Summary of Significant Accounting Policies (Details) - Fair Values of the Companys Financial Instruments - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 200,772	$ 346,266
Available-for-sale securities	1,106	5,941
Total assets	201,878	352,207
Purchase consideration payable	4,994	4,967
Total liabilities	4,994	4,967
Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,100
Fair Value, Inputs, Level 1 [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	200,772	346,266
Available-for-sale securities	1,074	4,843
Total assets	201,846	351,109
Purchase consideration payable	0	0
Total liabilities	0	0
Fair Value, Inputs, Level 2 [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Available-for-sale securities	0	0
Total assets	0	0
Purchase consideration payable	0	0
Total liabilities	0	0
Fair Value, Inputs, Level 3 [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Available-for-sale securities	32	1,098
Total assets	32	1,098
Purchase consideration payable	4,994	4,967
Total liabilities	$ 4,994	$ 4,967