Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-In Capital	Accumulated Earnings	Accumulated Other Comprehensive Income (Loss)
Common Stock, Beginning of period (in shares) at Dec. 31, 2017		47,577,000
Beginning balance at Dec. 31, 2017	$ 554,339	$ 48	$ (185,074)	$ 585,756	$ 159,722	$ (6,113)
Treasury Stock, Beginning of period (in shares) at Dec. 31, 2017			(9,145,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	2,720				2,720
Other comprehensive income	2,674					2,674
Share-based compensation	6,528			6,528
Issuance of common stock under employee stock plans (in shares)		428,000
Issuance of common stock under employee stock plans	9,541	$ 0		9,541
Tax payments related to restricted stock units	(1,300)			(1,300)
Common Stock, End of period (in shares) at Mar. 31, 2018		48,005,000
Ending balance at Mar. 31, 2018	574,502	$ 48	$ (185,074)	600,525	162,442	(3,439)
Treasury Stock, End of period (in shares) at Mar. 31, 2018			(9,145,000)
Common Stock, Beginning of period (in shares) at Dec. 31, 2018		49,480,000
Beginning balance at Dec. 31, 2018	$ 679,617	$ 50	$ (185,074)	678,041	197,454	(10,854)
Treasury Stock, Beginning of period (in shares) at Dec. 31, 2018	(9,145,000)		(9,145,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 3,284				3,284
Other comprehensive income	352					352
At the market equity offering, net of costs ( in shares )		243,000
At the market equity offering, net of costs	20,216			20,216
Share-based compensation	8,410			8,410
Issuance of common stock under employee stock plans (in shares)		628,000
Issuance of common stock under employee stock plans	20,526	$ 0		20,526
Tax payments related to restricted stock units	(1,920)			(1,920)
Common Stock, End of period (in shares) at Mar. 31, 2019		50,351,000
Ending balance at Mar. 31, 2019	$ 730,485	$ 50	$ (185,074)	$ 725,273	$ 200,738	$ (10,502)
Treasury Stock, End of period (in shares) at Mar. 31, 2019	(9,145,000)		(9,145,000)