Senior Convertible Notes (Details) $ / shares in Units, $ in Thousands, shares in Millions			2 Months Ended	3 Months Ended				9 Months Ended
	May. 01, 2015 USD ($)	Nov. 03, 2014 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2015 USD ($) shares	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) shares	Sep. 30, 2014 USD ($)	Nov. 03, 2014 USD ($) $ / shares	Nov. 01, 2014 USD ($)
Interest on senior convertible notes
Interest payable on Senior Convertible Debenture, beginning of period						$ 2,500		$ 2,500
Accrued interest expense				$ 2,747				9,885
Interest Payment on Senior Convertible Debenture								(7,416)
Interest payable on Senior Convertible Debenture, end of period			$ 2,500	4,969				4,969
Convertible Notes And Deferred Transaction Costs
Less: amortization				(1,544)				(4,060)
Conversions								(40,989)
Transactions Costs, end of period			12,336	8,276				8,276
Convertible Senior Notes Due 2019
Convertible Senior Notes
Aggregate principal amount (in dollars)		$ 200,000	200,000	177,787	$ 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 on Senior Convertible Debenture, beginning of period				2,222	6,250	2,500		2,500
Accrued interest expense				2,747	3,388	3,750	$ 0	9,900	$ 0
Interest Payment on Senior Convertible Debenture	$ (7,416)
Interest payable on Senior Convertible Debenture, end of period			2,500	$ 4,969	2,222	6,250		$ 4,969
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				6.0				13.2
Convertible Notes And Deferred Transaction Costs
Notes Balance, beginning of period			200,000	$ 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	167,967	188,281	187,664		187,664
Less: amortization			(411)	(1,544)	(1,899)	(617)	$ 0	(4,100)	$ 0
Conversions				(18,776)	(22,213)			(41,000)
Notes Balance, end of period		$ 200,000	200,000	159,011	177,787	200,000		159,011
Transactions Costs, end of period			12,336	8,276	9,820	11,719		8,276
Notes, net of Transaction Costs, end of period			$ 187,664	$ 150,735	$ 167,967	$ 188,281		$ 150,735