Fair Value of Financial Instruments - Summary of Investments and Cash Equivalents (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
U.S. government and agency securities maturing within one year	$ 79,500,000
U.S. government and agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	97,926,000	109,136,000
Gross Unrealized Gain	12,000	3,000
Gross Unrealized Loss	(6,000)	(52,000)
Estimated Fair Value	$ 97,932,000	$ 109,087,000