BUSINESS SEGMENTS - Financial Information for Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Interest income	$ 294,117	$ 251,034	$ 567,044	$ 445,727
Interest expense	54,762	32,619	101,584	54,560
Net Interest Income	239,355	218,415	465,460	391,167
Provision for credit losses	15,554	16,756	30,049	27,606
Non-interest income	64,889	66,078	132,392	121,194
Non-interest expense	179,202	158,901	346,067	343,358
Amortization of intangibles	3,811	4,813	8,029	7,911
Income tax expense (benefit)	20,471	29,617	41,739	36,101
Net income (loss)	85,206	74,406	171,968	97,385
Total assets	32,257,563	30,753,726	32,257,563	30,753,726	$ 31,417,635
Total intangibles	2,335,445	2,346,654	2,335,445	2,346,654
Operating Segments [Member] | Community Banking [Member]
Segment Reporting Information [Line Items]
Interest income	284,768	241,917	548,355	427,298
Interest expense	50,118	28,414	92,478	47,279
Net Interest Income	234,650	213,503	455,877	380,019
Provision for credit losses	13,277	14,738	25,689	23,802
Non-interest income	51,137	53,031	104,449	93,748
Non-interest expense	159,675	141,441	308,342	309,725
Amortization of intangibles	3,699	4,694	7,804	7,676
Income tax expense (benefit)	21,291	30,200	43,011	36,511
Net income (loss)	87,845	75,461	175,480	96,053
Total assets	32,034,457	30,487,402	32,034,457	30,487,402
Total intangibles	2,311,429	2,322,326	2,311,429	2,322,326
Operating Segments [Member] | Wealth Management [Member]
Segment Reporting Information [Line Items]
Interest income	0	0	0	0
Interest expense	0	0	0	0
Net Interest Income	0	0	0	0
Provision for credit losses	0	0	0	0
Non-interest income	11,239	9,821	22,241	19,370
Non-interest expense	8,694	7,987	16,972	15,527
Amortization of intangibles	60	65	121	126
Income tax expense (benefit)	581	651	1,170	1,362
Net income (loss)	1,904	1,118	3,978	2,355
Total assets	25,152	22,028	25,152	22,028
Total intangibles	10,067	10,288	10,067	10,288
Operating Segments [Member] | Insurance [Member]
Segment Reporting Information [Line Items]
Interest income	19	19	39	39
Interest expense	0	0	0	0
Net Interest Income	19	19	39	39
Provision for credit losses	0	0	0	0
Non-interest income	3,695	3,496	7,998	7,821
Non-interest expense	3,895	3,456	7,606	6,771
Amortization of intangibles	52	54	104	109
Income tax expense (benefit)	(43)	10	81	357
Net income (loss)	(190)	(5)	246	623
Total assets	22,114	22,311	22,114	22,311
Total intangibles	12,140	12,231	12,140	12,231
Operating Segments [Member] | Consumer Finance [Member]
Segment Reporting Information [Line Items]
Interest income	9,349	10,114	18,643	20,016
Interest expense	885	888	1,795	1,810
Net Interest Income	8,464	9,226	16,848	18,206
Provision for credit losses	2,277	2,018	4,360	3,804
Non-interest income	653	770	1,291	1,480
Non-interest expense	5,293	5,288	10,523	10,519
Amortization of intangibles	0	0	0	0
Income tax expense (benefit)	444	1,073	918	2,140
Net income (loss)	1,103	1,617	2,338	3,223
Total assets	167,678	183,859	167,678	183,859
Total intangibles	1,809	1,809	1,809	1,809
Parent and Other [Member]
Segment Reporting Information [Line Items]
Interest income	(19)	(1,016)	7	(1,626)
Interest expense	3,759	3,317	7,311	5,471
Net Interest Income	(3,778)	(4,333)	(7,304)	(7,097)
Provision for credit losses	0	0	0	0
Non-interest income	(1,835)	(1,040)	(3,587)	(1,225)
Non-interest expense	1,645	729	2,624	816
Amortization of intangibles	0	0	0	0
Income tax expense (benefit)	(1,802)	(2,317)	(3,441)	(4,269)
Net income (loss)	(5,456)	(3,785)	(10,074)	(4,869)
Total assets	8,162	38,126	8,162	38,126
Total intangibles	$ 0	$ 0	$ 0	$ 0