FAIR VALUE - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Securities available for sale
Investment securities available for sale	$ 1,750,472	$ 1,881,920
Derivatives, included in assets:
Derivatives, included in assets	294	554
Derivatives, included in liabilities:
Derivatives, included in liabilities	221	753
Forward Contracts [Member]
Derivatives, included in liabilities:
Derivatives, included in liabilities	2	201
Equity Securities [Member]
Securities available for sale
Investment securities available for sale	418	408
U S Treasury Securities [Member]
Securities available for sale
Investment securities available for sale	7,432	7,509
Us Government Agencies Debt Securities Noncallable [Member]
Securities available for sale
Investment securities available for sale	364,859	356,919
Us Government Agencies Debt Securities Callable [Member]
Securities available for sale
Investment securities available for sale	1,353,262	1,469,463
US States And Political Subdivisions Member [Member]
Securities available for sale
Investment securities available for sale	6,771	26,828
Private Label Mbs [Member]
Securities available for sale
Investment securities available for sale	17,630	20,693
Interest Rate Cap [Member] | Purchase
Derivatives, included in assets:
Derivatives, included in assets	219	554
Interest Rate Cap [Member] | Written
Derivatives, included in liabilities:
Derivatives, included in liabilities	219	552
Forward And Future Contracts [Member] | Purchase
Derivatives, included in assets:
Derivatives, included in assets	75
Other Available For Sale Securities [Member]
Securities available for sale
Investment securities available for sale	100	100
Fair Value Inputs Level 1 [Member] | Forward Contracts [Member]
Derivatives, included in liabilities:
Derivatives, included in liabilities	0	0
Fair Value Inputs Level 1 [Member] | Equity Securities [Member]
Securities available for sale
Investment securities available for sale	418	408
Fair Value Inputs Level 1 [Member] | U S Treasury Securities [Member]
Securities available for sale
Investment securities available for sale	7,432	7,509
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] | Purchase
Derivatives, included in assets:
Derivatives, included in assets	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] | Forward Contracts [Member]
Derivatives, included in liabilities:
Derivatives, included in liabilities	2	201
Fair Value Inputs Level 2 [Member] | Equity 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	364,859	356,919
Fair Value Inputs Level 2 [Member] | Us Government Agencies Debt Securities Callable [Member]
Securities available for sale
Investment securities available for sale	1,353,262	1,469,463
Fair Value Inputs Level 2 [Member] | US States And Political Subdivisions Member [Member]
Securities available for sale
Investment securities available for sale	4,162	24,707
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	219	554
Fair Value Inputs Level 2 [Member] | Interest Rate Cap [Member] | Written
Derivatives, included in liabilities:
Derivatives, included in liabilities	219	552
Fair Value Inputs Level 2 [Member] | Forward And Future Contracts [Member] | Purchase
Derivatives, included in assets:
Derivatives, included in assets	75
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] | Forward Contracts [Member]
Derivatives, included in liabilities:
Derivatives, included in liabilities	0	0
Fair Value Inputs Level 3 [Member] | Equity 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	2,609	2,121
Fair Value Inputs Level 3 [Member] | Private Label Mbs [Member]
Securities available for sale
Investment securities available for sale	17,630	20,693
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] | Purchase
Derivatives, included in assets:
Derivatives, included in assets	0
Fair Value Inputs Level 3 [Member] | Other Available For Sale Securities [Member]
Securities available for sale
Investment securities available for sale	$ 100	$ 100