FAIR VALUE - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Securities available for sale
Investment securities available for sale	$ 1,974,226	$ 1,965,666
U S Treasury Securities [Member]
Securities available for sale
Investment securities available for sale	7,500	7,499
Us Government Agencies Debt Securities Noncallable [Member]
Securities available for sale
Investment securities available for sale	286,066	228,157
Us Government Agencies Debt Securities Callable [Member]
Securities available for sale
Investment securities available for sale	1,607,273	1,653,140
US States And Political Subdivisions Member [Member]
Securities available for sale
Investment securities available for sale	41,463	43,222
Private Label Mbs [Member]
Securities available for sale
Investment securities available for sale	31,824	33,648
Interest Rate Cap [Member] | Purchase
Derivatives, included in assets:
Derivatives, included in assets	1	6
Interest Rate Cap [Member] | Written
Derivatives, included in liabilities:
Derivatives, included in liabilities	1	6
Forward And Future Contracts [Member]
Derivatives, included in assets:
Derivatives, included in assets	0	0
Derivatives, included in liabilities:
Derivatives, included in liabilities	220	148
Interest Rate Swap [Member]
Derivatives, included in assets:
Derivatives, included in assets	0	33
Derivatives, included in liabilities:
Derivatives, included in liabilities	0	33
Other Available For Sale Securities [Member]
Securities available for sale
Investment securities available for sale	100	0
Fair Value Inputs Level 1 [Member] | U S Treasury Securities [Member]
Securities available for sale
Investment securities available for sale	7,500	7,499
Fair Value Inputs Level 1 [Member] | Us Government Agencies Debt Securities Noncallable [Member]
Securities available for sale
Investment securities available for sale	0	0
Fair Value Inputs Level 1 [Member] | Us Government Agencies Debt Securities Callable [Member]
Securities available for sale
Investment securities available for sale	0	0
Fair Value Inputs Level 1 [Member] | US States And Political Subdivisions Member [Member]
Securities available for sale
Investment securities available for sale	0	0
Fair Value Inputs Level 1 [Member] | Private Label Mbs [Member]
Securities available for sale
Investment securities available for sale	0	0
Fair Value Inputs Level 1 [Member] | Interest Rate Cap [Member] | Purchase
Derivatives, included in assets:
Derivatives, included in assets	0	0
Fair Value Inputs Level 1 [Member] | Interest Rate Cap [Member] | Written
Derivatives, included in liabilities:
Derivatives, included in liabilities	0	0
Fair Value Inputs Level 1 [Member] | Forward And Future Contracts [Member]
Derivatives, included in assets:
Derivatives, included in assets	0	0
Derivatives, included in liabilities:
Derivatives, included in liabilities		0
Fair Value Inputs Level 1 [Member] | Interest Rate Swap [Member]
Derivatives, included in assets:
Derivatives, included in assets	0	0
Derivatives, included in liabilities:
Derivatives, included in liabilities	0	0
Fair Value Inputs Level 1 [Member] | Other Available For Sale Securities [Member]
Securities available for sale
Investment securities available for sale	0	0
Fair Value Inputs Level 2 [Member] | U S Treasury Securities [Member]
Securities available for sale
Investment securities available for sale	0	0
Fair Value Inputs Level 2 [Member] | Us Government Agencies Debt Securities Noncallable [Member]
Securities available for sale
Investment securities available for sale	286,066	228,157
Fair Value Inputs Level 2 [Member] | Us Government Agencies Debt Securities Callable [Member]
Securities available for sale
Investment securities available for sale	1,607,273	1,653,140
Fair Value Inputs Level 2 [Member] | US States And Political Subdivisions Member [Member]
Securities available for sale
Investment securities available for sale	39,073	40,658
Fair Value Inputs Level 2 [Member] | Private Label Mbs [Member]
Securities available for sale
Investment securities available for sale	0	0
Fair Value Inputs Level 2 [Member] | Interest Rate Cap [Member] | Purchase
Derivatives, included in assets:
Derivatives, included in assets	1	6
Fair Value Inputs Level 2 [Member] | Interest Rate Cap [Member] | Written
Derivatives, included in liabilities:
Derivatives, included in liabilities	1	6
Fair Value Inputs Level 2 [Member] | Forward And Future Contracts [Member]
Derivatives, included in assets:
Derivatives, included in assets	0	0
Derivatives, included in liabilities:
Derivatives, included in liabilities	220	148
Fair Value Inputs Level 2 [Member] | Interest Rate Swap [Member]
Derivatives, included in assets:
Derivatives, included in assets	0	33
Derivatives, included in liabilities:
Derivatives, included in liabilities	0	33
Fair Value Inputs Level 2 [Member] | Other Available For Sale Securities [Member]
Securities available for sale
Investment securities available for sale	0	0
Fair Value Inputs Level 3 [Member] | U S Treasury Securities [Member]
Securities available for sale
Investment securities available for sale	0	0
Fair Value Inputs Level 3 [Member] | Us Government Agencies Debt Securities Noncallable [Member]
Securities available for sale
Investment securities available for sale	0	0
Fair Value Inputs Level 3 [Member] | Us Government Agencies Debt Securities Callable [Member]
Securities available for sale
Investment securities available for sale	0	0
Fair Value Inputs Level 3 [Member] | US States And Political Subdivisions Member [Member]
Securities available for sale
Investment securities available for sale	2,390	2,564
Fair Value Inputs Level 3 [Member] | Private Label Mbs [Member]
Securities available for sale
Investment securities available for sale	31,824	33,648
Fair Value Inputs Level 3 [Member] | Interest Rate Cap [Member] | Purchase
Derivatives, included in assets:
Derivatives, included in assets	0	0
Fair Value Inputs Level 3 [Member] | Interest Rate Cap [Member] | Written
Derivatives, included in liabilities:
Derivatives, included in liabilities	0	0
Fair Value Inputs Level 3 [Member] | Forward And Future Contracts [Member]
Derivatives, included in assets:
Derivatives, included in assets	0	0
Derivatives, included in liabilities:
Derivatives, included in liabilities	0	0
Fair Value Inputs Level 3 [Member] | Interest Rate Swap [Member]
Derivatives, included in assets:
Derivatives, included in assets	0	0
Derivatives, included in liabilities:
Derivatives, included in liabilities	0	0
Fair Value Inputs Level 3 [Member] | Other Available For Sale Securities [Member]
Securities available for sale
Investment securities available for sale	$ 100	$ 0