Mortgage Banking Activities, Mortgage Servicing Rights (Details)	3 Months Ended			12 Months Ended
	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)
Summary of Mortgage Servicing Rights [Abstract]
Number of residential mortgage loans serviced for others	134,040	131,859	120,653	131,859
Outstanding principal balance of residential mortgage loans serviced for others	$ 20,294,662,000	$ 19,678,226,000	$ 16,937,128,000	$ 19,678,226,000
Weighted average interest rate (in hundredths)	4.10%	4.12%	4.24%	4.12%
Remaining term (in months)	300 months	300 months	297 months
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	$ 218,605,000		$ 171,976,000	$ 171,976,000
Additions, net	13,582,000		19,150,000
Change in fair value due to loan runoff	(8,144,000)		(7,553,000)
Change in fair value due to market changes	(27,988,000)		(8,522,000)
Ending balance	196,055,000	$ 218,605,000	175,051,000	218,605,000
Servicing Assets at Fair Value, Assumptions Used to Estimate Fair Value [Abstract]
Loan servicing costs - annually per loan based upon loan type, performing, minimum (in dollars per loan)	63		60	63
Loan servicing costs - annually per loan based upon loan type, performing, maximum (in dollars per loan)	120		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)	650		1,000	650
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)	1.19%	1.73%	1.54%
Primary secondary mortgage rate spread (in basis points)	120	130	138	130
Discount rate - risk-free rate plus a market premium (in hundredths)	10.11%	10.11%	10.15%
Purchased [Member]
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	$ 9,911,000		$ 11,114,000	$ 11,114,000
Additions, net	0		0
Change in fair value due to loan runoff	(626,000)		(781,000)
Change in fair value due to market changes	(3,336,000)		(740,000)
Ending balance	5,949,000	$ 9,911,000	9,593,000	9,911,000
Originated [Member]
Servicing Asset at Fair Value, Amount [Roll Forward]
Beginning balance	208,694,000		160,862,000	160,862,000
Additions, net	13,582,000		19,150,000
Change in fair value due to loan runoff	(7,518,000)		(6,772,000)
Change in fair value due to market changes	(24,652,000)		(7,782,000)
Ending balance	$ 190,106,000	$ 208,694,000	$ 165,458,000	$ 208,694,000