Capital Stock - Stockholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			$ 24,547	$ 19,099
Exercise of stock options (shares)			302,703.000	55,780.00
Exercise of stock options			$ 1,858	$ 142
Employee stock-based compensation			4,413	3,379
Non-employee stock-based compensation			24
Net shares settlements for taxes			(3,140)	(1,636)
Issuance of common stock, net of issuance costs			37,317	23,291
Issuance costs			179
Total comprehensive loss	$ (3,735)	$ (6,086)	(8,429)	(13,638)
Net loss	(3,735)	(6,280)	(8,429)	(13,740)
Ending balance	$ 52,530	$ 30,637	$ 52,530	$ 30,637
Accounting Standards Update 2014-09 [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Effect of new accounting principle					$ (4,060)
Accounting Standards Update 2016-01 [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Effect of new accounting principle					0
Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (shares)			48,365,000	41,255,000
Beginning balance			$ 5	$ 4
Exercise of stock options (shares)			303,000	56,000
Release of stock awards (shares)			824,000	1,079,000
Net shares settlements for taxes (shares)			(297,000)	(391,000)
Issuance of common stock, net of issuance costs (shares)			4,313,000	6,325,000
Issuance of common stock, net of issuance costs				$ 1
Ending balance (shares)	53,508,000	48,324,000	53,508,000	48,324,000
Ending balance	$ 5	$ 5	$ 5	$ 5
Additional Paid-in Capital [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			340,079	311,164
Exercise of stock options			1,858	142
Employee stock-based compensation			4,413	3,379
Non-employee stock-based compensation			24
Net shares settlements for taxes			(3,140)	(1,636)
Issuance of common stock, net of issuance costs			37,317	23,290
Ending balance	380,551	336,339	380,551	336,339
AOCI Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			(472)	0
Total comprehensive loss				102
Ending balance	0	102	0	102
AOCI Attributable to Parent [Member] | Accounting Standards Update 2016-01 [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Effect of new accounting principle					472
Accumulated Deficit [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			(315,065)	(292,069)
Total comprehensive loss				(13,740)
Net loss			(8,429)
Ending balance	$ (328,026)	$ (305,809)	$ (328,026)	$ (305,809)
Accumulated Deficit [Member] | Accounting Standards Update 2014-09 [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Effect of new accounting principle					(4,060)
Accumulated Deficit [Member] | Accounting Standards Update 2016-01 [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Effect of new accounting principle					$ (472)