Derivatives - Schedule Summarizing Terms of Entity's Derivative Financial Instruments (Details)	Dec. 31, 2017 USD ($)
Derivative [Line Items]
Notional amounts	$ 2,154,799,000
Cash Flow Hedging | Swap Agreements | Minimum
Derivative [Line Items]
Notional amounts	$ 4,873,000
Strike rate	1.13%
Cash Flow Hedging | Swap Agreements | Maximum
Derivative [Line Items]
Notional amounts	$ 267,431,000
Strike rate	3.84%