Fair Value Measurements Fair Value Measurements - Assets and Liabilities Measured on a Recurring Basis (Details) - Recurring basis [Member] - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Carrying value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets - cash equivalents	$ 583,546	$ 465,388
Other assets	11,690	13,508
Estimate of Fair Value Measurement [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets - cash equivalents	583,546	465,388
Other assets	11,690	13,508
Estimate of Fair Value Measurement [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets - cash equivalents	0	0
Other assets	0	0
Estimate of Fair Value Measurement [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets - cash equivalents	0	0
Other assets	$ 0	$ 0