Capital Stock - Stockholders' Equity (Details) - USD ($) $ in Thousands	1 Months Ended	6 Months Ended
	Apr. 30, 2017	Jun. 30, 2017	Jun. 30, 2016
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' equity beginning balance		$ 19,099	$ 22,879
Exercise of stock options (shares)		55,780	323,981
Exercise of stock options		$ 142	$ 837
Release of stock awards		(1,636)	(708)
Employee stock-based compensation		3,379	2,631
Issuance of common stock, net of issuance costs (shares)	6,300,000
Issuance of common stock, net of issuance costs		23,291
Cancelled shares			(790)
Total comprehensive loss		(13,638)	(5,169)
Stockholders' equity ending balance		$ 30,637	$ 19,680
Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (shares)		41,255,000	40,343,000
Stockholders' equity beginning balance		$ 4	$ 4
Exercise of stock options (shares)		56,000	324,000
Release of stock awards (shares)		688,000	700,000
Issuance of common stock, net of issuance costs (shares)		6,325,000
Issuance of common stock, net of issuance costs		$ 1
Cancelled shares (shares)			(196,000)
Ending balance (shares)		48,324,000	41,171,000
Stockholders' equity ending balance		$ 5	$ 4
Additional Paid-in Capital [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' equity beginning balance		311,164	305,981
Exercise of stock options		142	837
Release of stock awards		(1,636)	(708)
Employee stock-based compensation		3,379	2,631
Issuance of common stock, net of issuance costs		23,290
Cancelled shares			(790)
Stockholders' equity ending balance		336,339	307,951
Accumulated Other Comprehensive Income (Loss) [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' equity beginning balance		0	405
Total comprehensive loss		102	(434)
Stockholders' equity ending balance		102	(29)
Accumulated Deficit [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stockholders' equity beginning balance		(292,069)	(283,511)
Total comprehensive loss		(13,740)	(4,735)
Stockholders' equity ending balance		$ (305,809)	$ (288,246)