Investments - Summary of Realized Gain and Loss and Investments in Unrealized Loss Position (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) security	Dec. 31, 2019 USD ($) security	Dec. 31, 2018 USD ($)
Debt Securities, Available-for-sale [Line Items]
Realized gross gains	$ 5,608,000	$ 5,238,000	$ 2,201,000
Realized gross losses	2,482,000	1,746,000	883,000
Fair Value
Less than 12 months	614,451,000	372,179,000
12 months or more	78,420,000	310,585,000
Total	692,871,000	682,764,000
Gross Unrealized Losses
Less than 12 months	(2,618,000)	(3,369,000)
12 months or more	(1,122,000)	(2,700,000)
Total	$ (3,740,000)	$ (6,069,000)
Other Information
Number of investment securities in unrealized loss position | security	363	365
Other-than-temporary impairment	$ 400,000	$ 300,000	$ 0
Other invested assets	88,904,000	78,873,000
Fair value of investments deposited with insurance regulatory authorities to meet statutory requirements	$ 9,700,000	9,400,000
Internal Investment Grade | Securities | Credit Concentration Risk
Other Information
Concentration risk, percentage	98.00%
Essent Re
Other Information
Fair value of the required investments on deposit in trusts	$ 1,100,000,000	805,500,000
Essent Guaranty
Other Information
Assets on deposit under reinsurance agreement	8,500,000	6,400,000
Assets on deposit for the benefit of the sponsor	12,000,000.0	6,400,000
U.S. Treasury securities
Fair Value
Less than 12 months	28,776,000	29,013,000
12 months or more	0	42,981,000
Total	28,776,000	71,994,000
Gross Unrealized Losses
Less than 12 months	(22,000)	(331,000)
12 months or more	0	(76,000)
Total	(22,000)	(407,000)
U.S. agency securities
Fair Value
Less than 12 months		0
12 months or more		25,605,000
Total		25,605,000
Gross Unrealized Losses
Less than 12 months		0
12 months or more		(51,000)
Total		(51,000)
U.S. agency mortgage-backed securities
Fair Value
Less than 12 months	152,671,000	101,684,000
12 months or more	3,007,000	113,866,000
Total	155,678,000	215,550,000
Gross Unrealized Losses
Less than 12 months	(924,000)	(1,042,000)
12 months or more	(46,000)	(1,290,000)
Total	(970,000)	(2,332,000)
Municipal debt securities
Fair Value
Less than 12 months	3,838,000	10,651,000
12 months or more	0	624,000
Total	3,838,000	11,275,000
Gross Unrealized Losses
Less than 12 months	(15,000)	(112,000)
12 months or more	0	(6,000)
Total	(15,000)	(118,000)
Non-U.S. government securities
Fair Value
Less than 12 months		9,664,000
12 months or more		0
Total		9,664,000
Gross Unrealized Losses
Less than 12 months		(47,000)
12 months or more		0
Total		(47,000)
Corporate debt securities
Fair Value
Less than 12 months	141,803,000	83,013,000
12 months or more	0	14,531,000
Total	141,803,000	97,544,000
Gross Unrealized Losses
Less than 12 months	(379,000)	(576,000)
12 months or more	0	(16,000)
Total	(379,000)	(592,000)
Residential and commercial mortgage securities
Fair Value
Less than 12 months	63,203,000	59,341,000
12 months or more	9,516,000	3,442,000
Total	72,719,000	62,783,000
Gross Unrealized Losses
Less than 12 months	(777,000)	(1,059,000)
12 months or more	(503,000)	(42,000)
Total	(1,280,000)	(1,101,000)
Asset-backed securities
Fair Value
Less than 12 months	124,165,000	78,813,000
12 months or more	65,897,000	109,536,000
Total	190,062,000	188,349,000
Gross Unrealized Losses
Less than 12 months	(483,000)	(202,000)
12 months or more	(573,000)	(1,219,000)
Total	(1,056,000)	$ (1,421,000)
Money market funds
Fair Value
Less than 12 months	99,995,000
12 months or more	0
Total	99,995,000
Gross Unrealized Losses
Less than 12 months	(18,000)
12 months or more	0
Total	$ (18,000)