Investment Securities (Amortized Cost and Fair Values of Investment Securities) (Detail) (USD $)	Jun. 30, 2014	Dec. 31, 2013
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	$ 2,167,716,000	$ 2,387,211,000
Available-for-Sale, Gross Unrealized Gains	41,232,000	28,103,000
Available-for-Sale, Gross Unrealized Losses	25,855,000	40,090,000
Total available-for-sale securities, Fair Value	2,183,093,000	2,375,224,000
U.S. Government Agencies [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	95,701,000	110,227,000
Available-for-Sale, Gross Unrealized Gains	276,000	343,000
Available-for-Sale, Gross Unrealized Losses	100,000	422,000
Total available-for-sale securities, Fair Value	95,877,000	110,148,000
Obligations Of States And Political Subdivisions [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	379,616,000	389,199,000
Available-for-Sale, Gross Unrealized Gains	20,922,000	13,386,000
Available-for-Sale, Gross Unrealized Losses	1,275,000	4,075,000
Total available-for-sale securities, Fair Value	399,263,000	398,510,000
Agency Residential Mortgage-Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	1,612,979,000	1,786,133,000
Available-for-Sale, Gross Unrealized Gains	18,363,000	12,163,000
Available-for-Sale, Gross Unrealized Losses	10,567,000	20,104,000
Total available-for-sale securities, Fair Value	1,620,775,000	1,778,192,000
Non-Agency Residential Mortgage-Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	385,000	572,000
Available-for-Sale, Gross Unrealized Gains	1,000	1,000
Available-for-Sale, Gross Unrealized Losses	5,000	8,000
Total available-for-sale securities, Fair Value	381,000	565,000
Commercial Mortgage Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	5,758,000	8,568,000
Available-for-Sale, Gross Unrealized Gains	124,000	166,000
Available-for-Sale, Gross Unrealized Losses	0	0
Total available-for-sale securities, Fair Value	5,882,000	8,734,000
Other Structured Financial Products [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	24,741,000	25,038,000
Available-for-Sale, Gross Unrealized Gains	0	0
Available-for-Sale, Gross Unrealized Losses	12,746,000	13,741,000
Total available-for-sale securities, Fair Value	11,995,000	11,297,000
Other Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	24,064,000	43,156,000
Available-for-Sale, Gross Unrealized Gains	847,000	1,487,000
Available-for-Sale, Gross Unrealized Losses	273,000	557,000
Total available-for-sale securities, Fair Value	24,638,000	44,086,000
Total Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	2,143,244,000	2,362,893,000
Available-for-Sale, Gross Unrealized Gains	40,533,000	27,546,000
Available-for-Sale, Gross Unrealized Losses	24,966,000	38,907,000
Total available-for-sale securities, Fair Value	2,158,811,000	2,351,532,000
Other Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	24,472,000	24,318,000
Available-for-Sale, Gross Unrealized Gains	699,000	557,000
Available-for-Sale, Gross Unrealized Losses	889,000	1,183,000
Total available-for-sale securities, Fair Value	$ 24,282,000	$ 23,692,000