SEGMENT REPORTING - Operating Segments' Financial Results (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net interest income (loss)	$ 86,961	$ 55,550	$ 238,415	$ 161,651
Provision for loan and lease losses	2,592	735	4,682	6,209
Noninterest income	74,630	50,727	192,193	163,400
Noninterest expense	124,262	81,743	313,437	245,542
Income before income taxes	34,737	23,799	112,489	73,300
Total assets	11,216,404	7,256,810	11,216,404	7,256,810	$ 8,235,555
Operating Segments | Commercial Banking
Segment Reporting Information [Line Items]
Net interest income (loss)	85,429	55,911	237,137	162,352
Provision for loan and lease losses	2,592	735	4,682	6,209
Noninterest income	19,536	14,669	63,058	44,013
Noninterest expense	77,177	44,566	181,499	131,708
Income before income taxes	25,196	25,279	114,014	68,448
Total assets	10,606,617	6,822,439	10,606,617	6,822,439
Operating Segments | Mortgage Banking
Segment Reporting Information [Line Items]
Net interest income (loss)	4,108	3,606	10,986	9,593
Provision for loan and lease losses	0	0	0	0
Noninterest income	52,276	33,843	121,115	111,461
Noninterest expense	47,085	35,442	127,130	108,203
Income before income taxes	9,299	2,007	4,971	12,851
Total assets	576,406	418,877	576,406	418,877
Operating Segments | Financial Advisory
Segment Reporting Information [Line Items]
Net interest income (loss)	0	0	0	0
Provision for loan and lease losses	0	0	0	0
Noninterest income	0	3,072	2,636	11,590
Noninterest expense	0	2,592	3,199	9,295
Income before income taxes	0	480	(563)	2,295
Total assets	0	8,670	0	8,670
Operating Segments | Corporate/ Other
Segment Reporting Information [Line Items]
Net interest income (loss)	(2,576)	(3,967)	(9,708)	(10,294)
Provision for loan and lease losses	0	0	0	0
Noninterest income	2,818	0	6,512	0
Noninterest expense	0	0	2,737	0
Income before income taxes	242	(3,967)	(5,933)	(10,294)
Total assets	218,520	175,173	218,520	175,173
Inter-segment Elimination
Segment Reporting Information [Line Items]
Net interest income (loss)	0	0	0	0
Provision for loan and lease losses	0	0	0	0
Noninterest income	0	(857)	(1,128)	(3,664)
Noninterest expense	0	(857)	(1,128)	(3,664)
Income before income taxes	0	0	0	0
Total assets	$ (185,139)	$ (168,349)	$ (185,139)	$ (168,349)