Fair Value of Financial Instruments - Summary of Investments and Cash Equivalents (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
U.S. government and agency securities maturing within one year	$ 68,300
U.S. government and agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	85,249	$ 109,136
Gross Unrealized Gain	37	3
Gross Unrealized Loss	0	(52)
Estimated Fair Value	$ 85,286	$ 109,087