Loan Servicing, Mortgage Origination, and Loans Held for Sale (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014	Dec. 31, 2014
Loans held for sale, loan servicing and mortgage origination
Residential mortgages serviced for others	$ 2,500,000	$ 2,200,000				$ 2,300,000
Contractually specified servicing fees earned	1,500	1,400	$ 300	$ 2,700
MSRs
Loans held for sale, loan servicing and mortgage origination
Mortgage servicing rights	25,325	21,015	21,601	20,729	$ 20,729	$ 21,601
Changes in the fair value of MSRs and its offsetting hedge
Increase (decrease) in fair value of MSRs	2,374	(483)	1,539	(692)
Decay of MSRs	(899)	(621)	(1,736)	(1,076)
Gains (losses) related to derivatives	(1,092)	1,140	430	1,935
Net effect on Statements of Income	383	36	233	167
Analysis of the activity in the MSRs
Balance at beginning of the period			21,601	20,729	20,729
Additions/(deductions):
Servicing assets that resulted from transfers of financial assets			3,921	2,054
Change in fair value due to valuation inputs or assumptions			1,539	(692)
Decay in fair value:
Due to increases in principal paydowns or runoff			(1,736)	(1,076)
Carrying value at end of period	$ 25,325	$ 21,015	$ 25,325	$ 21,015	$ 21,601
Characteristics and sensitivity analysis of the MSR
Residential Mortgages Serviced for Others Percentage	100.00%	100.00%				100.00%
Weighted average life			7 years 4 months 17 days	6 years 4 days	6 years 3 months 18 days
Constant prepayment rate (as a percent)			9.00%	12.10%	11.40%
Weighted average discount rate (as a percent)			9.70%	9.40%	9.70%
Effect on fair value due to change in interest rates:
25 basis point increase	$ 1,335	$ 1,311				$ 1,365
50 basis point increase	2,490	2,499				2,555
25 basis point decrease	(1,567)	(1,470)				(1,562)
50 basis point decrease	(3,313)	(2,736)				$ (3,221)
Custodial escrow balances maintained in connection with the loan servicing	$ 17,800	$ 15,600
Fixed-rate mortgage loans
Characteristics and sensitivity analysis of the MSR
Residential Mortgages Serviced for Others Percentage	99.30%	99.10%				99.20%
Adjustable-rate mortgage loans
Characteristics and sensitivity analysis of the MSR
Residential Mortgages Serviced for Others Percentage	0.70%	0.90%				0.80%