Basis of Presentation and Significant Accounting Policies (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018 Bank	Dec. 31, 2017 USD ($)	[1]	Dec. 31, 2016 USD ($)	[2]
Accounting Policies [Abstract]
Number of banks through which company operates (in bank) | Bank	1
Number of regional banking units Chemical Bank operates through (in bank) | Bank	7
Business Acquisition
Cumulative effect adjustment of change in accounting policy, net of tax impact | $		$ 1,339		$ 3,659
Retained earnings
Business Acquisition
Cumulative effect adjustment of change in accounting policy, net of tax impact | $		$ 1,680		$ 3,659

[1] Refer to Note 1, Basis of Presentation and Significant Accounting Policies, Note 3, Investment Securities, Note 5, Other Real Estate Owned and Repossessed Assets and Note 9, Derivative Instruments and Balance Sheet Offsetting, for further details on the changes in accounting policy.

[2] Refer to Note 1, Basis of Presentation and Significant Accounting Policies and Note 7, Loan Servicing Rights for further details on the changes in accounting policy.