Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Non- controlling Interest
Beginning Balance at Dec. 31, 2017	$ 364,879	$ 98	$ 263,835	$ 102,391	$ (2,146)	$ 701
Comprehensive income:
Net income	30,403			30,173		230
Other comprehensive income (loss)	(4,974)				(4,974)
Stock-based compensation expense	3,613		3,613
Exercise of stock options, net	1,224	1	1,223
Issuance of common stock	167		167
Purchase and retirement of common stock	(17,210)	(3)	(17,207)
Distribution to noncontrolling interest	(199)					(199)
Ending Balance at Sep. 30, 2018	377,903	96	251,631	133,501	(8,057)	732
Beginning Balance at Jun. 30, 2018	371,285	96	254,564	122,642	(6,718)	701
Comprehensive income:
Net income	10,939			10,859		80
Other comprehensive income (loss)	(1,339)				(1,339)
Stock-based compensation expense	1,299		1,299
Exercise of stock options, net	262	1	261
Issuance of common stock	59		59
Purchase and retirement of common stock	(4,553)	(1)	(4,552)
Distribution to noncontrolling interest	(49)					(49)
Ending Balance at Sep. 30, 2018	377,903	96	251,631	133,501	(8,057)	732
Comprehensive income:
Cumulative Effect of New Accounting Principle in Period of Adoption				937
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2016-01					(937)
Beginning Balance at Dec. 31, 2018	387,352	95	247,790	144,364	(5,640)	743
Comprehensive income:
Net income	42,606			42,346		260
Other comprehensive income (loss)	10,316				10,316
Stock-based compensation expense	3,643		3,643
Exercise of stock options, net	4,382	2	4,380
Issuance of common stock	449		449
Purchase and retirement of common stock	(19,731)	(3)	(19,728)
Distribution to noncontrolling interest	(275)					(275)
Ending Balance at Sep. 30, 2019	428,742	94	236,534	186,710	4,676	728
Beginning Balance at Jun. 30, 2019	412,148	94	234,963	173,180	3,178	733
Comprehensive income:
Net income	13,612			13,530		82
Other comprehensive income (loss)	1,498				1,498
Stock-based compensation expense	1,144		1,144
Exercise of stock options, net	1,200		1,200
Issuance of common stock	166		166
Purchase and retirement of common stock	(939)	0	(939)
Distribution to noncontrolling interest	(87)					(87)
Ending Balance at Sep. 30, 2019	$ 428,742	$ 94	$ 236,534	$ 186,710	$ 4,676	$ 728