Allowance for Credit Losses Schedule of Loans Outstanding and Past Due (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Recorded Investment, 30 to 59 Days Past Due	$ 114,027		$ 107,245
Financing Receivable, Recorded Investment, 60 to 89 Days Past Due	37,140		36,548
Financing Receivable, Recorded Investment, Equal to Greater than 90 Days Past Due	109,632		115,003
Financing Receivable, Recorded Investment, Past Due	260,799		258,796
Financing Receivable, Recorded Investment, Current	6,993,033		7,317,081
Total recorded investment	7,253,832		7,575,877
Mortgage Loans In Process Of Foreclosure	77,828	[1]	82,859	[1]
Loans and Leases Receivable, Serious Delinquencies Ratio	1.52%	[2]	1.52%	[2]
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	109,390	[3]	114,761	[3]
Financing Receivable, Recorded Investment, Nonaccrual Status	2,922		2,538
Financing Receivable, Modifications, Recorded Investment	6,219		5,249
Conventional Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Recorded Investment, 30 to 59 Days Past Due	54,933		47,189
Financing Receivable, Recorded Investment, 60 to 89 Days Past Due	18,547		18,103
Financing Receivable, Recorded Investment, Equal to Greater than 90 Days Past Due	72,038		77,113
Financing Receivable, Recorded Investment, Past Due	145,518		142,405
Financing Receivable, Recorded Investment, Current	6,174,006		6,433,700
Total recorded investment	6,319,524		6,576,105
Mortgage Loans In Process Of Foreclosure	61,530	[1]	67,016	[1]
Loans and Leases Receivable, Serious Delinquencies Ratio	1.15%	[2]	1.17%	[2]
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	71,796	[3]	76,871	[3]
Financing Receivable, Recorded Investment, Nonaccrual Status	2,922		2,538
Federal Housing Administration Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Recorded Investment, 30 to 59 Days Past Due	59,094		60,056
Financing Receivable, Recorded Investment, 60 to 89 Days Past Due	18,593		18,445
Financing Receivable, Recorded Investment, Equal to Greater than 90 Days Past Due	37,594		37,890
Financing Receivable, Recorded Investment, Past Due	115,281		116,391
Financing Receivable, Recorded Investment, Current	819,027		883,381
Total recorded investment	934,308		999,772
Mortgage Loans In Process Of Foreclosure	16,298	[1]	15,843	[1]
Loans and Leases Receivable, Serious Delinquencies Ratio	4.04%	[2]	3.82%	[2]
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	37,594	[3]	37,890	[3]
Financing Receivable, Recorded Investment, Nonaccrual Status	$ 0		$ 0

[1] Includes loans where the decision of foreclosure or a similar alternative such as pursuit of deed-in-lieu has been reported. Loans in process of foreclosure are included in past due or current loans dependent on their delinquency status.

[2] Loans that are 90 days or more past due or in the process of foreclosure (including past due or current loans in the process of foreclosure) expressed as a percentage of the total loan portfolio class recorded investment amount.

[3] Each conventional loan past due 90 days or more still accruing interest is on a schedule/scheduled monthly settlement basis and contains one or more credit enhancements. Loans that are well secured and in the process of collection as a result of remaining credit enhancements and schedule/scheduled settlement are not placed on non-accrual status.