Fair Value Measurements - Assets and Liabilities Measured on Recurring Basis (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 825,904	$ 803,600
Investment securities	100,083
Total assets	925,987	803,600
Total liabilities	0	0
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	825,904	803,600
Investment securities	100,083
Total assets	925,987	803,600
Total liabilities	0	0
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Investment securities	0
Total assets	0	0
Total liabilities	0	0
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Investment securities	0
Total assets	0	0
Total liabilities	$ 0	$ 0