Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2016
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of financial statements in accordance with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting periods. Actual results could differ from those estimates.
Investments Available for Sale	Investments Available for Sale Investments available for sale include securities that we sell from time to time to provide liquidity and in response to changes in the market. Debt and equity securities classified as available for sale are reported at fair value with unrealized gains and losses on these securities reported in other comprehensive income, net of deferred income taxes. See Note 16 for a description of the valuation methods for investments available for sale. We monitor our fixed maturities for unrealized losses that appear to be other-than-temporary. A fixed maturity security is considered to be other-than-temporarily impaired when the security's fair value is less than its amortized cost basis and 1) we intend to sell the security, 2) it is more likely than not that we will be required to sell the security before recovery of the security's amortized cost basis, or 3) we believe we will be unable to recover the entire amortized cost basis of the security (i.e., a credit loss has occurred). When we determine that a credit loss has been incurred, but we do not intend to sell the security and it is not more likely than not that we will be required to sell the security before recovery of the security's amortized cost basis, the portion of the other-than-temporary impairment that is credit related is recorded as a realized loss in the consolidated statements of comprehensive income, and the portion of the other-than-temporary impairment that is not credit related is included in other comprehensive income. For those fixed maturities for which an other-than-temporary impairment has occurred, we adjust the amortized cost basis of the security and record a realized loss in the consolidated statements of comprehensive income. We recognize purchase premiums and discounts in interest income using the interest method over the term of the securities. Gains and losses on the sales of securities are recorded on the trade date and are determined using the specific identification method. Short-term investments are defined as short-term, highly liquid investments, both readily convertible to cash and having maturities at acquisition of twelve months or less.
Long-Lived Assets	Long-Lived Assets Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation is calculated using the straight-line method over the estimated useful lives of the assets. Repairs and maintenance are charged to expense as incurred. Estimated useful lives are 5 years for furniture and fixtures and 2 to 3 years for equipment, computer hardware and purchased software. Certain costs associated with the acquisition or development of internal-use software are capitalized. Once the software is ready for its intended use, these costs are amortized on a straight-line basis over the software's expected useful life, which is generally 3 years.
Deferred Policy Acquisition Costs	Deferred Policy Acquisition Costs We defer certain personnel costs and premium tax expense directly related to the successful acquisition of new insurance policies and amortize these costs over the period the related estimated gross profits are recognized in order to match costs and revenues. We do not defer any underwriting costs associated with our contract underwriting services. Costs related to the acquisition of mortgage insurance business are initially deferred and reported as deferred policy acquisition costs. Consistent with industry accounting practice, amortization of these costs for each underwriting year book of business is recognized in proportion to estimated gross profits. Estimated gross profits are composed of earned premium, interest income, losses and loss adjustment expenses. The deferred costs are adjusted as appropriate for policy cancellations to be consistent with our revenue recognition policy. We estimate the rate of amortization to reflect actual experience and any changes to persistency or loss development. Deferred policy acquisition costs are reviewed periodically to determine that they do not exceed recoverable amounts, after considering investment income.
Insurance Premium Revenue Recognition	Insurance Premium Revenue Recognition Mortgage guaranty insurance policies are contracts that are generally non-cancelable by the insurer, are renewable at a fixed price, and provide for payment of premium on a monthly, annual or single basis. Upon renewal, we are not able to re-underwrite or re-price our policies. Consistent with industry accounting practices, premiums written on a monthly basis are earned as coverage is provided. Monthly policies accounted for 81% of earned premium in 2016. Premiums written on an annual basis are amortized on a pro rata basis over the year of coverage. Primary mortgage insurance written on policies covering more than one year are referred to as single premium policies. A portion of the revenue from single premium policies is recognized in earned premium in the current period, and the remaining portion is deferred as unearned premium and earned over the expected life of the policy. If single premium policies related to insured loans are cancelled due to repayment by the borrower, and the premium is non-refundable, then the remaining unearned premium related to each cancelled policy is recognized as earned premium upon notification of the cancellation. The Company recorded $36.9 million and $21.8 million of earned premium related to policy cancellations for the years ended December 31, 2016 and 2015, respectively. Unearned premium represents the portion of premium written that is applicable to the estimated unexpired risk of insured loans. Rates used to determine the earning of single premium policies are estimates based on an analysis of the expiration of risk. A significant portion of our premium revenue relates to master policies with certain lending institutions. For the year ended December 31, 2016 one lender represented 12% of our total revenue. The loss of this customer could have a significant impact on our revenues and results of operations.
