CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Common Stock	Retained Earnings	Accumulated Other Comprehensive Loss	Total
Beginning balance at Dec. 31, 2016	$ 206,186	$ 293,885	$ (1,882)	$ 498,189
Beginning balance (in shares) at Dec. 31, 2016	44,645
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		27,523		27,523
Other comprehensive income (loss)			3,416	3,416
Stock-based compensation expense	$ 4,075			4,075
Options exercised	$ 5,689			5,689
Options exercised (in shares)	404
Issuance of common stock under Employee Stock Purchase Plan	$ 836			836
Issuance of common stock under Employee Stock Purchase Plans (in shares)	24
Issuance of common stock, net of offering costs	$ 136,606			$ 136,606
Issuance of common stock, net of offering costs (in shares)	5,175
Shares surrendered in exchange for exercise of stock options (in shares)				0
Ending balance at Dec. 31, 2017	$ 353,392	321,408	1,534	$ 676,334
Ending balance (in shares) at Dec. 31, 2017	50,248
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		42,017		42,017
Other comprehensive income (loss)			(3,567)	(3,567)
Stock-based compensation expense	$ 6,117			6,117
Options exercised	$ 10,634			10,634
Options exercised (in shares)	690
Issuance of common stock under Employee Stock Purchase Plan	$ 1,087			1,087
Issuance of common stock under Employee Stock Purchase Plans (in shares)	22
Issuance of common stock, net of offering costs	$ 205,030			205,030
Issuance of common stock, net of offering costs (in shares)	4,025
Shares surrendered in exchange for payment of payroll tax liabilities	$ (2,616)			(2,616)
Shares surrendered in exchange for payment of payroll tax liabilities (in shares)	(49)
Shares surrendered in exchange for exercise of stock options	$ (2,261)			$ (2,261)
Shares surrendered in exchange for exercise of stock options (in shares)	(43)			(43)
Ending balance at Dec. 31, 2018	$ 571,383	363,425	(2,033)	$ 932,775
Ending balance (in shares) at Dec. 31, 2018	54,893			54,893
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		5,451		$ 5,451
Reclassification adjustment upon adoption of ASU | ASU 2016-02		93		93
Reclassification adjustment upon adoption of ASU | ASU 2018-02		(748)	748
Other comprehensive income (loss)			(4,009)	(4,009)
Stock-based compensation expense	$ 9,382			9,382
Options exercised	$ 4,930			$ 4,930
Options exercised (in shares)	288			288
Issuance of common stock under Employee Stock Purchase Plan	$ 1,415			$ 1,415
Issuance of common stock under Employee Stock Purchase Plans (in shares)	35
Shares surrendered in exchange for exercise of stock options	$ (93)			$ (93)
Shares surrendered in exchange for exercise of stock options (in shares)	(3)			(3)
Ending balance at Dec. 31, 2019	$ 587,017	$ 368,221	$ (5,294)	$ 949,944
Ending balance (in shares) at Dec. 31, 2019	55,213			55,213