Residential Loans - Loan Product Type and Accompanying Loan Characteristics of Residential Loans (Detail) $ in Thousands	12 Months Ended
Dec. 31, 2015 USD ($) loan	Dec. 31, 2014 USD ($) loan
Residential Loans Held for Investment
Mortgage Loans on Real Estate [Line Items]
Number of loans \| loan	4,545	5,315
Principal value	$ 1,122,415	$ 1,483,213
30-89 Days DQ	30,328	41,248
90+ Days DQ	$ 58,823	$ 69,562
Residential Loans Held for Investment \| ARM Loans
Mortgage Loans on Real Estate [Line Items]
Number of loans \| loan	4,504	5,063
Principal value	$ 1,101,588	$ 1,311,514
30-89 Days DQ	29,786	41,248
90+ Days DQ	58,823	68,517
Residential Loans Held for Investment \| ARM Loans \| Range 1
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum	0	0
Loan Balance, maximum	$ 250	$ 250
Interest Rate, minimum	0.38%	0.25%
Interest Rate, maximum	5.16%	5.50%
Number of loans \| loan	3,133	3,400
Principal value	$ 355,415	$ 400,779
30-89 Days DQ	10,661	14,604
90+ Days DQ	13,078	16,332
Residential Loans Held for Investment \| ARM Loans \| Range 2
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum	251	251
Loan Balance, maximum	$ 500	$ 500
Interest Rate, minimum	0.00%	0.00%
Interest Rate, maximum	5.63%	5.63%
Number of loans \| loan	858	1,041
Principal value	$ 296,425	$ 360,848
30-89 Days DQ	9,620	14,536
90+ Days DQ	15,345	13,955
Residential Loans Held for Investment \| ARM Loans \| Range 3
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum	501	501
Loan Balance, maximum	$ 750	$ 750
Interest Rate, minimum	0.63%	0.50%
Interest Rate, maximum	4.66%	4.66%
Number of loans \| loan	269	328
Principal value	$ 161,273	$ 198,661
30-89 Days DQ	4,578	7,218
90+ Days DQ	7,209	12,862
Residential Loans Held for Investment \| ARM Loans \| Range 4
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum	751	751
Loan Balance, maximum	$ 1,000	$ 1,000
Interest Rate, minimum	0.38%	0.25%
Interest Rate, maximum	2.38%	2.38%
Number of loans \| loan	135	162
Principal value	$ 118,983	$ 143,687
30-89 Days DQ	3,586	2,396
90+ Days DQ	$ 8,473	$ 9,262
Residential Loans Held for Investment \| ARM Loans \| Range 5
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum
Loan Balance, maximum	$ 1,000	$ 1,000
Interest Rate, minimum	0.00%	0.00%
Interest Rate, maximum	2.63%	2.63%
Number of loans \| loan	109	132
Principal value	$ 169,492	$ 207,539
30-89 Days DQ	1,341	2,494
90+ Days DQ	$ 14,718	$ 16,106
Residential Loans Held for Investment \| Hybrid ARM Loans
Mortgage Loans on Real Estate [Line Items]
Number of loans \| loan	41	70
Principal value	$ 20,827	$ 46,310
90+ Days DQ	0	319
Residential Loans Held for Investment \| Hybrid ARM Loans \| Range 1
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum	0	0
Loan Balance, maximum	$ 250	$ 250
Interest Rate, minimum	2.75%	2.63%
Interest Rate, maximum	2.88%	2.63%
Number of loans \| loan	3	3
Principal value	$ 317	$ 364
Residential Loans Held for Investment \| Hybrid ARM Loans \| Range 2
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum	251	251
Loan Balance, maximum	$ 500	$ 500
Interest Rate, minimum	2.63%	2.50%
Interest Rate, maximum	2.88%	5.15%
Number of loans \| loan	20	26
Principal value	$ 7,523	$ 10,056
90+ Days DQ	0	319
Residential Loans Held for Investment \| Hybrid ARM Loans \| Range 3
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum	501	501
Loan Balance, maximum	$ 750	$ 750
Interest Rate, minimum	2.63%	2.50%
Interest Rate, maximum	2.88%	4.65%
Number of loans \| loan	15	23
Principal value	$ 9,874	$ 14,711
Residential Loans Held for Investment \| Hybrid ARM Loans \| Range 4
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum	751	751
Loan Balance, maximum	$ 1,000	$ 1,000
Interest Rate, minimum	2.75%	2.50%
Interest Rate, maximum	2.75%	4.80%
Number of loans \| loan	2	11
Principal value	$ 1,547	$ 9,393
Residential Loans Held for Investment \| Hybrid ARM Loans \| Range 5
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum
Loan Balance, maximum	$ 1,000	$ 1,000
