Employers (EIG) 10-Q 26 Jul 18 2018 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2018	Jul. 19, 2018
Document and Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2018
Entity Registrant Name	Employers Holdings, Inc.
Entity Central Index Key	1,379,041
Current Fiscal Year End Date	--12-31
Entity Well Know Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock Shares Outstanding		32,759,375
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q2

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Investments:
Fixed maturity securities at fair value (amortized cost $2,418.0 at June 30, 2018 and $2,421.0 at December 31, 2017)	$ 2,401,200	$ 2,463,400
Equity securities at fair value (cost $113.3 at March 31, 2018)	197,700
Equity securities, AFS, at fair value (cost $116.7 at December 31, 2017)		210,300
Equity securities at cost	6,400	0
Short-term investments at fair value (amortized cost $4.0 at December 31, 2017)	0	4,000
Total investments	2,605,300	2,677,700
Cash and cash equivalents	146,300	73,300
Restricted cash and cash equivalents	1,000	1,000
Accrued investment income	18,600	19,600
Premiums receivable (less bad debt allowance of $7.5 at June 30, 2018 and $10.0 at December 31, 2017)	355,600	326,700
Reinsurance recoverable for:
Paid losses	7,600	7,200
Unpaid losses	512,500	537,000
Deferred policy acquisition costs	51,700	45,800
Deferred income taxes, net	24,400	28,700
Property and equipment, net	20,300	13,900
Intangible assets, net	7,800	7,900
Goodwill	36,200	36,200
Contingent commission receivable—LPT Agreement	32,000	31,400
Other assets	49,200	33,700
Total assets	3,868,500	3,840,100
Claims and policy liabilities:
Unpaid losses and loss adjustment expenses	2,227,900	2,266,100
Unearned premiums	360,200	318,300
Total claims and policy liabilities	2,588,100	2,584,400
Commissions and premium taxes payable	58,900	55,300
Accounts payable and accrued expenses	23,400	23,700
Deferred reinsurance gain—LPT Agreement	154,700	163,600
Notes payable	20,000	20,000
Other liabilities	66,900	45,400
Total liabilities	2,912,000	2,892,400
Commitments and contingencies
Stockholders’ equity:
Common stock, $0.01 par value; 150,000,000 shares authorized; 56,866,727 and 56,695,174 shares issued and 32,759,575 and 32,597,819 shares outstanding at June 30, 2018 and December 31, 2017, respectively	600	600
Preferred stock, $0.01 par value; 25,000,000 shares authorized; none issued	0	0
Additional paid-in capital	382,400	381,200
Retained earnings	970,800	842,200
Accumulated other comprehensive (loss) income, net of tax	(13,300)	107,400
Treasury stock, at cost (24,107,152 shares at June 30, 2018 and 24,097,355 shares at December 31, 2017)	(384,000)	(383,700)
Total liabilities and stockholders’ equity	956,500	947,700
Total liabilities and stockholders’ equity	$ 3,868,500	$ 3,840,100

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Available for sale:
Amortized cost	$ 2,418,000	$ 2,541,700
Equity securities at fair value, cost	113,500
Available for sale, short-term investments, at amortized cost	0	4,000
Premiums receivable, bad debt allowance	7,500	10,000
Reinsurance Recoverables on Unpaid Losses, Allowance	$ 0	$ 0
Stockholders' equity
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	150,000,000	150,000,000
Common stock, shares issued (in shares)	56,866,727	56,695,174
Common stock, shares outstanding (in shares)	32,759,575	32,597,819
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	25,000,000	25,000,000
Preferred stock, shares issued (in shares)	0	0
Treasury stock, at cost (in shares)	24,107,152	24,097,355
Debt Securities [Member]
Available for sale:
Amortized cost	$ 2,418,000	$ 2,421,000
Equity Securities [Member]
Available for sale:
Amortized cost		116,700
Short-term Investments [Member]
Available for sale:
Amortized cost		$ 4,000

