FAIR VALUE MEASUREMENTS - Assets and Liabilities on Recurring Basis (Detail) - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		$ 3,002,787
Assets measured at fair value, securities available for sale		3,002,787	$ 2,764,562
Loans held for sale	[1]	28,213	56,458
Derivative assets		20,887	30,547
Derivative liabilities		66,443	29,197
US Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		95,526
U.S. Government-Sponsored Entities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		306,934	343,942
Agency Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		831,817	794,957
Assets measured at fair value, securities available for sale		831,817
Non-Agency Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		0	1
Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		168,324
Assets measured at fair value, securities available for sale		168,324
States of the U.S. and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		20,735	21,093
Other Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		1,855	4,670
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, securities available for sale		0	161
Derivative assets		0	0
Derivative liabilities		0	0
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, securities available for sale		3,002,787	2,764,401
Derivative assets		19,225	28,953
Derivative liabilities		66,436	29,192
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value, securities available for sale		0	0
Derivative assets		1,662	1,594
Derivative liabilities		7	5
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		3,002,787	2,763,537
Equity securities		1,172	1,025
Assets measured at fair value, securities available for sale			2,764,562
Loans held for sale		28,213	56,458
Derivative assets		20,887	30,547
Assets measured at fair value on a recurring basis, Total		3,053,059	2,851,567
Derivative liabilities		66,443	29,197
Liabilities measured at fair value on a recurring basis, Total		66,443	29,197
Fair Value, Measurements, Recurring [Member] | Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities		61,728	26,953
Fair Value, Measurements, Recurring [Member] | Not for Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities		4,715	2,244
Fair Value, Measurements, Recurring [Member] | Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		19,004	28,453
Fair Value, Measurements, Recurring [Member] | Not for Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		1,883	2,094
Fair Value, Measurements, Recurring [Member] | Fixed Income Mutual Fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities		177	161
Fair Value, Measurements, Recurring [Member] | Financial Services Industry [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities		995	864
Fair Value, Measurements, Recurring [Member] | US Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		95,526
Fair Value, Measurements, Recurring [Member] | U.S. Government-Sponsored Entities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		306,934	343,942
Fair Value, Measurements, Recurring [Member] | Agency Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		1,577,596	1,598,874
Fair Value, Measurements, Recurring [Member] | Agency Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		831,817	794,957
Fair Value, Measurements, Recurring [Member] | Non-Agency Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		0	1
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		168,324
Fair Value, Measurements, Recurring [Member] | States of the U.S. and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		20,735	21,093
Fair Value, Measurements, Recurring [Member] | Other Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		1,855	4,670
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		0	0
Equity securities		177	161
Assets measured at fair value, securities available for sale			161
Loans held for sale		0	0
Derivative assets		0	0
Assets measured at fair value on a recurring basis, Total		177	161
Derivative liabilities		0	0
Liabilities measured at fair value on a recurring basis, Total		0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities		0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Not for Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities		0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Not for Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Fixed Income Mutual Fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities		177	161
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Financial Services Industry [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities		0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | US Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | U.S. Government-Sponsored Entities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Agency Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Agency Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Non-Agency Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | States of the U.S. and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Other Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		0	0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		3,002,787	2,763,537
Equity securities		995	864
Assets measured at fair value, securities available for sale			2,764,401
Loans held for sale		28,213	56,458
Derivative assets		19,225	28,953
Assets measured at fair value on a recurring basis, Total		3,051,220	2,849,812
Derivative liabilities		66,436	29,192
Liabilities measured at fair value on a recurring basis, Total		66,436	29,192
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities		61,728	26,953
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Not for Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities		4,708	2,239
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		19,004	28,453
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Not for Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		221	500
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Fixed Income Mutual Fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities		0	0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Financial Services Industry [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities		995	864
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | US Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		95,526
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | U.S. Government-Sponsored Entities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		306,934	343,942
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Agency Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		1,577,596	1,598,874
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Agency Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		831,817	794,957
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Non-Agency Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		0	1
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		168,324
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | States of the U.S. and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		20,735	21,093
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Other Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		1,855	4,670
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		0	0
Equity securities		0	0
Assets measured at fair value, securities available for sale			0
Loans held for sale		0	0
Derivative assets		1,662	1,594
Assets measured at fair value on a recurring basis, Total		1,662	1,594
Derivative liabilities		7	5
Liabilities measured at fair value on a recurring basis, Total		7	5
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities		0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Not for Trading Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities		7	5
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Not for Trading Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		1,662	1,594
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Fixed Income Mutual Fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities		0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Financial Services Industry [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities		0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | US Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | U.S. Government-Sponsored Entities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Agency Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Agency Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Non-Agency Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | States of the U.S. and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Other Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities		$ 0	$ 0

[1] Amount represents loans for which we have elected the fair value option. See Note 18.