Interest Rate, minimum	2.75%	2.50%
Interest Rate, maximum	2.75%	4.95%
Number of loans \| loan	1	7
Principal value	$ 1,566	$ 11,786
Residential Loans Held for Investment \| Fixed Loans
Mortgage Loans on Real Estate [Line Items]
Number of loans \| loan		182
Principal value		$ 125,389
90+ Days DQ		726
Residential Loans Held for Investment \| Fixed Loans \| Range 1
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum		0
Loan Balance, maximum		$ 250
Interest Rate, minimum		3.70%
Interest Rate, maximum		4.90%
Number of loans \| loan		7
Principal value		$ 1,040
Residential Loans Held for Investment \| Fixed Loans \| Range 2
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum		251
Loan Balance, maximum		$ 500
Interest Rate, minimum		3.45%
Interest Rate, maximum		5.13%
Number of loans \| loan		42
Principal value		$ 17,574
Residential Loans Held for Investment \| Fixed Loans \| Range 3
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum		501
Loan Balance, maximum		$ 750
Interest Rate, minimum		3.65%
Interest Rate, maximum		5.25%
Number of loans \| loan		71
Principal value		$ 42,609
Residential Loans Held for Investment \| Fixed Loans \| Range 4
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum		751
Loan Balance, maximum		$ 1,000
Interest Rate, minimum		4.20%
Interest Rate, maximum		5.25%
Number of loans \| loan		38
Principal value		$ 32,966
90+ Days DQ		$ 726
Residential Loans Held for Investment \| Fixed Loans \| Range 5
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum
Loan Balance, maximum		$ 1,000
Interest Rate, minimum		4.30%
Interest Rate, maximum		5.38%
Number of loans \| loan		24
Principal value		$ 31,200
Residential Loans Held For Sale
Mortgage Loans on Real Estate [Line Items]
Number of loans \| loan	1,772	2,282
Principal value	$ 1,091,518	$ 1,305,493
30-89 Days DQ	4,346	1,348
90+ Days DQ	1,852	471
Residential Loans Held For Sale \| ARM Loans
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum	64	66
Loan Balance, maximum	$ 1,298	$ 359
Interest Rate, minimum	1.50%	1.88%
Interest Rate, maximum	4.00%	2.25%
Number of loans \| loan	14	8
Principal value	$ 5,258	$ 1,286
30-89 Days DQ	0	170
90+ Days DQ	415	471
Residential Loans Held For Sale \| Hybrid ARM Loans
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum	164	252
Loan Balance, maximum	$ 1,989	$ 1,985
Interest Rate, minimum	2.50%	2.63%
Interest Rate, maximum	4.25%	4.00%
Number of loans \| loan	356	109
Principal value	$ 276,457	$ 84,271
30-89 Days DQ	2,249
Residential Loans Held For Sale \| Fixed Loans
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum	30	75
Loan Balance, maximum	$ 2,332	$ 2,496
Interest Rate, minimum	2.75%	2.88%
Interest Rate, maximum	5.25%	5.00%
Number of loans \| loan	1,402	2,165
Principal value	$ 809,803	$ 1,219,936
30-89 Days DQ	2,097	$ 1,178
90+ Days DQ	$ 1,437
Residential Loans Held For Investment at Fair Value
Mortgage Loans on Real Estate [Line Items]
Number of loans \| loan	2,398	804
Principal value	$ 1,758,990	$ 566,372
30-89 Days DQ	$ 5,357	2,137
Residential Loans Held For Investment at Fair Value \| ARM Loans
Mortgage Loans on Real Estate [Line Items]
Number of loans \| loan	5
Principal value	$ 3,501
Residential Loans Held For Investment at Fair Value \| ARM Loans \| Range 1
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum	251
Loan Balance, maximum	$ 500
Interest Rate, minimum	3.63%
Interest Rate, maximum	3.75%
Number of loans \| loan	2
Principal value	$ 563
Residential Loans Held For Investment at Fair Value \| ARM Loans \| Range 2
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum	501
Loan Balance, maximum	$ 750
Interest Rate, minimum	3.50%
Interest Rate, maximum	3.50%
Number of loans \| loan	2
Principal value	$ 1,671
30-89 Days DQ	0
Residential Loans Held For Investment at Fair Value \| ARM Loans \| Range 3
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum	751
Loan Balance, maximum	$ 1,000
Interest Rate, minimum	3.63%
