Investments - Narrative (Details)	3 Months Ended
Mar. 31, 2021 USD ($) security	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($) security
Investments available for sale
Number of investment securities in an unrealized loss position \| security	802		363
Other-than-temporary impairments	$ 0	$ 0
Other invested assets	100,393,000		$ 88,904,000
Fair value of investments deposited with insurance regulatory authorities	9,400,000		9,700,000
Essent Re
Investments available for sale
Fair value of the required investments on deposit in trusts	1,200,000,000		1,100,000,000
Essent Guaranty
Investments available for sale
Assets on deposit under reinsurance agreement	8,500,000		8,500,000
Assets on deposit for the benefit of the sponsor	$ 12,000,000.0		$ 12,000,000.0
Securities \| Credit Concentration Risk \| Internal Investment Grade
Investments available for sale
Concentration risk, percentage	98.00%

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Assets on Deposit Under Reinsurance Agreements

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The total amount of cash and securities held by third party trustees pursuant to terms of debt instruments or other agreements as of the date of each statement of financial position presented, which can be used by the trustee only to pay the noncurrent portion of specified obligations.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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Amount of restricted investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

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Amount of other-than-temporary impairment (OTTI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), recognized in earnings.

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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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