Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Additional Paid-in Capital	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Income	Accumulated Other Comprehensive Income Cumulative Effect, Period of Adoption, Adjustment	Noncontrolling Interest
Beginning balance (in shares) at Dec. 31, 2017			20,520,856
Beginning balance at Dec. 31, 2017	$ 463,209	$ 0	$ 21	$ 84,866	$ 376,119	$ 2,203	$ 2,203	$ (2,203)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	38,767				38,767
Unrealized income (loss) on investment, net of taxes	0
Adjustment to pension benefit plans, net of taxes	0
Share-based compensation	2,020			2,117	(97)
Issuance of restricted and deferred stock units (in shares)			95,053
Issuance of restricted and deferred stock units	$ (4,057)			(4,057)
Employee stock purchase plan (in shares)	25,907		25,907
Employee stock purchase plan	$ 1,371			1,371
Common stock issued (in shares)			7,762,500
Common stock issued	411,076		$ 7	411,069
Dividends paid	(23,074)				(23,074)
Ending balance (in shares) at Dec. 31, 2018			28,404,316
Ending balance at Dec. 31, 2018	889,312	$ 97	$ 28	495,366	393,918	$ 97	0		0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	23,627				23,403				224
Distribution to noncontrolling interest	(224)								(224)
Unrealized income (loss) on investment, net of taxes	117						117
Adjustment to pension benefit plans, net of taxes	9						9
Share-based compensation	3,313			3,406	(93)
Share-based compensation related to business combination	6,384			6,384
Issuance of restricted and deferred stock units (in shares)			21,909
Issuance of restricted and deferred stock units	$ (110)			(110)
Employee stock purchase plan (in shares)	30,255		30,283
Employee stock purchase plan	$ 1,603			1,603
Common stock issuance cost	(10)			(10)
Dividends paid	$ (34,134)				(34,134)
Ending balance (in shares) at Dec. 31, 2019	28,456,508		28,456,508
Ending balance at Dec. 31, 2019	$ 889,984		$ 28	506,639	383,191		126		0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	61,515				61,515
Unrealized income (loss) on investment, net of taxes	(310)						(310)
Adjustment to pension benefit plans, net of taxes	(880)						(880)
Share-based compensation	3,393			3,553	(160)
Issuance of restricted and deferred stock units (in shares)			68,347
Issuance of restricted and deferred stock units	$ (1,863)		$ 1	(1,864)
Employee stock purchase plan (in shares)	31,750		31,750
Employee stock purchase plan	$ 1,830			1,830
Dividends paid	$ (36,509)				(36,509)
Ending balance (in shares) at Dec. 31, 2020	28,556,605		28,556,605
Ending balance at Dec. 31, 2020	$ 917,160		$ 29	$ 510,158	$ 408,037		$ (1,064)		$ 0