BUSINESS SEGMENTS - Financial Information for Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Interest income	$ 251,034	$ 170,931	$ 445,727	$ 326,685
Interest expense	32,619	16,562	54,560	31,962
Net Interest Income	218,415	154,369	391,167	294,723
Provision for credit losses	16,756	16,640	27,606	28,408
Non-interest income	66,078	51,411	121,194	97,455
Non-interest expense	158,901	126,241	343,358	260,240
Amortization of intangibles	4,813	3,388	7,911	6,037
Income tax expense (benefit)	29,617	18,211	36,101	30,061
Net income (loss)	74,406	41,300	97,385	67,432
Total assets	30,753,726	21,214,967	30,753,726	21,214,967	$ 21,844,817
Total intangibles	2,376,382	1,104,991	2,376,382	1,104,991
Operating Segments [Member] | Community Banking [Member]
Segment Reporting Information [Line Items]
Interest income	241,917	161,691	427,298	308,275
Interest expense	28,414	13,767	47,279	26,362
Net Interest Income	213,503	147,924	380,019	281,913
Provision for credit losses	14,738	15,168	23,802	25,410
Non-interest income	53,031	39,137	93,748	69,923
Non-interest expense	141,441	110,201	309,725	228,536
Amortization of intangibles	4,694	3,180	7,676	5,621
Income tax expense (benefit)	30,200	17,665	36,511	28,282
Net income (loss)	75,461	40,847	96,053	63,987
Total assets	30,487,402	20,989,188	30,487,402	20,989,188
Total intangibles	2,352,054	1,080,385	2,352,054	1,080,385
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	9,821	9,183	19,370	17,999
Non-interest expense	7,987	6,960	15,527	14,049
Amortization of intangibles	65	64	126	129
Income tax expense (benefit)	651	782	1,362	1,387
Net income (loss)	1,118	1,377	2,355	2,434
Total assets	22,028	20,044	22,028	20,044
Total intangibles	10,288	10,318	10,288	10,318
Operating Segments [Member] | Insurance [Member]
Segment Reporting Information [Line Items]
Interest income	19	21	39	43
Interest expense	0	0	0	0
Net Interest Income	19	21	39	43
Provision for credit losses	0	0	0	0
Non-interest income	3,496	3,268	7,821	7,462
Non-interest expense	3,456	3,276	6,771	6,577
Amortization of intangibles	54	144	109	287
Income tax expense (benefit)	10	(41)	357	234
Net income (loss)	(5)	(90)	623	407
Total assets	22,311	22,732	22,311	22,732
Total intangibles	12,231	12,479	12,231	12,479
Operating Segments [Member] | Consumer Finance [Member]
Segment Reporting Information [Line Items]
Interest income	10,114	10,126	20,016	19,911
Interest expense	888	930	1,810	1,871
Net Interest Income	9,226	9,196	18,206	18,040
Provision for credit losses	2,018	1,472	3,804	2,998
Non-interest income	770	754	1,480	1,470
Non-interest expense	5,288	5,372	10,519	10,576
Amortization of intangibles	0	0	0	0
Income tax expense (benefit)	1,073	1,208	2,140	2,320
Net income (loss)	1,617	1,898	3,223	3,616
Total assets	183,859	196,603	183,859	196,603
Total intangibles	1,809	1,809	1,809	1,809
Parent and Other [Member]
Segment Reporting Information [Line Items]
Interest income	(1,016)	(907)	(1,626)	(1,544)
Interest expense	3,317	1,865	5,471	3,729
Net Interest Income	(4,333)	(2,772)	(7,097)	(5,273)
Provision for credit losses	0	0	0	0
Non-interest income	(1,040)	(931)	(1,225)	601
Non-interest expense	729	432	816	502
Amortization of intangibles	0	0	0	0
Income tax expense (benefit)	(2,317)	(1,403)	(4,269)	(2,162)
Net income (loss)	(3,785)	(2,732)	(4,869)	(3,012)
Total assets	38,126	(13,600)	38,126	(13,600)
Total intangibles	$ 0	$ 0	$ 0	$ 0