Fair Value Measurements, Assets and Liabilities Measured at Fair Value Using Significant Unobservable Inputs (Level 3) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Investment Securities Available for Sale
Assets and Liabilities Measured at Fair Value Using Significant Unobservable Inputs (Level 3)
Beginning Balance	$ 200	$ 200	$ 200
Mortgage derivative gain (loss)		0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	(200)	(200)
Ending Balance		0	200
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Mortgage derivative gain (loss)		0	0
Derivative Financial Instruments
Assets and Liabilities Measured at Fair Value Using Significant Unobservable Inputs (Level 3)
Mortgage derivative gain (loss)		(1,889)	1,753
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		0
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning Balance	$ 3,114	3,114	1,361
Mortgage derivative gain (loss)		(1,889)	1,753
Ending Balance		$ 1,225	$ 3,114