Mortgage Banking (Details) (USD $)	12 Months Ended
	Dec. 31, 2014 CPR	Dec. 31, 2013 CPR	Dec. 31, 2012
Mortgage servicing rights [Abstract]
Balance at beginning of period	$ 67,834,000	$ 47,341,000
Origination of servicing assets	12,293,000	18,481,000
Change in fair value:
Due to market changes	(7,202,000)	11,818,000
Due to runoff	(8,567,000)	(9,806,000)
Balance at end of period	64,358,000	67,834,000	47,341,000
Mortgage Loans on Real Estate [Line Items]
Total mortgage loans sold and serviced for others	5,636,249,000	5,460,676,000
Schedule of changes in the reserve for mortgage loan [Abstract]
Balance at beginning of period	1,050,000	7,800,000	4,277,000
Provision for putback expenses	600,000	1,561,000	8,015,000
Losses	(480,000)	(4,756,000)	(4,492,000)
FNMA resolution	0	(3,555,000)	0
Balance at end of period	1,170,000	1,050,000	7,800,000
Assumed average prepayment speed	11.51	9.72
Average discount rate (in hundredths)	10.29%	10.52%
Residential mortgage loans sold	913,500,000,000	1,358,000,000	1,816,000,000
Gains on sales of residential mortgage loans, before tax	10,800,000	26,400,000	33,900,000
Servicing fee income percentage of outstanding balance of underlying loans (in hundredths)	0.34%
Mortgage loans serviced for others	5,636,000,000	5,461,000,000
Period of putback response	60 days
Mortgage loan servicing representation and warranty expenses	600,000	1,600,000	8,000,000
Federal National Mortgage Association [Member]
Mortgage Loans on Real Estate [Line Items]
Total mortgage loans sold and serviced for others	3,579,987,000	3,499,659,000
Government National Mortgage Association [Member]
Mortgage Loans on Real Estate [Line Items]
Total mortgage loans sold and serviced for others	1,948,565,000	1,830,420,000
Federal Home Loan Mortgage Corporation [Member]
Mortgage Loans on Real Estate [Line Items]
Total mortgage loans sold and serviced for others	80,551,000	92,599,000
Other [Member]
Mortgage Loans on Real Estate [Line Items]
Total mortgage loans sold and serviced for others	$ 27,146,000	$ 37,998,000