Investment Securities (Gross Unrealized Losses and Fair Values by Investment and Length of Time Of Securities) (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Schedule Of Available For Sale Securities [Line Items]
Fair Value, Less than 12 Months	$ 1,064,132	$ 56,950
Unrealized Losses, Less than 12 Months	18,555	1,383
Fair Value, 12 Months or More	39,414	31,548
Unrealized Losses, 12 Months or More	16,659	17,627
Fair Value, Total	1,103,546	88,498
Unrealized Losses, Total	35,214	19,010
U.S. Government Agencies [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value, Less than 12 Months	42,890	0
Unrealized Losses, Less than 12 Months	535	0
Fair Value, 12 Months or More	0	0
Unrealized Losses, 12 Months or More	0	0
Fair Value, Total	42,890	0
Unrealized Losses, Total	535	0
Obligations Of States And Political Subdivisions [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value, Less than 12 Months	74,856	31,791
Unrealized Losses, Less than 12 Months	3,959	295
Fair Value, 12 Months or More	7,051	0
Unrealized Losses, 12 Months or More	199	0
Fair Value, Total	81,907	31,791
Unrealized Losses, Total	4,158	295
Agency Residential Mortgage-Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value, Less than 12 Months	928,206	11,291
Unrealized Losses, Less than 12 Months	13,856	53
Fair Value, 12 Months or More	0	0
Unrealized Losses, 12 Months or More	0	0
Fair Value, Total	928,206	11,291
Unrealized Losses, Total	13,856	53
Non-Agency Residential Mortgage-Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value, Less than 12 Months	11,501	12,117
Unrealized Losses, Less than 12 Months	137	450
Fair Value, 12 Months or More	13,641	14,683
Unrealized Losses, 12 Months or More	610	1,530
Fair Value, Total	25,142	26,800
Unrealized Losses, Total	747	1,980
Other Structured Financial Products [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value, Less than 12 Months	0	0
Unrealized Losses, Less than 12 Months	0	0
Fair Value, 12 Months or More	10,506	9,551
Unrealized Losses, 12 Months or More	14,543	15,461
Fair Value, Total	10,506	9,551
Unrealized Losses, Total	14,543	15,461
Other Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value, Less than 12 Months	6,679	0
Unrealized Losses, Less than 12 Months	68	0
Fair Value, 12 Months or More	6,606	6,518
Unrealized Losses, 12 Months or More	402	464
Fair Value, Total	13,285	6,518
Unrealized Losses, Total	470	464
Other Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value, Less than 12 Months	0	1,751
Unrealized Losses, Less than 12 Months	0	585
Fair Value, 12 Months or More	1,610	796
Unrealized Losses, 12 Months or More	905	172
Fair Value, Total	1,610	2,547
Unrealized Losses, Total	$ 905	$ 757