Variable Interest Entities (Schedule of Non Consolidated Variable Interest Entities) (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Variable Interest Entity [Line Items]
Carrying Amount	$ 390,711	$ 422,723
Maximum Exposure to Loss	155,298	189,441
Trust Preferred Capital Securities Issuances [Member]
Variable Interest Entity [Line Items]
Carrying Amount	244,793	244,793
Maximum Exposure to Loss
Community Reinvestment Investments [Member]
Variable Interest Entity [Line Items]
Carrying Amount	1,810	1,447
Maximum Exposure to Loss	2,060	2,460
Commercial TDR Outstanding Loan Balance [Member]
Variable Interest Entity [Line Items]
Carrying Amount	144,025	176,312
Maximum Exposure to Loss	153,155	186,810
Commercial TDR Related Derivative Asset [Member]
Variable Interest Entity [Line Items]
Carrying Amount	83	171
Maximum Exposure to Loss	$ 83	$ 171