Senior Notes - Summary of Senior Notes (Details) - USD ($) $ in Millions	May 08, 2018	Jul. 14, 2010
May 2018 Senior Notes
Debt Instrument [Line Items]
Interest rate	5.25%
Maturity date	May 15, 2026
Series E
Debt Instrument [Line Items]
Amount		$ 60.0
Interest rate		4.72%
Maturity date		Jul. 14, 2016
Series F
Debt Instrument [Line Items]
Amount		$ 72.0
Interest rate		5.04%
Maturity date		Jul. 14, 2017
Series G
Debt Instrument [Line Items]
Amount		$ 28.0
Interest rate		5.42%
Maturity date		Jul. 14, 2019
Series H
Debt Instrument [Line Items]
Amount		$ 85.0
Interest rate		5.59%
Maturity date		Jul. 14, 2020

Contractual interest rate for funds borrowed, under the debt agreement.

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Carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion. Senior note holders are paid off in full before any payments are made to junior note holders.

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