Derivative and Other Fair Value Instruments - Summary of Consolidated Derivative Instruments (Details)	12 Months Ended
	Dec. 31, 2017 USD ($)
Fair Value Hedges [Member]
Derivative [Line Items]
Current Notional Balance	$ 450,000,000
Earliest Maturity Date	2019
Latest Maturity Date	2019
Fair Value Hedges [Member] | Minimum [Member]
Derivative [Line Items]
Interest Rate	2.375%
Fair Value Hedges [Member] | Maximum [Member]
Derivative [Line Items]
Interest Rate	2.375%
Forward Starting Swaps [Member]
Derivative [Line Items]
Current Notional Balance	$ 250,000,000
Earliest Maturity Date	2028
Latest Maturity Date	2029
Forward Starting Swaps [Member] | Minimum [Member]
Derivative [Line Items]
Interest Rate	2.1478%
Forward Starting Swaps [Member] | Maximum [Member]
Derivative [Line Items]
Interest Rate	2.2895%