Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]	Noncontrolling Interest [Member]
Balance, value at Dec. 31, 2016	$ 421,646	$ 21	$ 81,715	$ 338,386	$ 1,524	$ 0
Balance, shares at Dec. 31, 2016		20,456,225
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	61,100			59,204		1,896
Distribution to noncontrolling interest	(1,896)					(1,896)
Unrealized income on investment, net of tax effect	679				679
Adjustment to pension benefit plans, net of taxes	0
Share-based compensation	2,504		2,643	(139)
Issuance of restricted and deferred stock units, value	(707)		(707)
Issuance of restricted and deferred stock units, shares		36,888
Employee stock purchase plan, value	$ 1,215		1,215
Employee stock purchase plan, shares	27,743	27,743
Dividends	$ (21,332)			(21,332)
Balance, value at Dec. 31, 2017	463,209	$ 21	84,866	376,119	2,203	0
Balance, shares at Dec. 31, 2017		20,520,856
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	38,767			38,767
Adjustment to pension benefit plans, net of taxes	0
Share-based compensation	2,020		2,117	(97)
Issuance of restricted and deferred stock units, value	(4,057)		(4,057)
Issuance of restricted and deferred stock units, shares		95,053
Employee stock purchase plan, value	$ 1,371		1,371
Employee stock purchase plan, shares	25,907	25,907
Common stock issued, shares		7,762,500
Common stock issued, value		$ 7
Dividends	$ (23,074)			(23,074)
Balance, value at Dec. 31, 2018	$ 889,312	$ 28	495,366	393,918	0	0
Balance, shares at Dec. 31, 2018	28,404,316	28,404,316
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 23,627			23,403		224
Distribution to noncontrolling interest	(224)					(224)
Unrealized income on investment, net of tax effect	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, value	(110)		(110)
Issuance of restricted and deferred stock units, shares		21,909
Employee stock purchase plan, value	$ 1,603		1,603
Employee stock purchase plan, shares	30,255	30,283
Common stock issued, value	$ 411,076		411,069
Common stock issuance cost	(10)		(10)
Dividends	(34,134)			(34,134)
Balance, value at Dec. 31, 2019	$ 889,984	$ 28	$ 506,639	$ 383,191	$ 126	$ 0
Balance, shares at Dec. 31, 2019	28,456,508	28,456,508