SECURITIES - Fair Values and Unrealized Losses of Impaired Securities, by Length of Impairment (Detail) $ in Thousands	Jun. 30, 2017 USD ($) Security	Dec. 31, 2016 USD ($) Security
Schedule Of Securities [Line Items]
Number of available for sale securities, Less than 1 year | Security	119	113
Number of available for sale securities, Greater than 1 year | Security	16	12
Number of available for sale securities | Security	135	125
Securities Available For Sale, Less than 12 Months, Fair Value	$ 1,741,671	$ 1,644,951
Securities Available For Sale, Less than 12 Months, Unrealized Losses	(18,716)	(27,928)
Securities Available For Sale, 12 Months or More, Fair Value	99,206	93,510
Securities Available For Sale, 12 Months or More, Unrealized Losses	(3,746)	(4,278)
Securities Available For Sale, Fair Value, Total	1,840,877	1,738,461
Securities Available For Sale, Unrealized Losses, Total	$ (22,462)	$ (32,206)
Number of held to maturity securities | Security	150	186
Securities Held To Maturity, Less than 12 Months, Fair Value	$ 1,531,699	$ 1,513,912
Securities Held To Maturity, Less than 12 Months, Unrealized Losses	(32,672)	(46,484)
Securities Held To Maturity, Greater than 12 Months, Fair Value	99,316	120,957
Securities Held To Maturity, Greater than 12 Months, Unrealized Losses	(2,842)	(4,307)
Securities Held To Maturity, Fair Value, Total	1,631,015	1,634,869
Securities Held To Maturity, Unrealized Losses, Total	$ (35,514)	$ (50,791)
Less than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities | Security	138	173
Greater than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities | Security	12	13
U.S. Government-Sponsored Entities [Member]
Schedule Of Securities [Line Items]
Number of available for sale securities, Less than 1 year | Security	13	11
Number of available for sale securities, Greater than 1 year | Security	0	0
Number of available for sale securities | Security	13	11
Securities Available For Sale, Less than 12 Months, Fair Value	$ 237,159	$ 211,636
Securities Available For Sale, Less than 12 Months, Unrealized Losses	(2,853)	(3,370)
Securities Available For Sale, 12 Months or More, Fair Value	0	0
Securities Available For Sale, 12 Months or More, Unrealized Losses	0	0
Securities Available For Sale, Fair Value, Total	237,159	211,636
Securities Available For Sale, Unrealized Losses, Total	$ (2,853)	$ (3,370)
Number of held to maturity securities | Security	11	10
Securities Held To Maturity, Less than 12 Months, Fair Value	$ 201,295	$ 185,525
Securities Held To Maturity, Less than 12 Months, Unrealized Losses	(3,704)	(4,475)
Securities Held To Maturity, Greater than 12 Months, Fair Value	0	0
Securities Held To Maturity, Greater than 12 Months, Unrealized Losses	0	0
Securities Held To Maturity, Fair Value, Total	201,295	185,525
Securities Held To Maturity, Unrealized Losses, Total	$ (3,704)	$ (4,475)
U.S. Government-Sponsored Entities [Member] | Less than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities | Security	11	10
U.S. Government-Sponsored Entities [Member] | Greater than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities | Security	0	0
Agency Mortgage-Backed Securities [Member]
Schedule Of Securities [Line Items]
Number of available for sale securities, Less than 1 year | Security	57	55
Number of available for sale securities, Greater than 1 year | Security	0	0
Number of available for sale securities | Security	57	55
Securities Available For Sale, Less than 12 Months, Fair Value	$ 1,185,412	$ 1,056,731
Securities Available For Sale, Less than 12 Months, Unrealized Losses	(9,913)	(16,994)
Securities Available For Sale, 12 Months or More, Fair Value	0	0
Securities Available For Sale, 12 Months or More, Unrealized Losses	0	0
Securities Available For Sale, Fair Value, Total	1,185,412	1,056,731
Securities Available For Sale, Unrealized Losses, Total	$ (9,913)	$ (16,994)
Number of held to maturity securities | Security	37	36
Securities Held To Maturity, Less than 12 Months, Fair Value	$ 668,448	$ 551,404
