SECURITIES - Amortized Cost and Fair Value of Securities Available for Sale (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 2,611,409	$ 2,260,021
Gross Unrealized Gains	4,508	4,172
Gross Unrealized Losses	(22,462)	(32,206)
Fair Value	2,593,455	2,231,987
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	29,942	29,874
Gross Unrealized Gains	7	79
Gross Unrealized Losses	0	0
Fair Value	29,949	29,953
U.S. Government-Sponsored Entities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	382,668	367,604
Gross Unrealized Gains	518	864
Gross Unrealized Losses	(2,853)	(3,370)
Fair Value	380,333	365,098
Agency Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,672,304	1,267,535
Gross Unrealized Gains	3,116	2,257
Gross Unrealized Losses	(9,913)	(16,994)
Fair Value	1,665,507	1,252,798
Agency Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	483,556	546,659
Gross Unrealized Gains	284	419
Gross Unrealized Losses	(9,373)	(11,104)
Fair Value	474,467	535,974
Non-Agency Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2	891
Gross Unrealized Gains	0	6
Gross Unrealized Losses	0	0
Fair Value	2	897
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	315	1,292
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	(1)
Fair Value	315	1,291
States of the U.S. and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	31,048	36,065
Gross Unrealized Gains	49	86
Gross Unrealized Losses	(27)	(302)
Fair Value	31,070	35,849
Other Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9,878	9,828
Gross Unrealized Gains	39	94
Gross Unrealized Losses	(229)	(435)
Fair Value	9,688	9,487
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,609,713	2,259,748
Gross Unrealized Gains	4,013	3,805
Gross Unrealized Losses	(22,395)	(32,206)
Fair Value	2,591,331	2,231,347
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,696	273
Gross Unrealized Gains	495	367
Gross Unrealized Losses	(67)	0
Fair Value	$ 2,124	$ 640

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66010992&loc=d3e26610-111562

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
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