Earnings Per Share of Common Stock (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended								12 Months Ended
	Nov. 01, 2018	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Basic earnings per share of common stock:
Net income attributable to common stockholders		$ 152,661	$ 121,473	$ 72,696	$ 46,135	$ 38,749	$ 14,489	$ 17,837	$ 16,619	$ 392,965	$ 87,694	$ 100,757
Weighted-average common stock outstanding (in shares)										78,206	33,524	23,199
Basic earnings per share of common stock (in dollars per share)		$ 1.95	$ 1.55	$ 0.93	$ 0.59	$ 0.65	$ 0.58	$ 0.71	$ 0.70	$ 5.02	$ 2.62	$ 4.34
Diluted earnings per share of common stock:
Net income attributable to common stockholders		$ 152,661	$ 121,473	$ 72,696	$ 46,135	$ 38,749	$ 14,489	$ 17,837	$ 16,619	$ 392,965	$ 87,694	$ 100,757
Net income attributable to dilutive stock-based compensation units											3,868
Net income attributable to common stockholders for diluted earnings per share										$ 392,965	$ 91,562	$ 100,757
Weighted-average common stock outstanding applicable to basic earnings per share (in shares)										78,206	33,524	23,199
Effect of dilutive shares:
Common shares issuable under stock-based compensation plans (in shares)										2,134	1,798	1,800
Weighted-average shares of common stock applicable to diluted earnings per share (in shares)										80,340	35,322	24,999
Diluted earnings per share of common stock (in dollars per share)		$ 1.88	$ 1.51	$ 0.92	$ 0.58	$ 0.63	$ 0.57	$ 0.70	$ 0.67	$ 4.89	$ 2.59	$ 4.03
Total anti-dilutive shares and units (in shares)										1,604	45,527	55,119
Weighted-average exercise price of anti-dilutive stock options (in dollars per share)										$ 23.70	$ 17.81	$ 16.40
Performance-based RSUs
Effect of dilutive shares:
Total anti-dilutive shares and units (in shares)										1,032	1,084	497
Time-based RSUs
Effect of dilutive shares:
Total anti-dilutive shares and units (in shares)											3
Stock Options
Effect of dilutive shares:
Total anti-dilutive shares and units (in shares)										572	740	1,323
Exchangeable PNMAC Units
Effect of dilutive shares:
Total anti-dilutive shares and units (in shares)											43,700	53,299
Class A Unit | New PFSI
Common stock conversion ratio (as a percent)	100.00%