Stockholders' Equity (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	0 Months Ended	1 Months Ended	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2015	Mar. 31, 2015	Mar. 31, 2014	Feb. 28, 2014
Stockholders' Equity
Increase in total stockholders' equity			$ 211,200,000
Net proceeds from sale of common stock after deducting fees, commissions and other expenses related to offering		188,900,000
Increase in total stockholders' equity allocated to stock-based compensation expense			2,668,000	1,930,000
Increase in total stockholders' equity due to proceeds from exercise of stock options			6,719,000	1,017,000
Increase in total stockholders' equity partially offset by net loss			(12,904,000)	7,102,000
Common Stock Transactions
Number of shares sold in an underwritten public offering		4.6
Share price (in dollars per share)		$ 44.00	$ 44.00
Proceeds from the issuance of common stock		201,200,000	189,150,000
Underwriting discounts	12,100,000	12,100,000
Underwriting commissions and other offering expenses	$ 200,000	$ 200,000
Exercise price (in dollars per share)					$ 34.12