Fair Value - Summary of Financial Statement Items Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Assets:
Short-term investments at fair value	$ 76,731		$ 74,850
Mortgage-backed securities at fair value pledged to creditors	2,600,357		2,610,422
Loans acquired for sale at fair value	2,477,267		1,643,957
Excess servicing spread purchased from PFSI	194,156		216,110
Derivative and credit risk transfer strip assets:
Derivative assets	219,626		171,996
Derivative assets, Netting	(23,323)		(4,831)
Total derivative and credit risk transfer strip assets after netting	196,303		167,165
Firm commitment to purchase credit risk transfer securities at fair value	15,581		37,994
Mortgage servicing rights at fair value	1,126,427	$ 1,156,908	1,162,369	$ 1,010,507	$ 957,013	$ 91,459
Liabilities:
Asset-backed financing of a VIE at fair value	270,077		276,499
Interest-only security payable at fair value	26,356		36,011
Derivative liabilities:
Derivative liabilities	27,306		29,490
Derivative liabilities, Netting	(4,852)		(23,576)
Total derivative liabilities after netting	22,454		5,914
CRT Agreements [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	124,033		123,987
Derivative assets, Netting	0		0
Total derivative and credit risk transfer strip assets after netting	124,033		123,987
Derivative liabilities:
Derivative liabilities	0		0
Interest Rate Lock Commitments [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	14,816		12,162
Total derivative and credit risk transfer strip assets after netting	14,816		12,162
Derivative liabilities:
Derivative liabilities	1,202		174
Forward Purchase Contracts [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	34,285		14,845
Derivative assets, Netting	0		0
Total derivative and credit risk transfer strip assets after netting	34,285		14,845
Derivative liabilities:
Derivative liabilities	4,052		43
Derivative liabilities, Netting	0		0
Forward Sales Contracts [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	3,074		13
Derivative assets, Netting	0		0
Total derivative and credit risk transfer strip assets after netting	3,074		13
Derivative liabilities:
Derivative liabilities	22,052		29,273
Derivative liabilities, Netting	0		0
MBS Put Options [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	8,620		218
Derivative assets, Netting	0		0
Total derivative and credit risk transfer strip assets after netting	8,620		218
Derivative liabilities:
Derivative liabilities	0		0
MBS Call Options [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	4,332		945
Derivative assets, Netting	0		0
Total derivative and credit risk transfer strip assets after netting	4,332		945
Derivative liabilities:
Derivative liabilities	0		0
Call Options on Interest Rate Futures [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	16,863		5,137
Derivative assets, Netting	0		0
Total derivative and credit risk transfer strip assets after netting	16,863		5,137
Derivative liabilities:
Derivative liabilities	0		0
Put Options on Interest Rate Futures [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	1,557		178
Derivative assets, Netting	0		0
Total derivative and credit risk transfer strip assets after netting	1,557		178
Derivative liabilities:
Derivative liabilities	0		0
Repurchase Agreement Derivatives [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	12,046		14,511
Derivative assets, Netting	0		0
Total derivative and credit risk transfer strip assets after netting	12,046		14,511
Derivative liabilities:
Derivative liabilities	0		0
Recurring [Member]
Assets:
Short-term investments at fair value	76,731		74,850
Mortgage-backed securities at fair value pledged to creditors	2,600,357		2,610,422
Loans acquired for sale at fair value	2,477,267		1,643,957
Loans at fair value	358,570		408,305
Excess servicing spread purchased from PFSI	194,156		216,110
Derivative and credit risk transfer strip assets:
Derivative assets	282,105		171,996
Derivative assets, Netting	(23,323)		(4,831)
Total derivative and credit risk transfer strip assets after netting	258,782		167,165
Firm commitment to purchase credit risk transfer securities at fair value	15,581		37,994
Mortgage servicing rights at fair value	1,126,427		1,162,369
Total Assets	7,107,871		6,321,172
Liabilities:
Asset-backed financing of a VIE at fair value	270,077		276,499
Interest-only security payable at fair value	26,356		36,011
Derivative liabilities:
Derivative liabilities	27,306		29,490
