Allowances for Loan Losses - Additional Information Regarding Methods used to Evaluate Loan Portfolio for Impairment (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans individually evaluated for impairment	$ 73,636	$ 116,385
Loans collectively evaluated for impairment	32,158,945	29,705,330
Acquired loans with deteriorated credit quality	2,504,622	2,788,618
Total	34,737,203	32,610,333
Mortgage Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans individually evaluated for impairment	66,923	109,389
Loans collectively evaluated for impairment	31,171,683	28,859,599
Acquired loans with deteriorated credit quality	2,282,064	2,529,200
Total	33,520,670	31,498,188
Other loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans individually evaluated for impairment	6,713	6,996
Loans collectively evaluated for impairment	987,262	845,731
Acquired loans with deteriorated credit quality	222,558	259,418
Total	$ 1,216,533	$ 1,112,145