Investments Available for Sale (Details 4) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Realized gross gains	$ 518,000	$ 749,000	$ 1,309,000	$ 1,430,000
Realized gross losses	79,000	205,000	673,000	231,000
Fair Value
Less than 12 months	1,419,428,000		1,419,428,000		$ 835,553,000
12 months or more	401,020,000		401,020,000		432,761,000
Total	1,820,448,000		1,820,448,000		1,268,314,000
Gross Unrealized Losses
Less than 12 months	28,217,000		28,217,000		5,177,000
12 months or more	20,909,000		20,909,000		11,846,000
Total	49,126,000		49,126,000		17,023,000
Other Information
Other-than-temporary impairments	0	$ 0	0	$ 0
Fair value of investments deposited with insurance regularoty authorities	8,600,000		8,600,000		8,600,000
U.S. Treasury securities
Fair Value
Less than 12 months	132,201,000		132,201,000		151,119,000
12 months or more	61,975,000		61,975,000		69,454,000
Total	194,176,000		194,176,000		220,573,000
Gross Unrealized Losses
Less than 12 months	3,722,000		3,722,000		1,240,000
12 months or more	4,522,000		4,522,000		2,862,000
Total	8,244,000		8,244,000		4,102,000
Municipal debt securities
Fair Value
Less than 12 months	252,919,000		252,919,000		124,171,000
12 months or more	22,679,000		22,679,000		23,492,000
Total	275,598,000		275,598,000		147,663,000
Gross Unrealized Losses
Less than 12 months	4,180,000		4,180,000		817,000
12 months or more	772,000		772,000		444,000
Total	4,952,000		4,952,000		1,261,000
Non-U.S. government securities:
Fair Value
Less than 12 months	20,516,000		20,516,000
12 months or more	0		0
Total	20,516,000		20,516,000
Gross Unrealized Losses
Less than 12 months	293,000		293,000
12 months or more	0		0
Total	293,000		293,000
Corporate debt securities
Fair Value
Less than 12 months	517,897,000		517,897,000		214,371,000
12 months or more	88,857,000		88,857,000		94,261,000
Total	606,754,000		606,754,000		308,632,000
Gross Unrealized Losses
Less than 12 months	11,324,000		11,324,000		1,213,000
12 months or more	3,497,000		3,497,000		1,824,000
Total	14,821,000		14,821,000		3,037,000
Residential and commercial mortgage securities
Fair Value
Less than 12 months	42,432,000		42,432,000		29,842,000
12 months or more	5,881,000		5,881,000		5,988,000
Total	48,313,000		48,313,000		35,830,000
Gross Unrealized Losses
Less than 12 months	495,000		495,000		179,000
12 months or more	355,000		355,000		179,000
Total	850,000		850,000		358,000
Asset-backed securities
Fair Value
Less than 12 months	169,257,000		169,257,000		58,798,000
12 months or more	8,210,000		8,210,000		5,828,000
Total	177,467,000		177,467,000		64,626,000
Gross Unrealized Losses
Less than 12 months	873,000		873,000		133,000
12 months or more	79,000		79,000		50,000
Total	952,000		952,000		183,000
Money market funds
Fair Value
Less than 12 months					59,489,000
12 months or more					0
Total					59,489,000
Gross Unrealized Losses
Less than 12 months					11,000
12 months or more					0
Total					11,000
U.S. Agency | U.S. agency securities
Fair Value
Less than 12 months	17,097,000		17,097,000		17,320,000
12 months or more	15,658,000		15,658,000		15,794,000
Total	32,755,000		32,755,000		33,114,000
Gross Unrealized Losses
Less than 12 months	407,000		407,000		190,000
12 months or more	495,000		495,000		365,000
Total	902,000		902,000		555,000
U.S. Agency | U.S. agency mortgage-backed securities
Fair Value
Less than 12 months	267,109,000		267,109,000		180,443,000
12 months or more	197,760,000		197,760,000		217,944,000
Total	464,869,000		464,869,000		398,387,000
Gross Unrealized Losses
Less than 12 months	6,923,000		6,923,000		1,394,000
12 months or more	11,189,000		11,189,000		6,122,000
Total	18,112,000		18,112,000		7,516,000
Essent Re
Other Information
Fair value of the required investments on deposit in trusts	729,000,000		729,000,000		$ 615,800,000
Essent Guaranty
Other Information
Deposit assets	$ 3,300,000		$ 3,300,000