SECURITIES - Amortized Cost and Fair Value of Securities Available for Sale (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Debt Securities
Amortized Cost	$ 3,402,446
Gross Unrealized Gains	392
Gross Unrealized Losses	(103,944)
Fair Value	3,298,894
Equity Securities
Amortized Cost		$ 2,802,621
Gross Unrealized Gains		1,721
Gross Unrealized Losses		(39,780)
Securities available for sale	3,298,894	2,764,562
US Government Agencies [Member]
Debt Securities
Amortized Cost	163,752
Gross Unrealized Gains	36
Gross Unrealized Losses	(788)
Fair Value	163,000
U.S. Government-Sponsored Entities [Member]
Debt Securities
Amortized Cost	362,967	347,767
Gross Unrealized Gains	0	52
Gross Unrealized Losses	(6,700)	(3,877)
Fair Value	356,267	343,942
Agency Mortgage-Backed Securities [Member]
Debt Securities
Amortized Cost	1,540,049	1,615,168
Gross Unrealized Gains	356	1,225
Gross Unrealized Losses	(56,585)	(17,519)
Fair Value	1,483,820	1,598,874
Agency Collateralized Mortgage Obligations [Member]
Debt Securities
Amortized Cost	1,083,989	813,034
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(37,508)	(18,077)
Fair Value	1,046,481	794,957
Non-Agency Collateralized Mortgage Obligations [Member]
Debt Securities
Amortized Cost		1
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Fair Value		1
Commercial Mortgage-Backed Securities [Member]
Debt Securities
Amortized Cost	228,957
Gross Unrealized Gains	0
Gross Unrealized Losses	(2,182)
Fair Value	226,775
States of the U.S. and Political Subdivisions [Member]
Debt Securities
Amortized Cost	20,782	21,151
Gross Unrealized Gains	0	6
Gross Unrealized Losses	(101)	(64)
Fair Value	20,681	21,093
Other Debt Securities [Member]
Debt Securities
Amortized Cost	1,950	4,913
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(80)	(243)
Fair Value	$ 1,870	4,670
Debt Securities [Member]
Debt Securities
Amortized Cost		2,802,034
Gross Unrealized Gains		1,283
Gross Unrealized Losses		(39,780)
Fair Value		2,763,537
Equity Securities [Member]
Equity Securities
Amortized Cost		587
Gross Unrealized Gains		438
Gross Unrealized Losses		0
Fair Value		$ 1,025

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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