Investment Securities (Gross Unrealized Losses and Fair Values by Investment and Length of Time Of Securities) (Detail) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Schedule Of Available For Sale Securities [Line Items]
Fair Value, Less than 12 Months	$ 318,926,000	$ 1,192,634,000
Unrealized Losses, Less than 12 Months	2,193,000	24,730,000
Fair Value, 12 Months or More	390,307,000	26,417,000
Unrealized Losses, 12 Months or More	23,446,000	15,360,000
Fair Value, Total	709,233,000	1,219,051,000
Unrealized Losses, Total	25,639,000	40,090,000
U.S. Government Agencies [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value, Less than 12 Months	36,477,000	68,111,000
Unrealized Losses, Less than 12 Months	83,000	422,000
Fair Value, 12 Months or More	1,952,000	0
Unrealized Losses, 12 Months or More	48,000	0
Fair Value, Total	38,429,000	68,111,000
Unrealized Losses, Total	131,000	422,000
Obligations Of States And Political Subdivisions [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value, Less than 12 Months	0	73,895,000
Unrealized Losses, Less than 12 Months	0	3,910,000
Fair Value, 12 Months or More	52,383,000	7,025,000
Unrealized Losses, 12 Months or More	657,000	165,000
Fair Value, Total	52,383,000	80,920,000
Unrealized Losses, Total	657,000	4,075,000
Agency Residential Mortgage-Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value, Less than 12 Months	280,503,000	1,030,987,000
Unrealized Losses, Less than 12 Months	2,107,000	20,104,000
Fair Value, 12 Months or More	317,208,000	0
Unrealized Losses, 12 Months or More	8,950,000	0
Fair Value, Total	597,711,000	1,030,987,000
Unrealized Losses, Total	11,057,000	20,104,000
Non-Agency Residential Mortgage-Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value, Less than 12 Months	0	530,000
Unrealized Losses, Less than 12 Months	0	8,000
Fair Value, 12 Months or More	278,000	0
Unrealized Losses, 12 Months or More	4,000	0
Fair Value, Total	278,000	530,000
Unrealized Losses, Total	4,000	8,000
Commercial Mortgage Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value, Less than 12 Months	1,946,000
Unrealized Losses, Less than 12 Months	3,000
Fair Value, 12 Months or More	0
Unrealized Losses, 12 Months or More	0
Fair Value, Total	1,946,000
Unrealized Losses, Total	3,000
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	11,761,000	11,297,000
Unrealized Losses, 12 Months or More	12,801,000	13,741,000
Fair Value, Total	11,761,000	11,297,000
Unrealized Losses, Total	12,801,000	13,741,000
Other Debt Securities [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	5,148,000	6,476,000
Unrealized Losses, 12 Months or More	98,000	557,000
Fair Value, Total	5,148,000	6,476,000
Unrealized Losses, Total	98,000	557,000
Other Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value, Less than 12 Months	0	19,111,000
Unrealized Losses, Less than 12 Months	0	286,000
Fair Value, 12 Months or More	1,577,000	1,619,000
Unrealized Losses, 12 Months or More	888,000	897,000
Fair Value, Total	1,577,000	20,730,000
Unrealized Losses, Total	$ 888,000	$ 1,183,000