Reserve for Losses and Loss Adjustment Expenses	Reserve for Losses and Loss Adjustment Expenses We establish reserves for losses based on our best estimate of ultimate claim costs for defaulted loans using the general principles contained in ASC No. 944, in accordance with industry practice. However, consistent with industry standards for mortgage insurers, we do not establish loss reserves for future claims on insured loans which are not currently in default. Loans are classified as in default when the borrower has missed two consecutive payments. Once we are notified that a borrower has defaulted, we will consider internal and third-party information and models, including the status of the loan as reported by its servicer and the type of loan product to determine the likelihood that a default will reach claim status. In addition, we will project the amount that we will pay if a default becomes a claim (referred to as "claim severity"). Based on this information, at each reporting date we determine our best estimate of loss reserves at a given point in time. Included in loss reserves are reserves for incurred but not reported ("IBNR") claims. IBNR reserves represent our estimated unpaid losses on loans that are in default, but have not yet been reported to us as delinquent by our customers. We will also establish reserves for associated loss adjustment expenses, consisting of the estimated cost of the claims administration process, including legal and other fees and expenses associated with administering the claims process. Establishing reserves is inherently subjective as it requires estimates that are susceptible to significant revision as more information becomes available. Our estimates of claim rates and claim sizes will be strongly influenced by prevailing economic conditions, such as the overall state of the economy, current rates or trends in unemployment, changes in housing values and/or interest rates, and our best judgments as to the future values or trends of these macroeconomic factors. Losses incurred are also generally affected by the characteristics of our insured loans, such as the loan amount, loan-to-value ratio, the percentage of coverage on the insured loan and the credit quality of the borrower.
Premium Deficiency Reserve	Premium Deficiency Reserve We are required to establish a premium deficiency reserve if the net present value of the expected future losses and expenses for a particular group of policies exceeds the net present value of expected future premium, anticipated investment income and existing reserves for that specified group of policies. We reassess our expectations for premium, losses and expenses of our mortgage insurance business periodically and update our premium deficiency analysis accordingly. As of December 31, 2016 and 2015, we concluded that no premium deficiency reserve was required to be recorded in the accompanying consolidated financial statements.
Derivative Instruments	Derivative Instruments Through June 30, 2016, insurance and certain reinsurance policies issued by Essent Re in connection with Freddie Mac's Agency Credit Insurance Structure ("ACIS") program were accounted for as derivatives under GAAP with the fair value of these policies reported as an asset or liability and changes in the fair value of these policies reported in earnings as a component of other income. During the quarter ended September 30, 2016, these contracts were amended and are now accounted for as insurance contracts rather than as derivatives. As of December 31, 2016, the Company had no derivative instruments.
Stock-Based Compensation	Stock-Based Compensation We measure the cost of employee services received in exchange for awards of equity instruments at the grant date of the award using a fair value based method. Prior to our initial public offering, we estimated the fair value of each nonvested share grant on the date of grant based on management's best estimate using methods further described in Note 10 of our consolidated financial statements. Subsequent to our initial public offering, fair value is determined on the date of grant based on quoted market prices. We recognize compensation expense on nonvested shares over the vesting period of the award.
Income Taxes	Income Taxes Deferred income tax assets and liabilities are determined using the asset and liability (or balance sheet) method. Under this method, we determine the net deferred tax asset or liability based on the tax effects of the temporary differences between the book and tax bases of the various assets and liabilities and give current recognition to changes in tax rates and laws. Changes in tax laws, rates, regulations and policies, or the final determination of tax audits or examinations, could materially affect our tax estimates. We evaluate the realizability of the deferred tax asset and recognize a valuation allowance if, based on the weight of all available positive and negative evidence, it is more likely than not that some portion or all of the deferred tax asset will not be realized. When evaluating the realizability of the deferred tax asset, we consider estimates of expected future taxable income, existing and projected book/tax differences, carryback and carryforward periods, tax planning strategies available, and the general and industry specific economic outlook. This realizability analysis is inherently subjective, as it requires management to forecast changes in the mortgage market, as well as the related impact on mortgage insurance, and the competitive and general economic environment in future periods. Changes in the estimate of deferred tax asset realizability, if applicable, are included in income tax expense on the consolidated statements of comprehensive income. ASC No. 740 provides a recognition threshold and measurement attribute for the financial statement recognition and measurement of a tax position taken or expected to be taken in a tax return. In accordance with ASC No. 740, before a tax benefit can be recognized, a tax position is evaluated using a threshold that it is more likely than not that the tax position will be sustained upon examination. When evaluating the more-likely-than-not recognition threshold, ASC No. 740 provides that a company should presume the tax position will be examined by the appropriate taxing authority that has full knowledge of all relevant information. If the tax position meets the more-likely-than-not recognition threshold, it is initially and subsequently measured as the largest amount of benefit that is greater than 50% likely of being realized upon ultimate settlement. As described in Note 12, we purchase non-interest-bearing United States Mortgage Guaranty Tax and Loss Bonds ("T&L Bonds") issued by the Treasury Department. These assets are carried at cost and are reported as prepaid federal income tax on the consolidated balance sheets. It is our policy to classify interest and penalties related to unrecognized tax benefits as income tax expense.
