Fair Value Measurements - Recurring and Nonrecurring Basis (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities, Fair Value Disclosure	$ 31,662	$ 28,588
Available-for-sale Securities	9,974	7,420
Interest Rate Cash Flow Hedge Asset at Fair Value	14,515	11,622
Total	56,151	47,630
Interest Rate Cash Flow Hedge Liability at Fair Value	(177)	(580)
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities, Fair Value Disclosure	31,662	28,588
Available-for-sale Securities	0	0
Interest Rate Cash Flow Hedge Asset at Fair Value	0	0
Total	31,662	28,588
Interest Rate Cash Flow Hedge Liability at Fair Value	0	0
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities, Fair Value Disclosure	0	0
Available-for-sale Securities	9,974	7,420
Interest Rate Cash Flow Hedge Asset at Fair Value	14,515	11,622
Total	24,489	19,042
Interest Rate Cash Flow Hedge Liability at Fair Value	(177)	(580)
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities, Fair Value Disclosure	0	0
Available-for-sale Securities	0	0
Interest Rate Cash Flow Hedge Asset at Fair Value	0	0
Total	0	0
Interest Rate Cash Flow Hedge Liability at Fair Value	$ 0	$ 0