Financial Instruments - Convertible Notes (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Aug. 31, 2016	Jun. 30, 2016	Jan. 31, 2016	Apr. 17, 2014	Feb. 28, 2013	Aug. 01, 2011
3.75% Convertible Notes
Fair value measurement
Interest rate (as a percent)	3.75%	3.75%	3.75%	3.75%			3.75%
3.50% Convertible Notes
Fair value measurement
Interest rate (as a percent)	3.50%		3.50%			3.50%
3.50% Series A Convertible Notes
Fair value measurement
Interest rate (as a percent)	3.50%		3.50%		3.50%
Non-recurring basis | Carrying Value
Fair value measurement
Long term debt	$ 170,168		$ 210,412
Non-recurring basis | Carrying Value | 3.75% Convertible Notes
Fair value measurement
Long term debt			36,400
Non-recurring basis | Carrying Value | 3.50% Convertible Notes
Fair value measurement
Long term debt	43,642		43,195
Non-recurring basis | Carrying Value | 3.50% Series A Convertible Notes
Fair value measurement
Long term debt	67,748		66,613
Non-recurring basis | Carrying Value | Secured Loan
Fair value measurement
Long term debt	58,778		64,204
Non-recurring basis | Fair Value
Fair value measurement
Long term debt	181,035		233,194
Non-recurring basis | Fair Value | 3.75% Convertible Notes
Fair value measurement
Long term debt			36,487
Non-recurring basis | Fair Value | 3.50% Convertible Notes
Fair value measurement
Long term debt	47,472		51,450
Non-recurring basis | Fair Value | 3.50% Series A Convertible Notes
Fair value measurement
Long term debt	74,785		81,053
Non-recurring basis | Fair Value | Secured Loan
Fair value measurement
Long term debt	$ 58,778		$ 64,204