Earnings per Share	Earnings per Share Basic earnings per common share amounts are calculated based on income available to common stockholders and the weighted average number of common shares outstanding during the reporting period. Diluted earnings per common share amounts are calculated based on income available to common stockholders and the weighted average number of common and potential common shares outstanding during the reporting period. Potential common shares, composed of the incremental common shares issuable upon vesting of unvested common shares, are included in the earnings per share calculation to the extent that they are dilutive.
Recently Issued Accounting Standards	Recently Issued Accounting Standards In May 2014, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") ASU 2014-09, Revenue from Contracts with Customers (Topic 606). This update is intended to provide a consistent approach in recognizing revenue. In accordance with the new standard, recognition of revenue occurs when a customer obtains control of promised goods or services in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In addition, the new standard requires that reporting companies disclose the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. In July 2015, the FASB delayed the effective date for this update to interim and annual periods beginning after December 15, 2017. In December 2016, the FASB clarified that all contracts that are within the scope of Topic 944, Financial Services-Insurance, are excluded from the scope of ASU 2014-09. Accordingly, this update will not impact the recognition of revenue related to insurance premiums or investments, which represent a significant portion of our total revenues. The adoption of this ASU is not expected to have a material effect on the Company's consolidated operating results or financial position. In May 2015, the FASB issued ASU 2015-09, Disclosures about Short-Duration Contracts (Topic 944). The amendments in this update require insurance entities to disclose certain information about the liability for unpaid claims and claim adjustment expenses. The additional information required is focused on improvements in disclosures regarding insurance liabilities, including the nature, amount, timing, and uncertainty of cash flows related to those liabilities and the effect of those cash flows on the statement of comprehensive income. The disclosures required by this update are included in Note 6. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842). This update will require organizations that lease assets to recognize on the balance sheet the assets and liabilities for the rights and obligations created by those leases. The new guidance will also require additional disclosures about the amount, timing and uncertainty of cash flows arising from leases. The provisions of this update are effective for annual and interim periods beginning after December 15, 2018. The Company expects a gross-up of its consolidated balance sheets as a result of recognizing lease liabilities and right of use assets. The Company is still evaluating the impact the adoption of this ASU will have on the consolidated financial statements. In March 2016, the FASB issued ASU 2016-09, Improvements to Employee Share-Based Payment Accounting (Topic 718). This update is intended to simplify several aspects of the accounting for share-based payment award transactions, including the income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. The new guidance requires all excess tax benefits and tax deficiencies to be recognized as income tax expense or benefit in the income statement and treated as discrete items in the reporting period. In addition, excess tax benefits are required to be classified along with other income tax cash flows as an operating activity. Further, the new guidance allows for a policy election to account for forfeitures as they occur rather than on an estimated basis. The Company adopted this ASU on January 1, 2017 and recorded a charge of $0.1 million to retained earnings as of that date representing a cumulative-effect adjustment associated with our election to recognize forfeitures as they occur. The classification of excess tax benefits and tax deficiencies as income tax benefit or expense may result in net income volatility in reporting periods subsequent to 2016. Through December 31, 2016, excess tax benefits have been recognized in additional paid-in-capital. The amount of excess tax benefits or tax deficiencies in future periods will vary based on the market value of the Company’s common stock at the vesting dates of nonvested common share and nonvested common share units. In June 2016, the FASB issued ASU 2016-13, Measurement of Credit Losses on Financial Instruments (Topic 326). This update is intended to provide financial statement users with more information about the expected credit losses on financial instruments and other commitments to extend credit held by a reporting entity at each reporting date. The amendments in this ASU replace the incurred loss impairment methodology in current GAAP with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. The new guidance requires financial assets measured at amortized cost to be presented at the net amount expected to be collected through the use of an allowance for credit losses. Credit losses relating to available-for-sale debt securities will also be recorded through an allowance rather than as a write-down of the amortized cost of the securities. The provisions of this update are effective for annual and interim periods beginning after December 15, 2019. While the Company is still evaluating this ASU, we do not expect it to impact our accounting for insurance losses and loss adjustment expenses ("LAE") as these items are not within the scope of this ASU.