock (in shares)	(86)
Net change in notes receivable on Class A Common Stock				114							114
Deferred director compensation expense - Class A Common Stock				150							150
Deferred director compensation expense - Class A Common Stock (in shares)	4
Deferred designed key employee compensation expense - Class A Common Stock				277							277
Employee stock purchase plan - Class A Common Stock			2	289							291
Employee stock purchase plan - Class A Common Stock (in shares)	9
Stock-based awards, Performance stock units				(200)							(200)
Stock-based awards, Performance stock units (in shares)	18
Stock-based awards, Restricted stock			1	247							248
Stock-based awards, Restricted stock (in shares)	1
Stock-based awards, Stock options				202							202
Balance at end of period at Jun. 30, 2020			4,898	142,813			638,282	9,626			795,619
Balance (in shares) at Jun. 30, 2020	18,708	2,200
Balance at beginning of period at Mar. 31, 2020			4,890	141,928			628,397	8,831			784,046
Balance (in shares) at Mar. 31, 2020	18,687	2,200
Increase (Decrease) in Stockholders' Equity
Net income							15,804				15,804
Net change in accumulated other comprehensive income								795			795
Dividends declared on Common Stock:
Dividends declared on Common Stock					$ (5,347)	$ (572)			$ (5,347)	$ (572)
Stock options exercised, net of shares withheld			7	291							298
Stock options exercised, net of shares withheld (in shares)	17
Net change in notes receivable on Class A Common Stock				84							84
Deferred director compensation expense - Class A Common Stock				71							71
Deferred designed key employee compensation expense - Class A Common Stock				134							134
Employee stock purchase plan - Class A Common Stock			1	135							136
Employee stock purchase plan - Class A Common Stock (in shares)	4
Stock-based awards, Restricted stock				60							60
Stock-based awards, Stock options				110							110
Balance at end of period at Jun. 30, 2020			$ 4,898	$ 142,813			$ 638,282	$ 9,626			$ 795,619
Balance (in shares) at Jun. 30, 2020	18,708	2,200