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	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	$ 40,444	$ 35,533
Charge-offs	(357)	(102)
Recoveries	66	93
Provision	2,583	321
Balance at end of period	42,736	35,845
Individually evaluated for impairment			$ 250		$ 1,376
Collectively evaluated for impairment			42,325		34,263
Total ending ALLL balance	40,444	35,533	42,736	$ 40,444	35,845
Loans:
Individually evaluated for impairment			13,395		39,382
Collectively evaluated for impairment			5,952,227		4,739,710
Total ending loan balances			6,105,321	6,034,752	5,463,068
Purchased Credit Impaired
Allowance for Loan and Lease Losses [Roll Forward]
Balance at end of period	161	206
Total ending ALLL balance	161	206	161		206
Loans:
Total ending loan balances			139,699	141,826	683,976
Commercial | Commercial and industrial
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	7,584	5,850
Charge-offs	(250)	0
Recoveries	0	0
Provision	3,554	196
Balance at end of period	10,888	6,046
Individually evaluated for impairment			0		29
Collectively evaluated for impairment			10,888		5,959
Total ending ALLL balance	7,584	5,850	10,888	7,584	6,046
Loans:
Individually evaluated for impairment			0		4,493
Collectively evaluated for impairment			1,580,969		978,649
Total ending loan balances			1,585,656	1,522,960	983,961
Commercial | Commercial and industrial | Purchased Credit Impaired
Allowance for Loan and Lease Losses [Roll Forward]
Balance at end of period	0	58
Total ending ALLL balance	0	58	0		58
Loans:
Total ending loan balances			4,687	4,760	819
Commercial | Commercial real estate
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	5,467	4,252
Charge-offs	0	0
Recoveries	0	0
Provision	(924)	(283)
Balance at end of period	4,543	3,969
Individually evaluated for impairment			0		0
Collectively evaluated for impairment			4,538		3,857
Total ending ALLL balance	5,467	4,252	4,543	5,467	3,969
Loans:
Individually evaluated for impairment			0		299
Collectively evaluated for impairment			749,440		705,176
Total ending loan balances			750,592	729,959	713,693
Commercial | Commercial real estate | Purchased Credit Impaired
Allowance for Loan and Lease Losses [Roll Forward]
Balance at end of period	5	112
Total ending ALLL balance	5	112	5		112
Loans:
Total ending loan balances			1,152	1,182	8,218
Commercial | Multi-family
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	11,376	6,012
Charge-offs	0	0
Recoveries	0	0
Provision	(347)	472
Balance at end of period	11,029	6,484
Individually evaluated for impairment			0		0
Collectively evaluated for impairment			11,029		6,484
Total ending ALLL balance	11,376	6,012	11,029	11,376	6,484
Loans:
Individually evaluated for impairment			0		0
Collectively evaluated for impairment			1,449,715		1,021,097
Total ending loan balances			1,449,715	1,365,262	1,021,097
Commercial | Multi-family | Purchased Credit Impaired
Allowance for Loan and Lease Losses [Roll Forward]
Balance at end of period	0	0
Total ending ALLL balance	0	0	0		0
Loans:
Total ending loan balances			0	0	0
Commercial | SBA
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	939	683
Charge-offs	0	0
Recoveries	43	31
Provision	164	192
Balance at end of period	1,146	906
Individually evaluated for impairment			0		0
Collectively evaluated for impairment			1,127		887
Total ending ALLL balance	939	683	1,146	939	906
Loans:
Individually evaluated for impairment			0		0
Collectively evaluated for impairment			73,433		68,700
Total ending loan balances			76,040	73,840	71,640
Commercial | SBA | Purchased Credit Impaired
Allowance for Loan and Lease Losses [Roll Forward]
Balance at end of period	19	19
Total ending ALLL balance	19	19	19		19
Loans:
Total ending loan balances			2,607	2,672	2,940
Commercial | Construction
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	2,015	1,530
Charge-offs	0	0
Recoveries	0	0
Provision	1,003	(10)
Balance at end of period	3,018	1,520
Individually evaluated for impairment			0		0
Collectively evaluated for impairment			3,018		1,520
Total ending ALLL balance	2,015	1,530	3,018	2,015	1,520
Loans:
Individually evaluated for impairment			1,528		0
Collectively evaluated for impairment			140,636		68,241
Total ending loan balances			142,164	125,100	68,241
Commercial | Construction | Purchased Credit Impaired
Allowance for Loan and Lease Losses [Roll Forward]
Balance at end of period	0	0
Total ending ALLL balance	0	0	0		0
Loans:
Total ending loan balances			0	0	0
Commercial | Lease financing
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	6	2,195
Charge-offs	0	(102)
Recoveries	19	61
Provision	(20)	456
Balance at end of period	5	2,610
Individually evaluated for impairment			0		0
Collectively evaluated for impairment			5		2,610
Total ending ALLL balance	6	2,195	5	6	2,610
Loans:
Individually evaluated for impairment			0		0
Collectively evaluated for impairment			285		212,836
Total ending loan balances			285	379	212,836
Commercial | Lease financing | Purchased Credit Impaired
Allowance for Loan and Lease Losses [Roll Forward]
Balance at end of period	0	0
Total ending ALLL balance	0	0	0		0
Loans:
Total ending loan balances			0	0	0
Consumer | Single Family Residential Mortgage
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	12,075	13,854
Charge-offs	(81)	0
Recoveries	1	0
Provision	(755)	(584)
Balance at end of period	11,240	13,270
Individually evaluated for impairment			250		1,347
Collectively evaluated for impairment			10,853		11,906
Total ending ALLL balance	12,075	13,854	11,240	12,075	13,270
Loans:
Individually evaluated for impairment			10,984		34,296
Collectively evaluated for impairment			1,832,818		1,576,150
Total ending loan balances			1,975,055		2,282,445
Consumer | Single Family Residential Mortgage | Purchased Credit Impaired
Allowance for Loan and Lease Losses [Roll Forward]
Balance at end of period	137	17
Total ending ALLL balance	137	17	137		17
Loans:
Total ending loan balances			131,253		671,999
Consumer | Other Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	982	1,157
Charge-offs	(26)	0
Recoveries	3	1
Provision	(92)	(118)
Balance at end of period	867	1,040
Individually evaluated for impairment			0		0
Collectively evaluated for impairment			867		1,040
Total ending ALLL balance	982	1,157	867	$ 982	1,040
Loans:
Individually evaluated for impairment			883		294
Collectively evaluated for impairment			124,931		108,861
Total ending loan balances			125,814		109,155
Consumer | Other Consumer | Purchased Credit Impaired
Allowance for Loan and Lease Losses [Roll Forward]
Balance at end of period	0	0
Total ending ALLL balance	$ 0	$ 0	0		0
Loans:
Total ending loan balances			$ 0		$ 0