Mortgage Servicing Rights - At Amortized Cost (Details) (Mortgage loans, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Mortgage loans
Servicing Asset at Amortized Value, Balance [Roll Forward]
Servicing asset at amortized cost, before valuation reserve, beginning	$ 13,450	$ 13,811	$ 18,732
Sales of mortgage servicing rights	(735)	0	(4,528)
Purchases of mortgage servicing rights	0	0	0
Originations of mortgage servicing rights	4,563	2,864	4,222
Amorization expense	3,501	3,225	4,615
Write-off of permanent impairment	(553)	0	0
Servicing asset at amortized cost, before valuation reserve, ending	13,224	13,450	13,811
Less valuation reserve	(571)	(1,895)	(620)
Servicing asset at fair value, ending	12,653	11,555	13,191
Principal balance of serviced loans underlying mortgage servicing rights	2,146,351	1,803,303	1,594,697
Mortgage servicing rights as a percentage of serviced loans	0.0059	0.0064	0.0083
Disclosure of Transfer of Securitizations or Asset-backed Financing Financial Assets Accounted for as Sale [Abstract]
Carrying value of sold mortgage servicing rights	735		4,528
Losses on sale of mortgage servicing rights recorded as other expense	$ (19)		$ 1,525