Convertible Senior Notes (Details) $ / shares in Units, $ in Thousands					1 Months Ended	2 Months Ended		3 Months Ended					12 Months Ended
	Dec. 31, 2015 USD ($) shares	Nov. 01, 2015 USD ($)	May. 01, 2015 USD ($)	Nov. 03, 2014 USD ($)	Nov. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) shares	Dec. 31, 2014 USD ($) shares	Nov. 03, 2014 USD ($) $ / shares	Oct. 31, 2014 USD ($)
Interest on senior convertible notes
Interest payable at the beginning of period											$ 2,500		$ 2,500
Accrued interest expense														$ 2,500
Interest payment													(13,379)
Interest payable at the end of period	$ 1,988					$ 2,500	$ 2,500	$ 1,988				$ 2,500	1,988	2,500
Convertible Notes And Deferred Transaction Costs
Less: amortization												(411)	(4,566)	(411)
Conversions													(40,989)
Notes, net of Transaction Costs, end of period	206,700							206,700					206,700
Convertible Senior Notes Due 2019
Convertible Senior Notes
Aggregate principal amount (in dollars)	159,011			$ 200,000	$ 200,000	200,000	200,000	159,011	$ 177,787	$ 200,000	200,000	200,000	200,000	200,000	$ 200,000	$ 200,000
Interest rate (as a percent)															7.50%
Additional aggregate principal amount pertaining to the over-allotment option granted (in dollars)															$ 25,000
Net proceeds from offering (in dollars)				$ 187,300
Interest on senior convertible notes
Interest payable at the beginning of period								4,969	2,222	6,250	2,500		2,500
Accrued interest expense							2,500	2,982	2,747	3,388	3,750
Interest payment		$ (5,963)	$ (7,416)
Interest payable at the end of period	$ 1,988					2,500	2,500	1,988	4,969	2,222	6,250	2,500	$ 1,988	$ 2,500
Conversion rate (as a percent)				0.3215434
Conversion price (in dollars per share) | $ / shares															$ 3.11
Number of shares issued on conversion of debt | shares	51,128,938												13,200,000	64,308,680
Convertible Notes And Deferred Transaction Costs
Notes Balance, beginning of period					200,000	200,000		159,011	177,787	200,000	200,000		$ 200,000
Transactions Costs, beginning of period																12,747
Notes, net of Transaction Costs, beginning of period					187,253	187,253		150,735	167,967	188,281	187,664		187,664
Less: amortization					$ 411	(411)		506	1,544	1,899	617		4,600
Conversions									(18,776)	(22,213)			(41,000)
Notes Balance, end of period	$ 159,011			$ 200,000		200,000	200,000	159,011	159,011	177,787	200,000	200,000	159,011	$ 200,000
Transactions Costs, end of period	7,770					12,336	12,336	7,770	8,276	9,820	11,719	12,336	7,770	12,336
Notes, net of Transaction Costs, end of period	$ 151,241					$ 187,664	$ 187,664	$ 151,241	$ 150,735	$ 167,967	$ 188,281	$ 187,664	$ 151,241	$ 187,664
Deferred financing costs at issuance																$ 12,747