Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Common Stock [Member] Class A Common Stock [Member]	Common Stock [Member] Class B Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]
Balance at Dec. 31, 2015	$ 113,451	$ 0	$ 1	$ 0	$ 80,229	$ 29,570	$ 3,651
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification of capital structure	0	160	(1)	0	(159)
Common stock issuance, net of transaction costs	72,841	50			72,791
Stock-based compensation	492		0	0	492
Dividends declared and paid	(2,097)					(2,097)
Other comprehensive income (loss), net of income tax	(640)						(640)
Net income	26,167					26,167	0
Balance at Dec. 31, 2016	210,214	210	0	0	153,353	53,640	3,011
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock under stock-based compensation plan	1,077				1,077
Stock-based compensation	652				652
Dividends declared and paid	(5,039)					(5,039)
Other comprehensive income (loss), net of income tax	6,384						6,384
Net income	24,901					24,901
Balance at Dec. 31, 2017	238,189	210	0	0	155,082	73,502	9,395
Balance (Accounting Standards Update 2016-01 [Member]) at Dec. 31, 2017	238,189	210			155,082	79,992	2,905
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustment - unrealized gains on equity securities, net of tax | Accounting Standards Update 2016-01 [Member]	0					6,490	(6,490)
Reclassification of tax effect of TCJA	0
Reclassification of tax effect of TCJA | Accounting Standards Update 2018-02 [Member]	1,300					(1,308)	1,308
Issuance of stock under stock-based compensation plan	1,808	2			1,806
Stock-based compensation	1,597				1,597
Dividends declared and paid	(5,926)					(5,926)
Other comprehensive income (loss), net of income tax	(5,469)						(5,469)
Net income	33,787					33,787
Balance at Dec. 31, 2018	$ 263,986	$ 212	$ 0	$ 0	$ 158,485	$ 106,545	$ (1,256)