LOANS AND LEASES AND ALLOWANCE FOR LOAN AND LEASE LOSSES - Allowance for Loan and Lease Losses and Recorded Investment Excluding Accrued Interest in Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	$ 29,480	$ 18,805	$ 18,805
Charge-offs	(357)	(203)
Recoveries	222	435
Transfer of loans from (to) held-for-sale	0	(963)	(963)
Provision	0	1,929
Balance at end of period	29,345	20,003	29,480
Individually evaluated for impairment	1,199	62
Collectively evaluated for impairment	27,940	19,745
Acquired with deteriorated credit quality	206	196
Loans:
Individually evaluated for impairment	32,119	15,264
Collectively evaluated for impairment	3,659,798	2,068,308
Acquired with deteriorated credit quality	241,798	313,423
Total ending loan balances	3,933,715	2,396,995	3,949,122
Commercial and industrial
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	6,910	1,822	1,822
Charge-offs	(11)	0
Recoveries	3	26
Transfer of loans from (to) held-for-sale			0
Provision	(418)	519
Balance at end of period	6,484	2,367	6,910
Individually evaluated for impairment	749	0
Collectively evaluated for impairment	5,677	2,367
Acquired with deteriorated credit quality	58	0
Loans:
Individually evaluated for impairment	8,087	0
Collectively evaluated for impairment	480,063	297,646
Acquired with deteriorated credit quality	1,079	1,538
Total ending loan balances	489,229	299,184	490,900
Commercial real estate
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	3,840	5,484	5,484
Charge-offs	(259)	0
Recoveries	132	316
Transfer of loans from (to) held-for-sale			0
Provision	191	649
Balance at end of period	3,904	6,449	3,840
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	3,792	6,449
Acquired with deteriorated credit quality	112	0
Loans:
Individually evaluated for impairment	373	3,218
Collectively evaluated for impairment	964,929	542,750
Acquired with deteriorated credit quality	10,432	14,613
Total ending loan balances	975,734	560,581	999,857
Multi-family
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	7,179	2,566	2,566
Charge-offs	0	0
Recoveries	3	0
Transfer of loans from (to) held-for-sale			0
Provision	(18)	154
Balance at end of period	7,164	2,720	7,179
Individually evaluated for impairment	0	37
Collectively evaluated for impairment	7,164	2,683
Acquired with deteriorated credit quality	0	0
Loans:
Individually evaluated for impairment	1,566	1,674
Collectively evaluated for impairment	938,487	153,708
Acquired with deteriorated credit quality	0	0
Total ending loan balances	940,053	155,382	955,683
SBA
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	335	235	235
Charge-offs	0	(17)
Recoveries	72	92
Transfer of loans from (to) held-for-sale			0
Provision	159	(99)
Balance at end of period	566	211	335
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	547	211
Acquired with deteriorated credit quality	19	0
Loans:
Individually evaluated for impairment	9	0
Collectively evaluated for impairment	45,109	23,064
Acquired with deteriorated credit quality	3,136	3,477
Total ending loan balances	48,254	26,541	36,155
Construction
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	846	244	244
Charge-offs	0	0
Recoveries	0	0
Transfer of loans from (to) held-for-sale			0
Provision	(151)	108
Balance at end of period	695	352	846
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	695	352
Acquired with deteriorated credit quality	0	0
Loans:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	38,081	25,144
Acquired with deteriorated credit quality	0	0
Total ending loan balances	38,081	25,144	42,198
Lease financing
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	873	428	428
Charge-offs	(87)	0
Recoveries	0	0
Transfer of loans from (to) held-for-sale			0
Provision	409	194
Balance at end of period	1,195	622	873
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	1,195	622
Acquired with deteriorated credit quality	0	0
Loans:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	102,012	48,537
Acquired with deteriorated credit quality	0	0
Total ending loan balances	102,012	48,537	85,749
Single Family Residential Mortgage
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	7,192	7,044	7,044
Charge-offs	0	(151)
Recoveries	0	0
Transfer of loans from (to) held-for-sale			(963)
Provision	(232)	217
Balance at end of period	6,960	6,147	7,192
Individually evaluated for impairment	450	25
Collectively evaluated for impairment	6,493	5,926
Acquired with deteriorated credit quality	17	196
Loans:
Individually evaluated for impairment	21,790	10,160
Collectively evaluated for impairment	920,193	856,664
Acquired with deteriorated credit quality	227,151	292,039
Total ending loan balances	1,169,134	1,158,863
Other Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	2,305	532	532
Charge-offs	0	(35)
Recoveries	12	1
Transfer of loans from (to) held-for-sale			0
Provision	(304)	284
Balance at end of period	2,013	782	2,305
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	2,013	782
Acquired with deteriorated credit quality	0	0
Loans:
Individually evaluated for impairment	294	212
Collectively evaluated for impairment	170,924	120,795
Acquired with deteriorated credit quality	0	1,756
Total ending loan balances	171,218	122,763
Unallocated
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	0	450	450
Charge-offs	0	0
Recoveries	0	0
Transfer of loans from (to) held-for-sale			0
Provision	364	(97)
Balance at end of period	364	353	0
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	364	353
Acquired with deteriorated credit quality	0	0
Loans:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	0	0
Acquired with deteriorated credit quality	0	0
Total ending loan balances	$ 0	$ 0

LOANS AND LEASES AND ALLOWANCE FOR LOAN AND LEASE LOSSES - Allowance for Loan and Lease Losses and Recorded Investment Excluding Accrued Interest in Loans (Detail) (USD $)
In Thousands, unless otherwise specified