Condensed Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ 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
Beginning balance at Dec. 31, 2017	$ 554,341	$ 48	$ (185,074)	$ 585,755	$ 159,725	$ (6,113)
Treasury Stock, Beginning of period (in shares) at Dec. 31, 2017			(9,145)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	2,720				2,720
Other comprehensive income (loss)	2,674					2,674
Share-based compensation	6,528			6,528
Issuance of common stock under employee stock plans (in shares)		428
Issuance of common stock under employee stock plans	9,541	$ 0		9,541
Common Stock, End of period (in shares) at Mar. 31, 2018		48,005
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Tax payments related to restricted stock units	(1,300)			(1,300)
Treasury Stock, End of period (in shares) at Mar. 31, 2018			(9,145)
Ending balance at Mar. 31, 2018	574,504	$ 48	$ (185,074)	600,524	162,445	(3,439)
Common Stock, Beginning of period (in shares) at Dec. 31, 2017		47,577
Beginning balance at Dec. 31, 2017	554,341	$ 48	$ (185,074)	585,755	159,725	(6,113)
Treasury Stock, Beginning of period (in shares) at Dec. 31, 2017			(9,145)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	22,936
Other comprehensive income (loss)	(2,971)
Common Stock, End of period (in shares) at Sep. 30, 2018		48,760
Treasury Stock, End of period (in shares) at Sep. 30, 2018			(9,145)
Ending balance at Sep. 30, 2018	619,238	$ 49	$ (185,074)	630,686	182,661	(9,084)
Common Stock, Beginning of period (in shares) at Mar. 31, 2018		48,005
Beginning balance at Mar. 31, 2018	574,504	$ 48	$ (185,074)	600,524	162,445	(3,439)
Treasury Stock, Beginning of period (in shares) at Mar. 31, 2018			(9,145)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	6,588				6,588
Other comprehensive income (loss)	(4,504)					(4,504)
Share-based compensation	7,238			7,238
Issuance of common stock under employee stock plans (in shares)		341
Issuance of common stock under employee stock plans	6,576	$ 0		6,576
Common Stock, End of period (in shares) at Jun. 30, 2018		48,346
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Tax payments related to restricted stock units	(1,762)			(1,762)
Treasury Stock, End of period (in shares) at Jun. 30, 2018			(9,145)
Ending balance at Jun. 30, 2018	588,640	$ 48	$ (185,074)	612,576	169,033	(7,943)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	13,628				13,628
Other comprehensive income (loss)	(1,141)					(1,141)
Share-based compensation	7,085			7,085
Issuance of common stock under employee stock plans (in shares)		414
Issuance of common stock under employee stock plans	11,612	$ 1		11,611
Common Stock, End of period (in shares) at Sep. 30, 2018		48,760
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Tax payments related to restricted stock units	(586)			(586)
Treasury Stock, End of period (in shares) at Sep. 30, 2018			(9,145)
Ending balance at Sep. 30, 2018	619,238	$ 49	$ (185,074)	630,686	182,661	(9,084)
Common Stock, Beginning of period (in shares) at Dec. 31, 2018		49,480
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)		(9,145)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 3,284				3,284
Other comprehensive income (loss)	352					352
At the market equity offering, net of costs ( in shares )		243
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
Issuance of common stock under employee stock plans	20,526	$ 0		20,526
Common Stock, End of period (in shares) at Mar. 31, 2019		50,351
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Tax payments related to restricted stock units	(1,920)			(1,920)
Treasury Stock, End of period (in shares) at Mar. 31, 2019			(9,145)
Ending balance at Mar. 31, 2019	730,485	$ 50	$ (185,074)	725,273	200,738	(10,502)
Common Stock, Beginning of period (in shares) at Dec. 31, 2018		49,480
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)		(9,145)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 39,243
Other comprehensive income (loss)	$ (3,547)
Common Stock, End of period (in shares) at Sep. 30, 2019		51,050
Treasury Stock, End of period (in shares) at Sep. 30, 2019	(9,145)		(9,145)
Ending balance at Sep. 30, 2019	$ 807,533	$ 51	$ (185,074)	770,260	236,697	(14,401)
Common Stock, Beginning of period (in shares) at Mar. 31, 2019		50,351
Beginning balance at Mar. 31, 2019	730,485	$ 50	$ (185,074)	725,273	200,738	(10,502)
Treasury Stock, Beginning of period (in shares) at Mar. 31, 2019			(9,145)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	15,976				15,976
Other comprehensive income (loss)	(1,074)					(1,074)
At the market equity offering, net of costs ( in shares )		217
At the market equity offering, net of costs	17,590			17,590
Share-based compensation	8,260			8,260
Issuance of common stock under employee stock plans (in shares)		216
Issuance of common stock under employee stock plans	4,807	$ 1		4,806
Common Stock, End of period (in shares) at Jun. 30, 2019		50,784
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Tax payments related to restricted stock units	(2,802)			(2,802)
Treasury Stock, End of period (in shares) at Jun. 30, 2019			(9,145)
Ending balance at Jun. 30, 2019	773,242	$ 51	$ (185,074)	753,127	216,714	(11,576)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	19,983				19,983
Other comprehensive income (loss)	(2,825)					(2,825)
Share-based compensation	8,505			8,505
Issuance of common stock under employee stock plans (in shares)		266
Issuance of common stock under employee stock plans	9,696	$ 0		9,696
Common Stock, End of period (in shares) at Sep. 30, 2019		51,050
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Tax payments related to restricted stock units	$ (1,068)			(1,068)
Treasury Stock, End of period (in shares) at Sep. 30, 2019	(9,145)		(9,145)
Ending balance at Sep. 30, 2019	$ 807,533	$ 51	$ (185,074)	$ 770,260	$ 236,697	$ (14,401)