Mergers and Acquisitions - Northern Hancock Bank & Trust Co., Estimated Fair Value of Assets Acquired and Liabilities Assumed (Details) (Details) - USD ($) $ in Thousands		12 Months Ended
	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Consideration paid:
Gain on bargain purchase		$ 1,316	$ 0
Northern Hancock
Business Acquisition [Line Items]
Cash and cash equivalents	$ 2,539
Loans receivable	18,480
Federal bank stocks	11
Accrued interest receivable	103
Premises and equipment	708
Core deposit intangible	167
Prepaid expenses and other assets	766
Total assets acquired	22,774
Deposits	19,748
Accrued interest payable	6
Accrued expenses and other liabilities	8
Total liabilities assumed	19,762
Identifiable net assets acquired	3,012
Consideration paid:
Cash	22
Common stock	1,674
Total consideration	1,696
Gain on bargain purchase	$ 1,316