Earnings Per Share of Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended								12 Months Ended
	Nov. 01, 2018	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Basic earnings per share of common stock:
Net income attributable to common stockholders		$ 38,749	$ 14,489	$ 17,837	$ 16,619	$ 62,318	$ 17,081	$ 10,479	$ 10,879	$ 87,694	$ 100,757	$ 66,079
Weighted-average common stock outstanding										33,524,000	23,199,000	22,161,000
Basic earnings per share of common stock (in dollars per share)		$ 0.65	$ 0.58	$ 0.71	$ 0.70	$ 2.67	$ 0.73	$ 0.45	$ 0.48	$ 2.62	$ 4.34	$ 2.98
Diluted earnings per share of common stock:
Net income attributable to common stockholders		$ 38,749	$ 14,489	$ 17,837	$ 16,619	$ 62,318	$ 17,081	$ 10,479	$ 10,879	$ 87,694	$ 100,757	$ 66,079
Net income attributable to dilutive stock-based compensation units										3,868
Effect of net income attributable to noncontrolling interest, net of tax												159,570
Net income attributable to common stockholders for diluted earnings per share										$ 91,562	$ 100,757	$ 225,649
Weighted-average common stock outstanding applicable to basic earnings per share										33,524,000	23,199,000	22,161,000
Effect of dilutive shares:
PennyMac Class A units exchangeable to common stock												53,951,000
Shares issuable under stock-based compensation plans (in shares)										1,798,000	1,800,000	517,000
Weighted-average shares of common stock outstanding applicable to diluted earnings per share										35,322,000	24,999,000	76,629,000
Diluted earnings per share of common stock (in dollars per share)		$ 0.63	$ 0.57	$ 0.70	$ 0.67	$ 2.44	$ 0.71	$ 0.44	$ 0.47	$ 2.59	$ 4.03	$ 2.94
Total anti-dilutive stock-based compensation units										45,527	55,119	3,883
Weighted-average exercise price of anti-dilutive stock options										$ 17.81	$ 16.40	$ 15.81
Performance-based RSUs
Effect of dilutive shares:
Total anti-dilutive stock-based compensation units										1,084	497	2,054
Stock Options
Effect of dilutive shares:
Total anti-dilutive stock-based compensation units										740	1,323	1,829
Exchangeable PNMAC Units
Effect of dilutive shares:
Total anti-dilutive stock-based compensation units										43,700	53,299
Time-based RSUs
Effect of dilutive shares:
Total anti-dilutive stock-based compensation units										3
Class A Unit | New PFSI
Common stock conversion ratio (as a percent)	100.00%