Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended		3 Months Ended		9 Months Ended
	Aug. 05, 2015	May. 21, 2015	Aug. 31, 2015	Mar. 31, 2015	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Equity compensation plans
Common Stock, Shares Authorized		117,500,000			117,500,000		117,500,000		58,750,000
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
Proceeds from the issuance of common stock, net of underwriting discounts and other expenses	$ 218,600		$ 218,600	$ 188,800			$ 407,477
Increase in total stockholders' equity							460,000
Net income (loss)					$ (20,584)	$ 1,458	25,578	$ (7,191)
Increase in total stockholders' equity due to proceeds from exercise of stock options							15,482	2,909
Increase in total stockholders' equity allocated to stock-based compensation expense							$ 11,572	$ 6,153
Prior to amendment
Equity compensation plans
Common Stock, Shares Authorized		58,750,000
Equity Incentive Plan 2007
Equity compensation plans
Additional shares authorized for issuance		1,700,000