Fair Value Measurements - Narrative (Details) € in Millions			9 Months Ended
	Oct. 05, 2015 EUR (€)	Oct. 05, 2015 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)
Cash and Cash Equivalents [Line Items]
Unrealized gains on the investments after-tax			$ 451,000	$ 471,000
Money market funds
Cash and Cash Equivalents [Line Items]
Unrealized gains on the investments			0
Other mutual funds
Cash and Cash Equivalents [Line Items]
Unrealized gains on the investments			700,000	800,000
Fair Value, Measurements, Recurring
Cash and Cash Equivalents [Line Items]
Assets, Fair Value Disclosure			9,681,000	11,054,000
Fair Value, Measurements, Recurring | Money market funds
Cash and Cash Equivalents [Line Items]
Assets, Fair Value Disclosure			7,519,000	8,518,000
Fair Value, Measurements, Recurring | Other mutual funds
Cash and Cash Equivalents [Line Items]
Assets, Fair Value Disclosure			2,162,000	$ 2,536,000
N200 Limited and Affiliates
Cash and Cash Equivalents [Line Items]
Increase in contingent liability			$ 100,000
Subsequent Event | N200 Limited and Affiliates
Cash and Cash Equivalents [Line Items]
Payment of contingent liability	€ 1.0	$ 1,100,000