Derivative Instruments (Effect of Derivatives on Consolidated Statements of Income (Details) - Designated as Hedging Instrument [Member] - Interest rate contracts [Member] - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Fair Value Hedging [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized gain (loss) on interest rate contracts	[1]	$ (36)	$ 167
Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Loss recognized in other comprehensive income, net of tax (effective portion)		(992)	(2)
Cash Flow Hedging [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Loss reclassified from accumulated other comprehensive income (effective portion)	[1]	$ (2)	$ (50)

[1] Realized gain (loss) on hedging instruments consists of net cash settlements and interest accruals on the fair value interest rate swaps during the periods. Net cash settlements are included in the supplemental cash flow information within interest, net of amounts capitalized in the Condensed Consolidated Statements of Cash Flows