Mortgage Banking Activities, Components of Loans Held For Sale (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Schedule of Residential Mortgage Loans Held For Sale [Line Items]
Number of days for past due for loan to be considered nonperforming (in days)	90 days	90 days	90 days
Residential mortgage loans held for sale, nonperforming	$ 0	$ 0	$ 0
Credit losses recognized on residential mortgage loans held for sale	0	0	0
Components of Residential Mortgage Loans Held for Sale [Abstract]
Unpaid principal balance	215,803	237,811	212,525
Residential mortgage loans held for sale, Fair value	217,022	237,695	215,113
Total residential mortgage loans held for sale and mortgage loan commitments, net of forward sales contracts	$ 225,190	$ 248,707	$ 221,378
Residential Mortgage Loan Commitments [Member] | Not Designated as Hedging Instrument [Member]
Schedule of Residential Mortgage Loans Held For Sale [Line Items]
General number of days outstanding for residential mortgage commitments, minimum (in days)	60 days	60 days	60 days
General number of days outstanding for residential mortgage commitments, maximum (in days)	90 days	90 days	90 days
Components of Residential Mortgage Loans Held for Sale [Abstract]
Notional	$ 298,318	$ 381,732	$ 222,919
Derivative, Net fair value	$ 8,597	$ 14,267	$ 6,523
Forward sales contracts [Member] | Not Designated as Hedging Instrument [Member]
Schedule of Residential Mortgage Loans Held For Sale [Line Items]
General number of days for delivery of loans, for which the price is set by forward sales contracts, minimum (in days)	60 days	60 days	60 days
General number of days for delivery for loans, for which the price is set by forward sales contracts, maximum (in days)	90 days	90 days	90 days
Components of Residential Mortgage Loans Held for Sale [Abstract]
Notional	$ 432,812	$ 586,517	$ 380,159
Derivative, Net fair value	$ (429)	$ (3,255)	$ (258)