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Senior Notes - Principal Terms of Senior Notes Outstanding (Details) - Senior Notes | 12 Months Ended
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Dec. 31, 2018 USD ($)
2024 Senior Notes |  |
Debt Instrument |  |
Par value (in millions) | $ 400,000,000 | [1]
Stated coupon | 4.25% | [1]
Redemption price percentage | 100.00% |
2024 Senior Notes | Treasury Rate |  |
Debt Instrument |  |
Applicable basis spread over redemption price percentage | 0.25% |
2025 Senior Notes |  |
Debt Instrument |  |
Par value (in millions) | $ 350,000,000 | [1]
Stated coupon | 3.50% | [1]
Redemption price percentage | 100.00% |
2025 Senior Notes | Treasury Rate |  |
Debt Instrument |  |
Applicable basis spread over redemption price percentage | 0.25% |
[1] | The senior notes may be redeemed at any time, in whole or in part, at a make-whole redemption price plus accrued and unpaid interest.

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