Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		12 Months Ended
	Aug. 31, 2015	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Jan. 31, 2016	May. 21, 2015	Nov. 11, 2014	Feb. 28, 2014
Stockholders' Equity
Increase in total stockholders' equity partially offset by debt issuance costs allocated to equity component of the Convertible Notes				$ (36,907)
Preferred Stock
Exercise price (in dollars per share)								$ 34.12
Common Stock Transactions
Number of shares sold in an underwritten public offering	3,600,000	4,600,000
Share price (in dollars per share)	$ 63.75	$ 44.00					$ 34.88
Proceeds from the issuance of common stock, net of underwriting discounts and other expenses	$ 218,600	$ 188,800	$ 407,477
Common stock, shares authorized			117,500,000	58,750,000		117,500,000
Prior to amendment
Common Stock Transactions
Common stock, shares authorized						58,750,000
Maximum
Common Stock Transactions
Share repurchase program, authorized amount (in shares)					$ 60,000
Rights [Member]
Preferred Stock
Exercise price (in dollars per share)			$ 80.00
Exercise price before adjustment (in dollars per share)			$ 250.00
Percentage of beneficial ownership to acquire to make the Rights exercisable			4.99%
Rights [Member] | Minimum
Preferred Stock
Percentage of ownership before the NOL Amendment			20.00%