Mortgage Banking Activities, Mortgage Servicing Rights (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Summary of Mortgage Servicing Rights [Abstract]
Number of residential mortgage loans serviced for others	120,653	117,483	107,660
Outstanding principal balance of residential mortgage loans serviced for others	$ 16,937,128,000	$ 16,162,887,000	$ 14,045,642,000
Weighted average interest rate (in hundredths)	4.24%	4.29%	4.38%
Remaining term (in months)	297 months	296 months	292 months
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	171,976,000		153,333,000
Additions, net	19,150,000		8,644,000
Change in fair value due to loan runoff	(7,553,000)		(3,742,000)
Change in fair value due to market changes	(8,522,000)		(4,461,000)
Ending balance	175,051,000	171,976,000	153,774,000
Servicing Assets at Fair Value, Assumptions Used to Estimate Fair Value [Abstract]
Discount rate - risk-free rate plus a market premium (in hundredths)	10.15%	10.17%	10.21%
Loan servicing costs - annually per loan based upon loan type, performing, minimum (in dollars per loan)	60	60	60
Loan servicing costs - annually per loan based upon loan type, performing, maximum (in dollars per loan)	105	105	105
Loan servicing costs - annually per loan based upon loan type, delinquent, minimum (in dollars per loan)	150	150	150
Loan servicing costs - annually per loan based upon loan type, delinquent, maximum (in dollars per loan)	500	500	500
Loan servicing costs - annually per loan based upon loan type, foreclosure, minimum (in dollars per loan)	1,000	1,000	1,000
Loan servicing costs - annually per loan based upon loan type, foreclosure, maximum (in dollars per loan)	4,250	4,250	4,250
Escrow earnings rate - indexed to rates paid on deposit accounts with comparable average life (in hundredths)	1.54%	1.77%	1.81%
Purchased [Member]
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	11,114,000		15,935,000
Additions, net	0		0
Change in fair value due to loan runoff	(781,000)		(515,000)
Change in fair value due to market changes	(740,000)		(630,000)
Ending balance	9,593,000		14,790,000
Originated [Member]
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	160,862,000		137,398,000
Additions, net	19,150,000		8,644,000
Change in fair value due to loan runoff	(6,772,000)		(3,227,000)
Change in fair value due to market changes	(7,782,000)		(3,831,000)
Ending balance	$ 165,458,000		$ 138,984,000