Convertible 4.5% Senior Notes (Details)	1 Months Ended	3 Months Ended		9 Months Ended
	Jun. 30, 2016 USD ($) item $ / shares	Sep. 30, 2017 USD ($) shares	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Convertible debt
Interest rate (as a percent)		4.50%	4.50%	4.50%	4.50%
Proceeds from issuance of debt					$ 96,608,000
Issuance of debt transaction costs					3,392,000
Fees for debt conversion				$ 1,683,000
Interest expense		$ 762,000	$ 1,150,000	3,012,000	1,288,000
Non-current deferred financing cost		$ 2,559,000		$ 2,559,000		$ 3,144,000
Convertible Notes
Convertible debt
Interest rate (as a percent)	4.50%	4.50%		4.50%
Principal amount of debt	$ 100,000,000	$ 3,100,000		$ 3,100,000
Proceeds from issuance of debt	96,600,000
Issuance of debt transaction costs	3,400,000
Debt converted		$ 96,900,000
Shares issued with debt conversion (in shares) | shares		25,882,421
Shares issued with debt conversion adjustment (in shares) | shares		2,744,881
Debt conversion loss		$ 22,200,000
Accrued interest forfeited		727,000
Charges to paid in capital		2,500,000
Transaction costs		1,700,000
Interest expense				3,000,000	$ 1,300,000
Principal amount of debt for conversion calculations	$ 1,000	1,000		1,000
Ratio issued upon conversion	238.7775
Initial conversion price (in dollars per share) | $ / shares	$ 4.19
Principal amount of notes to be repurchased under certain conditions (as a percent)	100.00%
Principal amount of notes to be repurchased upon default (as a percent)	100.00%
Additional interest for reporting requirement failure (as a percent)	0.50%
Default cure period	90 days
Additional interest for restricted event (as a percent)	0.50%
Number of additional interest rate percentage penalty circumstances | item	2
Maximum additional interest rate (as a percent)	0.50%
Non-current deferred financing cost		$ 78,000		$ 78,000