Fair Value of Financial Instruments - Auction rate securities and Contingent consideration (Details) - Significant Unobservable Inputs (Level 3) - Weighted Average - Discounted cash flow	9 Months Ended
	Sep. 30, 2017
Assets and liabilities measured at fair value on recurring basis
Quantitative information for Level 3 Fair Value Measurements Assets
Expected holding period	3 months
Estimated discount rate (as a percent)	12.00%
Auction rate securities
Quantitative information for Level 3 Fair Value Measurements Assets
Estimated yield (as a percent)	1.27%
Expected holding period	10 years
Estimated discount rate (as a percent)	3.27%