Consolidated Statements of Stockholders' Equity - Unaudited - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Preferred Stock	Common Stock	Additional Paid-in Capital	Additional Paid-in Capital Cumulative Effect, Period of Adoption, Adjustment	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) Cumulative Effect, Period of Adoption, Adjustment
Beginning balance (in shares) at Dec. 31, 2018			1,200,000	45,074,322
Beginning balance at Dec. 31, 2018	$ 490,336		$ 12	$ 451	$ 454,512		$ 38,371		$ (3,010)
Beginning balance (Adoption of ASU 2016-01) at Dec. 31, 2018		$ 0						$ (69)		$ 69
Beginning balance (Adoption of ASU 2018-07) at Dec. 31, 2018		$ 0				$ 2,159		$ (2,159)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	29,173						29,173
Change in unrealized appreciation on available-for-sale securities	20,842								20,842
Issuance of shares (in shares)				6,851,213
Issuance of shares	88,937			$ 68	88,869
Issuance of shares from equity-based awards (in shares)				53,668
Issuance of shares from equity-based awards	(245)			$ 1	(246)
Retired shares (in shares)			(1,200,000)	(10,000)
Retired shares	(30,155)		$ (12)		(30,088)		(55)
Preferred dividends declared	(175)						(175)
Employee receivables from sale of stock	117				5		112
Stock-based compensation	3,569				3,569
Employee stock purchase plan additions	36				36
Ending balance (in shares) at Sep. 30, 2019			0	51,969,203
Ending balance at Sep. 30, 2019	602,435		$ 0	$ 520	518,816		65,198		17,901
Beginning balance (in shares) at Jun. 30, 2019			0	45,367,641
Beginning balance at Jun. 30, 2019	499,195		$ 0	$ 453	430,347		54,816		13,579
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	10,384						10,384
Change in unrealized appreciation on available-for-sale securities	4,322								4,322
Issuance of shares (in shares)				6,600,245
Issuance of shares	87,220			$ 67	87,154		(1)
Issuance of shares from equity-based awards (in shares)				1,317
Issuance of shares from equity-based awards	(10)				(10)
Employee receivables from sale of stock	0				1		(1)
Stock-based compensation	1,324				1,324
Ending balance (in shares) at Sep. 30, 2019			0	51,969,203
Ending balance at Sep. 30, 2019	602,435		$ 0	$ 520	518,816		65,198		17,901
Beginning balance (in shares) at Dec. 31, 2019			0	51,969,203
Beginning balance at Dec. 31, 2019	601,644		$ 0	$ 520	519,870		64,803		16,451
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	4,507						4,507
Change in unrealized appreciation on available-for-sale securities	9,330								9,330
Issuance of shares from equity-based awards (in shares)				226,575
Issuance of shares from equity-based awards	(868)			$ 1	(869)
Employee receivables from sale of stock	47				2		45
Stock-based compensation	3,202				3,202
Employee stock purchase plan additions	21				21
Ending balance (in shares) at Sep. 30, 2020			0	52,195,778
Ending balance at Sep. 30, 2020	617,883		$ 0	$ 521	522,226		69,355		25,781
Beginning balance (in shares) at Jun. 30, 2020			0	52,167,573
Beginning balance at Jun. 30, 2020	608,092		$ 0	$ 521	521,133		61,344		25,094
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	8,006						8,006
Change in unrealized appreciation on available-for-sale securities	687								687
Issuance of shares from equity-based awards (in shares)				28,205
Issuance of shares from equity-based awards	(115)				(115)
Employee receivables from sale of stock	6				1		5
Stock-based compensation	1,186				1,186
Employee stock purchase plan additions	21				21
Ending balance (in shares) at Sep. 30, 2020			0	52,195,778
Ending balance at Sep. 30, 2020	$ 617,883		$ 0	$ 521	$ 522,226		$ 69,355		$ 25,781