Loans Held for Investment, net - Impaired Loans Segregated by Loans with No Specific Allowance and Loans with Allowance by Class of Loans (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Impaired [Line Items]
With no specific allowance recorded, Recorded Investment		$ 20,757	$ 54,513
With no specific allowance recorded, Unpaid Principal Balance		23,631	77,820
With no specific allowance recorded, Average Carrying Amount		40,831	60,230
With no specific allowance recorded, Year-to-Date Interest Income Recognized		1,051	2,089
With an allowance recorded, Recorded Investment		23,145	40,772
With an allowance recorded, Unpaid Principal Balance		27,461	45,427
With an allowance recorded, Average Carrying Amount		26,149	33,268
With an allowance recorded, Year-to-Date Interest Income Recognized		938	1,490
Recorded Investment, Total		43,902	95,285
Unpaid Principal Balance, Total		51,092	123,247
Associated Allowance, Total	$ 24,491	4,307	8,441
Average Carrying Amount, Total		66,980	93,498
Year to Date Interest Income Recognized, Total	2,097	1,989	3,579
Education
Financing Receivable, Impaired [Line Items]
With no specific allowance recorded, Recorded Investment		0	205
With no specific allowance recorded, Unpaid Principal Balance		0	205
With no specific allowance recorded, Average Carrying Amount		0	101
With no specific allowance recorded, Year-to-Date Interest Income Recognized		0	0
With an allowance recorded, Recorded Investment		191	0
With an allowance recorded, Unpaid Principal Balance		191	0
With an allowance recorded, Average Carrying Amount		104	0
With an allowance recorded, Year-to-Date Interest Income Recognized		0	0
Recorded Investment, Total		191	205
Unpaid Principal Balance, Total		191	205
Associated Allowance, Total		191	0
Average Carrying Amount, Total		104	101
Year to Date Interest Income Recognized, Total	0	0	0
Land and construction
Financing Receivable, Impaired [Line Items]
With no specific allowance recorded, Recorded Investment			9,421
With no specific allowance recorded, Unpaid Principal Balance			19,334
With no specific allowance recorded, Average Carrying Amount			12,192
With no specific allowance recorded, Year-to-Date Interest Income Recognized			208
With an allowance recorded, Recorded Investment			8,362
With an allowance recorded, Unpaid Principal Balance			12,536
With an allowance recorded, Average Carrying Amount			4,440
With an allowance recorded, Year-to-Date Interest Income Recognized			180
Recorded Investment, Total			17,783
Unpaid Principal Balance, Total			31,870
Associated Allowance, Total			3,657
Average Carrying Amount, Total			16,632
Year to Date Interest Income Recognized, Total	142	217	388
Multi-family
Financing Receivable, Impaired [Line Items]
With no specific allowance recorded, Recorded Investment			17,614
With no specific allowance recorded, Unpaid Principal Balance			19,863
With no specific allowance recorded, Average Carrying Amount			17,979
With no specific allowance recorded, Year-to-Date Interest Income Recognized			780
With an allowance recorded, Recorded Investment			11,641
With an allowance recorded, Unpaid Principal Balance			11,641
With an allowance recorded, Average Carrying Amount			10,465
With an allowance recorded, Year-to-Date Interest Income Recognized			485
Recorded Investment, Total			29,255
Unpaid Principal Balance, Total			31,504
Associated Allowance, Total			1,308
Average Carrying Amount, Total			28,444
Year to Date Interest Income Recognized, Total	233	961	1,265
Retail/office
Financing Receivable, Impaired [Line Items]
With no specific allowance recorded, Recorded Investment			7,840
With no specific allowance recorded, Unpaid Principal Balance			15,581
With no specific allowance recorded, Average Carrying Amount			8,040
With no specific allowance recorded, Year-to-Date Interest Income Recognized			354
With an allowance recorded, Recorded Investment			9,387
With an allowance recorded, Unpaid Principal Balance			9,566
With an allowance recorded, Average Carrying Amount			8,207
With an allowance recorded, Year-to-Date Interest Income Recognized			356
Recorded Investment, Total			17,227
Unpaid Principal Balance, Total			25,147
Associated Allowance, Total			1,391
Average Carrying Amount, Total			16,247
Year to Date Interest Income Recognized, Total	604	104	710
Residential
Financing Receivable, Impaired [Line Items]
With no specific allowance recorded, Recorded Investment		4,143	4,992
With no specific allowance recorded, Unpaid Principal Balance		5,193	6,406
With no specific allowance recorded, Average Carrying Amount		5,303	5,455
With no specific allowance recorded, Year-to-Date Interest Income Recognized		171	165
With an allowance recorded, Recorded Investment		7,516	9,505
With an allowance recorded, Unpaid Principal Balance		7,551	9,671
With an allowance recorded, Average Carrying Amount		6,843	8,574
With an allowance recorded, Year-to-Date Interest Income Recognized		285	403
Recorded Investment, Total		11,659	14,497
Unpaid Principal Balance, Total		12,744	16,077
Associated Allowance, Total	2,424	1,421	1,400
Average Carrying Amount, Total		12,146	14,029
Year to Date Interest Income Recognized, Total	344	456	568
Commercial and industrial
