Consolidated Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Accumulated Other Comprehensive Income (Loss) Net of Tax	Retained Earnings
Beginning balance (in shares) at Dec. 31, 2014		21,365
Beginning balance at Dec. 31, 2014	$ 264,951	$ 162,575	$ 2,814	$ 99,562
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	39,135			39,135
Other comprehensive loss, net of tax	(1,270)		(1,270)
Comprehensive income	37,865
Common stock issued under various employee plans, net (in shares)		289
Common stock issued under various employee plans, net	6,342	$ 6,342
Stock issuance pursuant to exercise of Warrant (in shares)		1,487
Stock issuance pursuant to exercise of Warrant	931	$ 931
Cash dividends paid	(8,630)			(8,630)
Ending balance (in shares) at Dec. 31, 2015		23,141
Ending balance at Dec. 31, 2015	301,459	$ 169,848	1,544	130,067
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	38,766			38,766
Other comprehensive loss, net of tax	(852)		(852)
Comprehensive income	37,914
Common stock issued for AEB acquisition (in shares)		1,470
Common stock issued for AEB acquisition	22,727	$ 22,727
Common stock issued under various employee plans, net (in shares)		707
Common stock issued under various employee plans, net	10,049	$ 10,049
Stock issuance pursuant to exercise of Warrant (in shares)		1,000
Stock issuance pursuant to exercise of Warrant	2,685	$ 2,685
Cash dividends paid	(12,187)			(12,187)
Ending balance (in shares) at Dec. 31, 2016		26,318
Ending balance at Dec. 31, 2016	362,647	$ 205,309	692	156,646
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	39,796			39,796
Other comprehensive loss, net of tax	(309)		(309)
Comprehensive income	39,487
Common stock issued under various employee plans, net (in shares)		701
Common stock issued under various employee plans, net	12,246	$ 12,246
Cash dividends paid	(12,748)			(12,748)
Ending balance (in shares) at Dec. 31, 2017		27,019
Ending balance at Dec. 31, 2017	$ 401,632	$ 217,555	$ 383	$ 183,694