Investment Securities - Schedule of Maturities of Investment Securities Available-for-Sale (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost	$ 878,664	$ 850,699
Available-for-Sale, Fair Value	859,251	817,115
Within one year [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost	16,194	16,319
Available-for-Sale, Fair Value	16,233	16,378
After one year but within five years [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost	40,883	19,761
Available-for-Sale, Fair Value	41,046	19,986
After five years but within ten years [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost	294,552	229,033
Available-for-Sale, Fair Value	286,670	217,911
After ten years [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost	527,035	585,586
Available-for-Sale, Fair Value	$ 515,302	$ 562,840