Mortgage Servicing Rights (Details) - MSR - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Change in fair value of mortgage servicing rights
Balance, beginning of year	$ 43,580	$ 33,491	$ 61,968	$ 52,285	$ 52,285
Additions	5,939	10,416	8,429	20,309
Sales			(17,499)	(7,586)
Changes in fair value: Due to changes in model inputs or assumptions	(550)	1,413	(1,757)	(16,923)
Changes in fair value: Due to customer payoffs	(1,203)	(1,569)	(3,375)	(4,334)
Balance, end of year	47,766	$ 43,751	47,766	$ 43,751	61,968
Mortgage loans serviced for others	$ 4,175,195		$ 4,175,195		$ 5,480,943
MSR asset as a percentage of serviced mortgage loans	1.14%				1.13%
Key Assumptions
Weighted average constant prepayment rate (as a percent)			10.85%		10.47%
Weighted average discount rate (as a percent)			11.07%		10.95%
Weighted average life			6 years 10 months 24 days		6 years 10 months 24 days