Fair Value of Financial Instruments Fair Value of Financial Instruments, Reconciliation of Level 3 Securities (Details) - USD ($) $ in Thousands |
9 Months Ended | ||||
---|---|---|---|---|---|
Sep. 30, 2017 |
Sep. 30, 2016 |
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Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] | |||||
Beginning balance, January 1 | $ 2,552,600 | ||||
Transfers (out) of Level 3 (1) | (7,000) | [1] | $ 0 | ||
Purchases and sales, net | (200) | 4,900 | |||
Ending balance, September 30 | 2,624,800 | ||||
Fair Value, Inputs, Level 3 [Member] | |||||
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] | |||||
Beginning balance, January 1 | 11,900 | 0 | |||
Ending balance, September 30 | $ 4,700 | $ 4,900 | |||
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