Low-Income Housing Tax Credits (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) Fund	Dec. 31, 2016 USD ($) Fund	Dec. 31, 2015 USD ($)
Low-Income Housing Tax Credits [Abstract]
Number of housing equity funds | Fund	4	4
Low-income housing investment	$ 3,500	$ 3,900
Additional committed capital calls expected	1,100	2,500
Amortization expense	340	300	$ 219
Tax credits and other tax benefits [Abstract]
Tax credits received	412	384	(291)
Tax benefit from losses	116	102	74
Total tax benefit	$ 528	$ 486	$ 365