Interest Rate, maximum	3.63%
Number of loans \| loan	1
Principal value	$ 1,267
Residential Loans Held For Investment at Fair Value \| Hybrid ARM Loans
Mortgage Loans on Real Estate [Line Items]
30-89 Days DQ	542
Residential Loans Held For Investment at Fair Value \| Hybrid ARM Loans \| Range 1
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum	251	251
Loan Balance, maximum	$ 500	$ 500
Interest Rate, minimum	2.88%	2.38%
Interest Rate, maximum	3.88%	3.75%
Number of loans \| loan	7	29
Principal value	$ 2,963	$ 12,487
30-89 Days DQ	0
Residential Loans Held For Investment at Fair Value \| Hybrid ARM Loans \| Range 2
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum	501	501
Loan Balance, maximum	$ 750	$ 750
Interest Rate, minimum	2.63%	2.38%
Interest Rate, maximum	4.90%	4.25%
Number of loans \| loan	28	80
Principal value	$ 17,514	$ 49,085
30-89 Days DQ	0	619
Residential Loans Held For Investment at Fair Value \| Hybrid ARM Loans \| Range 3
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum	751	751
Loan Balance, maximum	$ 1,000	$ 1,000
Interest Rate, minimum	2.75%	2.38%
Interest Rate, maximum	5.05%	3.75%
Number of loans \| loan	15	51
Principal value	$ 12,994	$ 43,835
30-89 Days DQ	542
Residential Loans Held For Investment at Fair Value \| Hybrid ARM Loans \| Range 4
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum
Loan Balance, maximum	$ 1,000	$ 1,000
Interest Rate, minimum	2.88%	2.38%
Interest Rate, maximum	5.20%	3.25%
Number of loans \| loan	6	14
Principal value	$ 8,797	$ 17,720
30-89 Days DQ	$ 0
Residential Loans Held For Investment at Fair Value \| Hybrid ARM Loans \| Range 5
Mortgage Loans on Real Estate [Line Items]
Number of loans \| loan	56	174
Principal value	$ 42,268	$ 123,127
30-89 Days DQ	$ 0	$ 619
Residential Loans Held For Investment at Fair Value \| Fixed Loans
Mortgage Loans on Real Estate [Line Items]
Number of loans \| loan	2,337	630
Principal value	$ 1,713,221	$ 443,245
30-89 Days DQ	5,357	1,518
Residential Loans Held For Investment at Fair Value \| Fixed Loans \| Range 1
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum	0	0
Loan Balance, maximum	$ 250	$ 250
Interest Rate, minimum	3.64%	4.13%
Interest Rate, maximum	5.38%	4.13%
Number of loans \| loan	29	1
Principal value	$ 5,295	$ 75
30-89 Days DQ	242
Residential Loans Held For Investment at Fair Value \| Fixed Loans \| Range 2
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum	251	251
Loan Balance, maximum	$ 500	$ 500
Interest Rate, minimum	3.13%	3.13%
Interest Rate, maximum	5.13%	4.75%
Number of loans \| loan	484	158
Principal value	$ 212,732	$ 72,931
30-89 Days DQ	913	894
Residential Loans Held For Investment at Fair Value \| Fixed Loans \| Range 3
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum	501	501
Loan Balance, maximum	$ 750	$ 750
Interest Rate, minimum	2.94%	3.13%
Interest Rate, maximum	5.25%	5.00%
Number of loans \| loan	959	272
Principal value	$ 595,863	$ 165,574
30-89 Days DQ	3,213	624
Residential Loans Held For Investment at Fair Value \| Fixed Loans \| Range 4
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum	751	751
Loan Balance, maximum	$ 1,000	$ 1,000
Interest Rate, minimum	2.90%	3.13%
Interest Rate, maximum	5.00%	4.88%
Number of loans \| loan	552	136
Principal value	$ 480,557	$ 116,892
30-89 Days DQ	$ 989
Residential Loans Held For Investment at Fair Value \| Fixed Loans \| Range 5
Mortgage Loans on Real Estate [Line Items]
Loan Balance, minimum
Loan Balance, maximum	$ 1,000	$ 1,000
Interest Rate, minimum	3.14%	3.25%
Interest Rate, maximum	5.00%	5.00%
Number of loans \| loan	313	63
Principal value	$ 418,774	$ 87,773
30-89 Days DQ	$ 0

Residential Loans - Loan Product Type and Accompanying Loan Characteristics of Residential Loans (Detail)
$ in Thousands

12 Months Ended

Dec. 31, 2015

USD ($)

loan

Dec. 31, 2014

USD ($)

loan

Residential Loans Held for Investment

Mortgage Loans on Real Estate [Line Items]

Number of loans | loan

4,545