Fair Value Disclosures - Fair Value of Nonfinancial Assets (Details) - USD ($) $ in Thousands |
3 Months Ended | 6 Months Ended | 12 Months Ended | |||
---|---|---|---|---|---|---|
Jun. 30, 2018 |
Jun. 30, 2017 |
Jun. 30, 2018 |
Jun. 30, 2017 |
Dec. 31, 2017 |
Jan. 01, 2018 |
|
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] | ||||||
Impairment Charge | $ 0 | $ 234 | $ 0 | $ 267 | $ 854 | |
Fair Value Net of Impairment | 3,247,786 | 3,247,786 | 3,105,553 | $ 3,056,236 | ||
Fair Value [Member] | Nonrecurring [Member] | ||||||
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] | ||||||
Fair Value Net of Impairment | $ 0 | $ 0 | $ 12,950 |