Securities Held To Maturity, Less than 12 Months, Unrealized Losses	(5,561)	(8,645)
Securities Held To Maturity, Greater than 12 Months, Fair Value	0	0
Securities Held To Maturity, Greater than 12 Months, Unrealized Losses	0	0
Securities Held To Maturity, Fair Value, Total	668,448	551,404
Securities Held To Maturity, Unrealized Losses, Total	$ (5,561)	$ (8,645)
Agency Mortgage-Backed Securities [Member] | Less than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities | Security	37	36
Agency Mortgage-Backed Securities [Member] | Greater than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities | Security	0	0
Agency Collateralized Mortgage Obligations [Member]
Schedule Of Securities [Line Items]
Number of available for sale securities, Less than 1 year | Security	35	26
Number of available for sale securities, Greater than 1 year | Security	10	9
Number of available for sale securities | Security	45	35
Securities Available For Sale, Less than 12 Months, Fair Value	$ 302,658	$ 346,662
Securities Available For Sale, Less than 12 Months, Unrealized Losses	(5,864)	(7,261)
Securities Available For Sale, 12 Months or More, Fair Value	90,687	89,040
Securities Available For Sale, 12 Months or More, Unrealized Losses	(3,509)	(3,843)
Securities Available For Sale, Fair Value, Total	393,345	435,702
Securities Available For Sale, Unrealized Losses, Total	$ (9,373)	$ (11,104)
Number of held to maturity securities | Security	40	41
Securities Held To Maturity, Less than 12 Months, Fair Value	$ 470,354	$ 516,237
Securities Held To Maturity, Less than 12 Months, Unrealized Losses	(11,451)	(13,710)
Securities Held To Maturity, Greater than 12 Months, Fair Value	91,676	112,690
Securities Held To Maturity, Greater than 12 Months, Unrealized Losses	(2,615)	(4,091)
Securities Held To Maturity, Fair Value, Total	562,030	628,927
Securities Held To Maturity, Unrealized Losses, Total	$ (14,066)	$ (17,801)
Agency Collateralized Mortgage Obligations [Member] | Less than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities | Security	29	29
Agency Collateralized Mortgage Obligations [Member] | Greater than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities | Security	11	12
Non-Agency Collateralized Mortgage Obligations [Member]
Schedule Of Securities [Line Items]
Number of available for sale securities, Less than 1 year | Security	1
Number of available for sale securities, Greater than 1 year | Security	0
Number of available for sale securities | Security	1
Securities Available For Sale, Less than 12 Months, Fair Value	$ 2
Securities Available For Sale, Less than 12 Months, Unrealized Losses	0
Securities Available For Sale, 12 Months or More, Fair Value	0
Securities Available For Sale, 12 Months or More, Unrealized Losses	0
Securities Available For Sale, Fair Value, Total	2
Securities Available For Sale, Unrealized Losses, Total	$ 0
Number of held to maturity securities | Security		3
Securities Held To Maturity, Less than 12 Months, Fair Value		$ 1,128
Securities Held To Maturity, Less than 12 Months, Unrealized Losses		(6)
Securities Held To Maturity, Greater than 12 Months, Fair Value		0
Securities Held To Maturity, Greater than 12 Months, Unrealized Losses		0
Securities Held To Maturity, Fair Value, Total		1,128
Securities Held To Maturity, Unrealized Losses, Total		$ (6)
Non-Agency Collateralized Mortgage Obligations [Member] | Less than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities | Security		3
Non-Agency Collateralized Mortgage Obligations [Member] | Greater than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities | Security		0
Commercial Mortgage-Backed Securities [Member]
Schedule Of Securities [Line Items]
Number of available for sale securities, Less than 1 year | Security	1	1
Number of available for sale securities, Greater than 1 year | Security	0	0
Number of available for sale securities | Security	1	1
Securities Available For Sale, Less than 12 Months, Fair Value	$ 315	$ 1,291
