Stockholders' Equity and Convertible Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands			12 Months Ended
	Jul. 28, 2015	Jan. 28, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Class of stock
Shares sold (in shares)		4,000,000
Share issue price (in dollars per share)		$ 36.75
Aggregate proceeds received, net of underwriting discounts and commissions and offering costs		$ 158,400
Proceeds from the sale of common stock		$ 137,800	$ 0	$ 0	$ 482,250
Outstanding warrants			605,415	630,444
Underwriters
Class of stock
Options exercised by underwriters (in shares)		600,000
Minimum
Class of stock
Exercise price of warrants (in dollars per share)			$ 14.00	$ 14.00
Maximum
Class of stock
Exercise price of warrants (in dollars per share)			$ 16.97	$ 16.97
Common Stock
Class of stock
Shares sold (in shares)	4,054,054
Share issue price (in dollars per share)	$ 74.00
Aggregate proceeds received, net of underwriting discounts and commissions and offering costs	$ 323,800
Proceeds from the sale of common stock	$ 281,500
Common Stock | Underwriters
Class of stock
Options exercised by underwriters (in shares)	608,108