Senior Convertible Notes (Details) $ / shares in Units, $ in Thousands, shares in Millions			1 Months Ended	2 Months Ended	3 Months Ended			6 Months Ended
	May. 01, 2015 USD ($)	Nov. 03, 2014 USD ($) $ / shares	Jun. 30, 2015 USD ($) shares	Dec. 31, 2014 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) shares	Jun. 30, 2014 USD ($)	Nov. 01, 2014 USD ($)
Interest on senior convertible notes
Interest payable on Senior Convertible Debenture, beginning of period						$ 2,500		$ 2,500
Accrued interest expense					$ 3,388			7,139
Interest Payment on Senior Convertible Debenture								(7,416)
Interest payable on Senior Convertible Debenture, end of period			$ 2,222	$ 2,500	2,222			2,222
Convertible Notes And Deferred Transaction Costs
Transaction Costs, Less: amortization					(1,899)			(2,516)
Notes Balance, Conversions								(22,213)
Transactions Costs, end of period			9,820	12,336	9,820			9,820
Convertible Senior Notes Due 2019
Convertible Senior Notes
Aggregate principal amount (in dollars)		$ 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					6,250	2,500		2,500
Accrued interest expense					3,388	3,750	$ 0	7,100	$ 0
Interest Payment on Senior Convertible Debenture	$ (7,416)
Interest payable on Senior Convertible Debenture, end of period			$ 2,222	2,500	2,222	6,250		$ 2,222
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			7.1					7.1
Convertible Notes And Deferred Transaction Costs
Notes Balance, beginning of period				200,000	200,000	200,000		$ 200,000
Transactions Costs, beginning of period										$ 12,747
Notes, net of Transaction Costs, beginning of period				187,253	188,281	187,664		187,664
Transaction Costs, Less: amortization				(411)	(1,899)	(617)	$ 0	(2,500)	$ 0
Notes Balance, Conversions			$ (22,200)		(22,213)			(22,200)
Notes Balance, end of period		$ 200,000	177,787	200,000	177,787	200,000		177,787
Transactions Costs, end of period			9,820	12,336	9,820	11,719		9,820
Notes, net of Transaction Costs, end of period			$ 167,967	$ 187,664	$ 167,967	$ 188,281		$ 167,967