Senior Convertible Notes - Schedule of Activity and Balances Associated with the Notes and Related Deferred Transaction Costs (Details) - USD ($) $ in Thousands		2 Months Ended	3 Months Ended							9 Months Ended
	Mar. 18, 2016	Dec. 31, 2014	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Sep. 30, 2016	Sep. 30, 2015
Convertible Notes And Deferred Transaction Costs[Roll forward]
Less: amortization										$ (4,658)	$ (4,060)
Conversions										(82,274)	(40,989)
Convertible Senior Notes Due 2019
Convertible Notes And Deferred Transaction Costs[Roll forward]
Notes Balance, beginning of period		$ 200,000	$ 79,182	$ 79,182	$ 159,011	$ 159,011	$ 177,787	$ 200,000	$ 200,000	159,011	200,000
Deferred Debt Costs, beginning of period		12,747	3,364	3,617	7,770	8,276	9,820	11,719	12,336	7,770	12,336
Notes, net of Debt Costs, beginning of period		187,253	75,818	75,565	151,241	150,735	167,967	188,281	187,664	151,241	187,664
Less: amortization	$ (3,600)	(411)	(252)	(253)	(4,153)	(506)	(1,544)	(1,899)	(617)	(4,700)	(4,100)
Conversions	$ (79,800)				(79,829)		(18,776)	(22,213)
Notes Balance, end of period		200,000	79,182	79,182	79,182	159,011	159,011	177,787	200,000	79,182	159,011
Deferred Debt Costs, end of period		12,336	3,112	3,364	3,617	7,770	8,276	9,820	11,719	3,112	8,276
Notes, net of Debt Costs, end of period		$ 187,664	$ 76,070	$ 75,818	$ 75,565	$ 151,241	$ 150,735	$ 167,967	$ 188,281	$ 76,070	$ 150,735