Condenced Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common stock	Additional paid-in capital	Accumulated other comprehensive income (loss)	Accumulated deficit
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Impact of adoption of new accounting standard ASU 2016-16	$ (1,824)				$ (1,824)
Beginning balance (in shares) at Dec. 31, 2017		44,219
Beginning balance at Dec. 31, 2017	194,451	$ 111	$ 545,953	$ 398	(352,011)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	(44,875)			(7,967)	(36,908)
Issuance of common stock upon exercise of stock options (in shares)		591
Issuance of common stock upon exercise of stock options	2,563	$ 1	2,562
Issuance of common stock under employee stock purchase plan (in shares)		234
Issuance of common stock under employee stock purchase plan	1,243	$ 1	1,242
Issuance of common stock for vested restricted stock units (in shares)		916
Issuance of common stock for vested restricted stock units	0	$ 2	(2)
Tax withholding related to vesting of restricted stock units (in shares)		(120)
Tax withholding related to vesting of restricted stock units	(747)		(747)
Stock-based compensation costs	10,363		10,363
Ending Balance (in shares) at Sep. 30, 2018		45,840
Ending balance at Sep. 30, 2018	161,174	$ 115	559,371	(7,569)	(390,743)
Beginning balance (in shares) at Jun. 30, 2018		44,906
Beginning balance at Jun. 30, 2018	169,458	$ 112	553,945	(1,981)	(382,618)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	(13,713)			(5,588)	(8,125)
Issuance of common stock upon exercise of stock options (in shares)		403
Issuance of common stock upon exercise of stock options	1,861	$ 1	1,860
Issuance of common stock under employee stock purchase plan (in shares)		0
Issuance of common stock under employee stock purchase plan	0	$ 0	0
Issuance of common stock for vested restricted stock units (in shares)		604
Issuance of common stock for vested restricted stock units	0	$ 2	(2)
Tax withholding related to vesting of restricted stock units (in shares)		(73)
Tax withholding related to vesting of restricted stock units	(471)		(471)
Stock-based compensation costs	4,039		4,039
Ending Balance (in shares) at Sep. 30, 2018		45,840
Ending balance at Sep. 30, 2018	161,174	$ 115	559,371	(7,569)	(390,743)
Beginning balance (in shares) at Dec. 31, 2018		46,378
Beginning balance at Dec. 31, 2018	160,240	$ 116	564,722	(7,126)	(397,472)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	(22,613)			(3,468)	(19,145)
Offering costs	(46)		(46)
Issuance of common stock in exchange for research and development services (in shares)		276
Issuance of common stock in exchange for research and development services	1,500	$ 1	1,499
Issuance of common stock upon exercise of stock options (in shares)		265
Issuance of common stock upon exercise of stock options	969		969
Issuance of common stock under employee stock purchase plan (in shares)		254
Issuance of common stock under employee stock purchase plan	1,235	$ 1	1,234
Issuance of common stock for vested restricted stock units (in shares)		996
Issuance of common stock for vested restricted stock units	0	$ 2	(2)
Tax withholding related to vesting of restricted stock units (in shares)		(152)
Tax withholding related to vesting of restricted stock units	(705)		(705)
Stock-based compensation costs	9,417		9,417
Ending Balance (in shares) at Sep. 30, 2019		48,017
Ending balance at Sep. 30, 2019	149,997	$ 120	577,088	(10,594)	(416,617)
Beginning balance (in shares) at Jun. 30, 2019		47,152
Beginning balance at Jun. 30, 2019	147,984	$ 118	572,734	(5,979)	(418,889)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	(2,343)			(4,615)	2,272
Offering costs	(46)		(46)
Issuance of common stock in exchange for research and development services (in shares)		276
Issuance of common stock in exchange for research and development services	1,500	$ 1	1,499
Issuance of common stock upon exercise of stock options (in shares)		98
Issuance of common stock upon exercise of stock options	397		397
Issuance of common stock under employee stock purchase plan (in shares)		0
Issuance of common stock under employee stock purchase plan	0	$ 0	0
Issuance of common stock for vested restricted stock units (in shares)		573
Issuance of common stock for vested restricted stock units	0	$ 1	(1)
Tax withholding related to vesting of restricted stock units (in shares)		(82)
Tax withholding related to vesting of restricted stock units	(378)		(378)
Stock-based compensation costs	2,883		2,883
Ending Balance (in shares) at Sep. 30, 2019		48,017
Ending balance at Sep. 30, 2019	$ 149,997	$ 120	$ 577,088	$ (10,594)	$ (416,617)