Debt - Schedule of Activity and Balances Associated with the Notes and Related Deferred Transaction Costs (Details) - USD ($) $ in Thousands			1 Months Ended		12 Months Ended
	Feb. 28, 2017	Mar. 18, 2016	Mar. 31, 2017	Nov. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Convertible Notes And Deferred Transaction Costs[Roll forward]
Less: amortization of deferred financing cost					$ (1,342)	$ (6,921)	$ (4,566)
Conversions					(4,912)	(137,941)	(40,989)
Convertible Senior Notes Due 2019
Convertible Notes And Deferred Transaction Costs[Roll forward]
Notes Balance, beginning of period					23,514	159,011
Deferred Debt Costs, beginning of period					849	7,770
Notes, net of Deferred Debt Costs, beginning of period					22,665	151,241
Less: amortization of deferred financing cost		$ (3,600)		$ (2,000)	(1,139)	(6,921)
Conversions		$ (79,800)	$ (4,900)	$ (55,700)	(4,911)	(135,497)
Notes Balance, end of period					18,603	23,514	159,011
Deferred Debt Costs, end of period					1,301	849	7,770
Less: amortization of debt modification cost	$ (1,591)
Notes, net of Deferred Debt Costs, end of period					$ 17,302	$ 22,665	$ 151,241