CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Common Stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Total
Beginning balance at Dec. 31, 2017	$ 353,392	$ 321,408	$ 1,534	$ 676,334
Beginning balance (in shares) at Dec. 31, 2017	50,248
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)		5,269		5,269
Other comprehensive income/loss			4,072	4,072
Stock-based compensation expense	$ 1,256			1,256
Options exercised	$ 1,286			1,286
Options exercised (in shares)	91
Issuance of common stock under Employee Stock Purchase Plan	$ 294			294
Issuance of common stock under Employee Stock Purchase Plans (in shares)	7
Ending balance at Mar. 31, 2018	$ 356,228	326,677	5,606	688,511
Ending balance (in shares) at Mar. 31, 2018	50,346
Beginning balance at Dec. 31, 2017	$ 353,392	321,408	1,534	676,334
Beginning balance (in shares) at Dec. 31, 2017	50,248
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)				32,828
Other comprehensive income/loss				(610)
Shares surrendered in exchange for exercise of stock options				$ (2,262)
Shares surrendered in exchange for exercise of stock options (in shares)				(43)
Ending balance at Sep. 30, 2018	$ 568,051	354,236	924	$ 923,211
Ending balance (in shares) at Sep. 30, 2018	54,802
Beginning balance at Mar. 31, 2018	$ 356,228	326,677	5,606	688,511
Beginning balance (in shares) at Mar. 31, 2018	50,346
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)		10,941		10,941
Other comprehensive income/loss			(3,540)	(3,540)
Stock-based compensation expense	$ 1,565			1,565
Options exercised	$ 5,307			5,307
Options exercised (in shares)	357
Issuance of common stock under Employee Stock Purchase Plan	$ 220			220
Issuance of common stock under Employee Stock Purchase Plans (in shares)	4
Shares surrendered in exchange for payment of payroll tax liabilities	$ (2,065)			(2,065)
Shares surrendered in exchange for payment of payroll tax liabilities (in shares)	(40)
Shares surrendered in exchange for exercise of stock options	$ (1,685)			(1,685)
Shares surrendered in exchange for exercise of stock options (in shares)	(32)
Ending balance at Jun. 30, 2018	$ 359,570	337,618	2,066	699,254
Ending balance (in shares) at Jun. 30, 2018	50,635
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)		16,619		16,619
Other comprehensive income/loss			(1,142)	(1,142)
Stock-based compensation expense	$ 1,673			1,673
Options exercised	$ 2,624			2,624
Options exercised (in shares)	158
Issuance of common stock under Employee Stock Purchase Plan	$ 282			282
Issuance of common stock under Employee Stock Purchase Plans (in shares)	5
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	$ (551)			(551)
Shares surrendered in exchange for payment of payroll tax liabilities (in shares)	(10)
Shares surrendered in exchange for exercise of stock options	$ (577)			(577)
Shares surrendered in exchange for exercise of stock options (in shares)	(11)
Ending balance at Sep. 30, 2018	$ 568,051	354,236	924	923,211
Ending balance (in shares) at Sep. 30, 2018	54,802
Beginning balance at Dec. 31, 2018	$ 571,383	363,425	(2,033)	$ 932,775
Beginning balance (in shares) at Dec. 31, 2018	54,893			54,893
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)		6,195		$ 6,195
Reclassify deferred gain on sale-leaseback upon adoption of ASC 842		93		93
Other comprehensive income/loss			(2,515)	(2,515)
Stock-based compensation expense	$ 1,766			1,766
Options exercised	$ 1,365			1,365
Options exercised (in shares)	95
Issuance of common stock under Employee Stock Purchase Plan	$ 432			432
Issuance of common stock under Employee Stock Purchase Plans (in shares)	7
Ending balance at Mar. 31, 2019	$ 574,946	369,713	(4,548)	940,111
Ending balance (in shares) at Mar. 31, 2019	54,995
Beginning balance at Dec. 31, 2018	$ 571,383	363,425	(2,033)	$ 932,775
Beginning balance (in shares) at Dec. 31, 2018	54,893			54,893
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)				$ 9,656
Other comprehensive income/loss				(6,061)
Shares surrendered in exchange for exercise of stock options				$ (93)
Shares surrendered in exchange for exercise of stock options (in shares)				(3)
Ending balance at Sep. 30, 2019	$ 584,161	373,174	(8,094)	$ 949,241
Ending balance (in shares) at Sep. 30, 2019	55,208			55,208
Beginning balance at Mar. 31, 2019	$ 574,946	369,713	(4,548)	$ 940,111
Beginning balance (in shares) at Mar. 31, 2019	54,995
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)		6,859		6,859
Other comprehensive income/loss			(599)	(599)
Stock-based compensation expense	$ 2,523			2,523
Options exercised	$ 1,441			1,441
Options exercised (in shares)	78
Issuance of common stock under Employee Stock Purchase Plan	$ 340			340
Issuance of common stock under Employee Stock Purchase Plans (in shares)	6
Ending balance at Jun. 30, 2019	$ 579,250	376,572	(5,147)	950,675
Ending balance (in shares) at Jun. 30, 2019	55,079
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)		(3,398)		(3,398)
Other comprehensive income/loss			(2,947)	(2,947)
Stock-based compensation expense	$ 2,626			2,626
Options exercised	$ 2,037			2,037
Options exercised (in shares)	120
Issuance of common stock under Employee Stock Purchase Plan	$ 341			341
Issuance of common stock under Employee Stock Purchase Plans (in shares)	12
Shares surrendered in exchange for exercise of stock options	$ (93)			(93)
Shares surrendered in exchange for exercise of stock options (in shares)	(3)
Ending balance at Sep. 30, 2019	$ 584,161	$ 373,174	$ (8,094)	$ 949,241
Ending balance (in shares) at Sep. 30, 2019	55,208			55,208