Summary of Significant Accounting Policies (Details) - Fair Values of the Companys Financial Instruments - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 156,294	$ 346,266
Available-for-sale securities	1,480	5,941
Total assets	157,774	352,207
Purchase consideration payable	4,981	4,967
Total liabilities	4,981	4,967
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	156,294	346,266
Available-for-sale securities	0	4,843
Total assets	156,294	351,109
Purchase consideration payable	0	0
Total liabilities	0	0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, 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
Total assets	0	0
Purchase consideration payable	0	0
Total liabilities	0	0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, 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	1,480	1,098
Total assets	1,480	1,098
Purchase consideration payable	4,981	4,967
Total liabilities	$ 4,981	$ 4,967