Goodwill and Intangible Assets, Mortgage Servicing Rights Roll-Forward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Mortgage servicing rights:
Mortgage servicing rights at beginning of year	$ 59,168	$ 62,085	$ 62,150
Additions from acquisition	8,136	0	0
Additions	10,722	7,167	12,262
Amortization	(9,594)	(10,084)	(12,327)
Mortgage servicing rights at end of year	68,433	59,168	62,085
Valuation Allowance for Impairment of Recognized Servicing Assets [Roll Forward]
Valuation allowance at beginning of year	(784)	(609)	(809)
(Additions) recoveries, net	545	(175)	200
Valuation allowance at end of year	(239)	(784)	(609)
Mortgage servicing rights, net	68,193	58,384	61,476
Fair value of mortgage servicing rights	81,012	64,387	73,149
Portfolio of residential mortgage loans serviced for others (“servicing portfolio”)	$ 8,600,983	$ 7,646,846	$ 7,974,742
Mortgage servicing rights, net to servicing portfolio	0.79%	0.76%	0.77%
Mortgage servicing rights expense (a)	$ 9,049	$ 10,259	$ 12,127