Investment Securities (Amortized Cost and Fair Value of Total Debt Securities) (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Disclosure Investment Securities Amortized Cost And Fair Value Of Total Debt Securities [Abstract]
Securities available for sale, Within one year - Amortized Cost	$ 33,572	$ 8,870
Securities available for sale, After one year but within five years - Amortized Cost	108,112	129,176
Securities available for sale, After five years but within ten years - Amortized Cost	909,907	945,637
Securities available for sale, After ten years - Amortized Cost	1,102,530	1,279,210
Securities available for sale - Amortized Cost	2,154,121	2,362,893
Securities available for sale, Within one year - Fair Value	34,014	9,005
Securities available for sale, After one year but within five years - Fair Value	110,911	130,091
Securities available for sale, After five years but within ten years - Fair Value	919,143	946,754
Securities available for sale, After ten years - Fair Value	1,104,113	1,265,682
Securities available for sale - Fair Value	$ 2,168,181	$ 2,351,532