Securities Available For Sale, Less than 12 Months, Unrealized Losses	0	(1)
Securities Available For Sale, 12 Months or More, Fair Value	0	0
Securities Available For Sale, 12 Months or More, Unrealized Losses	0	0
Securities Available For Sale, Fair Value, Total	315	1,291
Securities Available For Sale, Unrealized Losses, Total	$ 0	$ (1)
Number of held to maturity securities | Security	4	2
Securities Held To Maturity, Less than 12 Months, Fair Value	$ 14,839	$ 12,317
Securities Held To Maturity, Less than 12 Months, Unrealized Losses	(52)	(10)
Securities Held To Maturity, Greater than 12 Months, Fair Value	7,640	8,267
Securities Held To Maturity, Greater than 12 Months, Unrealized Losses	(227)	(216)
Securities Held To Maturity, Fair Value, Total	22,479	20,584
Securities Held To Maturity, Unrealized Losses, Total	$ (279)	$ (226)
Commercial Mortgage-Backed Securities [Member] | Less than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities | Security	3	1
Commercial Mortgage-Backed Securities [Member] | Greater than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities | Security	1	1
States of the U.S. and Political Subdivisions [Member]
Schedule Of Securities [Line Items]
Number of available for sale securities, Less than 1 year | Security	9	20
Number of available for sale securities, Greater than 1 year | Security	3	0
Number of available for sale securities | Security	12	20
Securities Available For Sale, Less than 12 Months, Fair Value	$ 14,906	$ 28,631
Securities Available For Sale, Less than 12 Months, Unrealized Losses	(19)	(302)
Securities Available For Sale, 12 Months or More, Fair Value	3,839	0
Securities Available For Sale, 12 Months or More, Unrealized Losses	(8)	0
Securities Available For Sale, Fair Value, Total	18,745	28,631
Securities Available For Sale, Unrealized Losses, Total	$ (27)	$ (302)
Number of held to maturity securities | Security	58	94
Securities Held To Maturity, Less than 12 Months, Fair Value	$ 176,763	$ 247,301
Securities Held To Maturity, Less than 12 Months, Unrealized Losses	(11,904)	(19,638)
Securities Held To Maturity, Greater than 12 Months, Fair Value	0	0
Securities Held To Maturity, Greater than 12 Months, Unrealized Losses	0	0
Securities Held To Maturity, Fair Value, Total	176,763	247,301
Securities Held To Maturity, Unrealized Losses, Total	$ (11,904)	$ (19,638)
States of the U.S. and Political Subdivisions [Member] | Less than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities | Security	58	94
States of the U.S. and Political Subdivisions [Member] | Greater than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities | Security	0	0
Other Debt Securities [Member]
Schedule Of Securities [Line Items]
Number of available for sale securities, Less than 1 year | Security	0	0
Number of available for sale securities, Greater than 1 year | Security	3	3
Number of available for sale securities | Security	3	3
Securities Available For Sale, Less than 12 Months, Fair Value	$ 0	$ 0
Securities Available For Sale, Less than 12 Months, Unrealized Losses	0	0
Securities Available For Sale, 12 Months or More, Fair Value	4,680	4,470
Securities Available For Sale, 12 Months or More, Unrealized Losses	(229)	(435)
Securities Available For Sale, Fair Value, Total	4,680	4,470
Securities Available For Sale, Unrealized Losses, Total	$ (229)	$ (435)
Equity Securities [Member]
Schedule Of Securities [Line Items]
Number of available for sale securities, Less than 1 year | Security	3
Number of available for sale securities, Greater than 1 year | Security	0
Number of available for sale securities | Security	3
Securities Available For Sale, Less than 12 Months, Fair Value	$ 1,219
Securities Available For Sale, Less than 12 Months, Unrealized Losses	(67)
Securities Available For Sale, 12 Months or More, Fair Value	0
Securities Available For Sale, 12 Months or More, Unrealized Losses	0
Securities Available For Sale, Fair Value, Total	1,219
Securities Available For Sale, Unrealized Losses, Total	$ (67)