Derivative liabilities, Netting	(4,852)		(23,576)
Total derivative liabilities after netting	22,454		5,914
Total liabilities	318,887		318,424
Recurring [Member] | Credit Risk Transfer Strips
Derivative and credit risk transfer strip assets:
Derivative assets	62,479
Recurring [Member] | CRT Agreements [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	124,033		123,987
Recurring [Member] | Interest Rate Lock Commitments [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	14,816		12,162
Derivative liabilities:
Derivative liabilities	1,202		174
Recurring [Member] | Forward Purchase Contracts [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	34,285		14,845
Derivative liabilities:
Derivative liabilities	4,052		43
Recurring [Member] | Forward Sales Contracts [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	3,074		13
Derivative liabilities:
Derivative liabilities	22,052		29,273
Recurring [Member] | Level 1 [Member]
Assets:
Short-term investments at fair value	76,731		74,850
Mortgage-backed securities at fair value pledged to creditors	0		0
Loans acquired for sale at fair value	0		0
Loans at fair value	0		0
Excess servicing spread purchased from PFSI	0		0
Derivative and credit risk transfer strip assets:
Derivative assets	18,420		5,315
Derivative assets, Netting	0		0
Total derivative and credit risk transfer strip assets after netting	18,420		5,315
Firm commitment to purchase credit risk transfer securities at fair value	0		0
Mortgage servicing rights at fair value	0		0
Total Assets	95,151		80,165
Liabilities:
Asset-backed financing of a VIE at fair value	0		0
Interest-only security payable at fair value	0		0
Derivative liabilities:
Derivative liabilities	0		0
Derivative liabilities, Netting	0		0
Total derivative liabilities after netting	0		0
Total liabilities	0		0
Recurring [Member] | Level 1 [Member] | Credit Risk Transfer Strips
Derivative and credit risk transfer strip assets:
Derivative assets	0
Recurring [Member] | Level 1 [Member] | CRT Agreements [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	0		0
Recurring [Member] | Level 1 [Member] | Interest Rate Lock Commitments [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	0		0
Derivative liabilities:
Derivative liabilities	0		0
Recurring [Member] | Level 1 [Member] | Forward Purchase Contracts [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	0		0
Derivative liabilities:
Derivative liabilities	0		0
Recurring [Member] | Level 1 [Member] | Forward Sales Contracts [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	0		0
Derivative liabilities:
Derivative liabilities	0		0
Recurring [Member] | Level 2 [Member]
Assets:
Short-term investments at fair value	0		0
Mortgage-backed securities at fair value pledged to creditors	2,600,357		2,610,422
Loans acquired for sale at fair value	2,463,079		1,626,483
Loans at fair value	284,097		290,573
Excess servicing spread purchased from PFSI	0		0
Derivative and credit risk transfer strip assets:
Derivative assets	50,311		16,021
Derivative assets, Netting	0		0
Total derivative and credit risk transfer strip assets after netting	50,311		16,021
Firm commitment to purchase credit risk transfer securities at fair value	0		0
Mortgage servicing rights at fair value	0		0
Total Assets	5,397,844		4,543,499
Liabilities:
Asset-backed financing of a VIE at fair value	270,077		276,499
Interest-only security payable at fair value	0		0
Derivative liabilities:
Derivative liabilities	26,104		29,316
Derivative liabilities, Netting	0		0
Total derivative liabilities after netting	26,104		29,316
Total liabilities	296,181		305,815
Recurring [Member] | Level 2 [Member] | Credit Risk Transfer Strips
Derivative and credit risk transfer strip assets:
Derivative assets	0
Recurring [Member] | Level 2 [Member] | CRT Agreements [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	0		0
Recurring [Member] | Level 2 [Member] | Interest Rate Lock Commitments [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	0		0
Derivative liabilities:
Derivative liabilities	0		0
Recurring [Member] | Level 2 [Member] | Forward Purchase Contracts [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	34,285		14,845
Derivative liabilities:
Derivative liabilities	4,052		43
Recurring [Member] | Level 2 [Member] | Forward Sales Contracts [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	3,074		13
Derivative liabilities:
Derivative liabilities	22,052		29,273