Financing Receivable, Impaired [Line Items]
With no specific allowance recorded, Recorded Investment		65	0
With no specific allowance recorded, Unpaid Principal Balance		88	268
With no specific allowance recorded, Average Carrying Amount		16	843
With no specific allowance recorded, Year-to-Date Interest Income Recognized		3	26
With an allowance recorded, Recorded Investment		119	113
With an allowance recorded, Unpaid Principal Balance		119	236
With an allowance recorded, Average Carrying Amount		63	111
With an allowance recorded, Year-to-Date Interest Income Recognized		0	1
Recorded Investment, Total		184	113
Unpaid Principal Balance, Total		207	504
Associated Allowance, Total	1,745	118	140
Average Carrying Amount, Total		79	954
Year to Date Interest Income Recognized, Total	316	3	27
Commercial real estate
Financing Receivable, Impaired [Line Items]
Associated Allowance, Total	19,845	2,218	6,475
Commercial real estate | Land and construction
Financing Receivable, Impaired [Line Items]
With no specific allowance recorded, Recorded Investment		798
With no specific allowance recorded, Unpaid Principal Balance		1,125
With no specific allowance recorded, Average Carrying Amount		3,515
With no specific allowance recorded, Year-to-Date Interest Income Recognized		36
With an allowance recorded, Recorded Investment		4,795
With an allowance recorded, Unpaid Principal Balance		9,062
With an allowance recorded, Average Carrying Amount		3,917
With an allowance recorded, Year-to-Date Interest Income Recognized		181
Recorded Investment, Total		5,593
Unpaid Principal Balance, Total		10,187
Associated Allowance, Total		980
Average Carrying Amount, Total		7,432
Year to Date Interest Income Recognized, Total		217
Commercial real estate | Multi-family
Financing Receivable, Impaired [Line Items]
With no specific allowance recorded, Recorded Investment		10,932
With no specific allowance recorded, Unpaid Principal Balance		11,300
With no specific allowance recorded, Average Carrying Amount		15,995
With no specific allowance recorded, Year-to-Date Interest Income Recognized		574
With an allowance recorded, Recorded Investment		9,027
With an allowance recorded, Unpaid Principal Balance		9,027
With an allowance recorded, Average Carrying Amount		8,421
With an allowance recorded, Year-to-Date Interest Income Recognized		387
Recorded Investment, Total		19,959
Unpaid Principal Balance, Total		20,327
Associated Allowance, Total		1,166
Average Carrying Amount, Total		24,416
Year to Date Interest Income Recognized, Total		961
Commercial real estate | Retail/office
Financing Receivable, Impaired [Line Items]
With no specific allowance recorded, Recorded Investment		2,235
With no specific allowance recorded, Unpaid Principal Balance		2,593
With no specific allowance recorded, Average Carrying Amount		5,775
With no specific allowance recorded, Year-to-Date Interest Income Recognized		83
With an allowance recorded, Recorded Investment		390
With an allowance recorded, Unpaid Principal Balance		390
With an allowance recorded, Average Carrying Amount		6,073
With an allowance recorded, Year-to-Date Interest Income Recognized		21
Recorded Investment, Total		2,625
Unpaid Principal Balance, Total		2,983
Associated Allowance, Total		50
Average Carrying Amount, Total		11,848
Year to Date Interest Income Recognized, Total		104
Commercial real estate | Other commercial real estate
Financing Receivable, Impaired [Line Items]
With no specific allowance recorded, Recorded Investment		1,479	13,972
With no specific allowance recorded, Unpaid Principal Balance		2,114	15,318
With no specific allowance recorded, Average Carrying Amount		9,046	14,617
With no specific allowance recorded, Year-to-Date Interest Income Recognized		115	467
With an allowance recorded, Recorded Investment		36	923
With an allowance recorded, Unpaid Principal Balance		48	936
With an allowance recorded, Average Carrying Amount		168	854
With an allowance recorded, Year-to-Date Interest Income Recognized		0	17
Recorded Investment, Total		1,515	14,895
Unpaid Principal Balance, Total		2,162	16,254
Associated Allowance, Total		22	119
Average Carrying Amount, Total		9,214	15,471
Year to Date Interest Income Recognized, Total	312	115	484
Consumer loans
Financing Receivable, Impaired [Line Items]
Associated Allowance, Total	477	550	426
Consumer loans | Other consumer
Financing Receivable, Impaired [Line Items]
With no specific allowance recorded, Recorded Investment		1,105	469
With no specific allowance recorded, Unpaid Principal Balance		1,218	845
With no specific allowance recorded, Average Carrying Amount		1,181	1,003
With no specific allowance recorded, Year-to-Date Interest Income Recognized		69	89
With an allowance recorded, Recorded Investment		1,071	841
With an allowance recorded, Unpaid Principal Balance		1,073	841
With an allowance recorded, Average Carrying Amount		560	617
With an allowance recorded, Year-to-Date Interest Income Recognized		64	48
Recorded Investment, Total		2,176	1,310
Unpaid Principal Balance, Total		2,291	1,686
Associated Allowance, Total		359	426
Average Carrying Amount, Total		1,741	1,620
Year to Date Interest Income Recognized, Total	$ 146	$ 133	$ 137