Capital Stock - Stockholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			$ 24,547	$ 19,099
Exercise of stock options (shares)			729,596	63,509
Exercise of stock options			$ 4,319	$ 175
Employee stock-based compensation			6,183	5,212
Non-employee stock-based compensation			24
Net shares settlements for taxes			(3,140)	(1,670)
Issuance of common stock, net of issuance costs			37,317	23,230
Issuance costs			180	553
Total comprehensive loss	$ (1,988)	$ (10,316)	(10,417)	(23,953)
Net loss	(1,988)	(10,226)	(10,417)	(23,966)
Ending balance	$ 54,773	$ 22,093	$ 54,773	$ 22,093
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)			730,000	64,000
Release of stock awards (shares)			824,000	1,096,000
Net shares settlements for taxes (shares)			(297,000)	(397,000)
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)	53,935,000	48,343,000	53,935,000	48,343,000
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			4,319	175
Employee stock-based compensation			6,183	5,212
Non-employee stock-based compensation			24
Net shares settlements for taxes			(3,140)	(1,670)
Issuance of common stock, net of issuance costs			37,317	23,229
Ending balance	384,782	338,110	384,782	338,110
AOCI Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			(472)	0
Total comprehensive loss				13
Ending balance	0	13	0	13
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				(23,966)
Net loss			(10,417)
Ending balance	$ (330,014)	$ (316,035)	$ (330,014)	$ (316,035)
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)