Stock-based Compensation - Compensation Expense by Award (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
Apr. 30, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock-Based Compensation
Units available for future awards under 2013 Equity Incentive Plan (in units)		3,900,000
Stock-based compensation expense		$ 25,251	$ 20,697	$ 16,505
Stock Options
Stock-Based Compensation
Granted (in units)		674,000	861,000	962,000
Stock-based compensation expense		$ 6,218	$ 4,909	$ 4,464
Performance-based RSUs
Stock-Based Compensation
Granted (in units)		524,000	694,000	813,000
Vested (in units)	649,000	730,000	446,000
Stock-based compensation expense		$ 12,425	$ 11,020	$ 9,475
Time-based RSUs
Stock-Based Compensation
Granted (in units)		328,000	408,000	261,000
Vested (in units)		254,000	173,000	127,000
Stock-based compensation expense		$ 6,608	$ 4,768	$ 2,494
Exchangeable PNMAC Units
Stock-Based Compensation
Stock-based compensation expense				$ 72

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Gross number of share options (or share units) granted during the period.

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