Fair Value Measurements - Additional Information (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Cash and Cash Equivalents [Line Items]
Unrealized gains on the investments after-tax	$ 471,000	$ 429,000
Money market funds
Cash and Cash Equivalents [Line Items]
Assets, Fair Value Disclosure	8,500,000	100,000
Accumulated Gross Unrealized Gain	0	0
Other mutual funds
Cash and Cash Equivalents [Line Items]
Assets, Fair Value Disclosure	2,500,000	2,000,000
Accumulated Gross Unrealized Gain	800,000	700,000
Unrealized gains on the investments after-tax	$ 500,000	$ 400,000