Recurring [Member] | Level 3 [Member]
Assets:
Short-term investments at fair value	0		0
Mortgage-backed securities at fair value pledged to creditors	0		0
Loans acquired for sale at fair value	14,188		17,474
Loans at fair value	74,473		117,732
Excess servicing spread purchased from PFSI	194,156		216,110
Derivative and credit risk transfer strip assets:
Derivative assets	213,374		150,660
Derivative assets, Netting	0		0
Total derivative and credit risk transfer strip assets after netting	213,374		150,660
Firm commitment to purchase credit risk transfer securities at fair value	15,581		37,994
Mortgage servicing rights at fair value	1,126,427		1,162,369
Total Assets	1,638,199		1,702,339
Liabilities:
Asset-backed financing of a VIE at fair value	0		0
Interest-only security payable at fair value	26,356		36,011
Derivative liabilities:
Derivative liabilities	1,202		174
Derivative liabilities, Netting	0		0
Total derivative liabilities after netting	1,202		174
Total liabilities	27,558		36,185
Recurring [Member] | Level 3 [Member] | Credit Risk Transfer Strips
Derivative and credit risk transfer strip assets:
Derivative assets	62,479
Recurring [Member] | Level 3 [Member] | CRT Agreements [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	124,033		123,987
Recurring [Member] | Level 3 [Member] | Interest Rate Lock Commitments [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	14,816		12,162
Derivative liabilities:
Derivative liabilities	1,202		174
Recurring [Member] | Level 3 [Member] | Forward Purchase Contracts [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	0		0
Derivative liabilities:
Derivative liabilities	0		0
Recurring [Member] | Level 3 [Member] | Forward Sales Contracts [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	0		0
Derivative liabilities:
Derivative liabilities	0		0
Recurring [Member] | MBS Put Options [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	8,620		218
Recurring [Member] | MBS Put Options [Member] | Level 1 [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	0		0
Recurring [Member] | MBS Put Options [Member] | Level 2 [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	8,620		218
Recurring [Member] | MBS Put Options [Member] | Level 3 [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	0		0
Recurring [Member] | MBS Call Options [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	4,332		945
Recurring [Member] | MBS Call Options [Member] | Level 1 [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	0		0
Recurring [Member] | MBS Call Options [Member] | Level 2 [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	4,332		945
Recurring [Member] | MBS Call Options [Member] | Level 3 [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	0		0
Recurring [Member] | Call Options on Interest Rate Futures [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	16,863		5,137
Recurring [Member] | Call Options on Interest Rate Futures [Member] | Level 1 [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	16,863		5,137
Recurring [Member] | Call Options on Interest Rate Futures [Member] | Level 2 [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	0		0
Recurring [Member] | Call Options on Interest Rate Futures [Member] | Level 3 [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	0		0
Recurring [Member] | Put Options on Interest Rate Futures [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	1,557		178
Recurring [Member] | Put Options on Interest Rate Futures [Member] | Level 1 [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	1,557		178
Recurring [Member] | Put Options on Interest Rate Futures [Member] | Level 2 [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	0		0
Recurring [Member] | Put Options on Interest Rate Futures [Member] | Level 3 [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	0		0
Recurring [Member] | Repurchase Agreement Derivatives [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	12,046		14,511
Recurring [Member] | Repurchase Agreement Derivatives [Member] | Level 1 [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	0		0
Recurring [Member] | Repurchase Agreement Derivatives [Member] | Level 2 [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	0		0
Recurring [Member] | Repurchase Agreement Derivatives [Member] | Level 3 [Member]
Derivative and credit risk transfer strip assets:
Derivative assets	$ 12,046		$ 14,511