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues
Net premiums earned	$ 178,000	$ 171,700	$ 354,600	$ 347,100
Net investment income	20,300	18,200	39,700	36,900
Net realized and unrealized (losses) gains on investments	5,700	1,100	(2,400)	3,300
Net realized (losses) gains on investments	5,700	1,100		3,300
Gain on redemption of notes payable	0	2,100	0	2,100
Other income	100	100	100	100
Total revenues	204,100	193,200	392,000	389,500
Expenses
Losses and loss adjustment expenses	87,800	106,100	183,200	215,000
Commission expense	24,500	21,500	48,200	43,000
Underwriting and other operating expenses	40,100	32,600	79,200	68,600
Interest and financing expenses	400	400	700	800
Total expenses	152,800	160,600	311,300	327,400
Net income before income taxes	51,300	32,600	80,700	62,100
Income tax expense	8,800	7,800	12,600	14,100
Net income	42,500	24,800	68,100	48,000
Comprehensive income
Unrealized AFS investment (losses) gains arising during the period (net of taxes of $(3.0) and $4.5 for the three months ended June 30, 2018 and 2017, respectively, and $(12.6) and $9.7 for the six months ended June 30, 2018 and 2017, respectively)	(11,300)	8,400	(47,100)	17,900
Reclassification adjustment for realized AFS investment losses (gains) in net income (net of taxes of $(0.4) for the three months ended June 30, 2017, and $0.1 and $(1.2) for the six months ended June 30, 2018 and 2017, respectively)	0	(700)	400	(2,100)
Other comprehensive (loss) income, net of tax	(11,300)	7,700	(46,700)	15,800
Total comprehensive income	31,200	32,500	21,400	63,800
Net realized and unrealized gains (losses) on investments
Net realized and unrealized gains (losses) on investments before impairments	5,700	1,100	(400)	3,500
Other than temporary impairment recognized in earnings	0	0	(2,000)	(200)
Net realized and unrealized (losses) gains on investments	5,700	1,100	$ (2,400)	3,300
Net realized (losses) gains on investments	$ 5,700	$ 1,100		$ 3,300
Earnings per common share (Note 12):
Basic	$ 1.29	$ 0.76	$ 2.07	$ 1.48
Diluted	1.28	0.75	2.05	1.46
Cash dividends declared per common share and eligible RSUs and PSUs	$ 0.20	$ 0.15	$ 0.40	$ 0.30

Conolidated Statements of Compr

Conolidated Statements of Comprehensive Income (Parentheticals) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement Parenthetical [Abstract]
Other comprehensive income (loss), unrealized holding gain (loss) on securities arising during period, tax	$ (3,000)	$ 4,500	$ (12,600)	$ 9,700
Other comprehensive income (loss), reclassification adjustment for sale of securities included in net income, tax	$ 0	$ 400	$ (100)	$ 1,200

Consolidated Statements of Stoc

Consolidated Statements of Stockholders Equity Statement - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income, Net	Treasury Stock [Member]
Stockholders' equity, shares at Dec. 31, 2016		56,226,277
Stockholders' equity, value at Dec. 31, 2016	$ 840,600	$ 600	$ 372,000	$ 777,200	$ 74,500	$ (383,700)
Stock-based obligations, shares		0
Stock-based obligations, value	$ 3,200	$ 0	3,200	0	0	0
Stock-options exercised, shares	167,026	167,026
Stock-options exercised, value	$ 3,300	$ 0	3,300	0	0	0
Vesting of RSUs and PSUs, net of shares withheld to satisfy minimum tax withholding, shares		117,049
Vesting of RSUs and PSUs, net of shares withheld to satisfy minimum tax withholding, value	(1,900)	$ 0	(1,900)	0	0	0
Dividends declared, shares		0
Dividends declared, value	(9,800)	$ 0	0	(9,800)	0	0
Net income	48,000	0	0	48,000	0	0
Change in net unrealized gains in investments, net of tax	15,800	$ 0	0	0	15,800	0
Stockholders' equity, shares at Jun. 30, 2017		56,510,352
Stockholders' equity, value at Jun. 30, 2017	899,200	$ 600	376,600	815,400	90,300	(383,700)
Stockholders' equity, shares at Dec. 31, 2016		56,226,277
Stockholders' equity, value at Dec. 31, 2016	$ 840,600	$ 600	372,000	777,200	74,500	(383,700)
Stock-options exercised, shares	307,076
Stockholders' equity, shares at Dec. 31, 2017	56,695,174	56,695,174
Stockholders' equity, value at Dec. 31, 2017	$ 947,700	$ 600	381,200	842,200	107,400	(383,700)
Stock-based obligations, shares		0
Stock-based obligations, value	$ 3,900	$ 0	3,900	0	0	0
Stock-options exercised, shares	13,800	13,800
Stock-options exercised, value	$ 200	$ 0	200	0	0	0
Vesting of RSUs and PSUs, net of shares withheld to satisfy minimum tax withholding, shares		157,753
Vesting of RSUs and PSUs, net of shares withheld to satisfy minimum tax withholding, value	(2,900)	$ 0	(2,900)	0	0	0
Acquisition of common stock, shares		0
Acquisition of common stock, value	(300)	$ 0	0	0	0	(300)
Dividends declared, shares		0
Dividends declared, value	(13,300)	$ 0	0	(13,300)	0	0
Net income	68,100	0	0	68,100	0	0
Change in net unrealized gains in investments, net of tax	$ (46,700)	$ 0	0	0	(46,700)	0
Stockholders' equity, shares at Jun. 30, 2018	56,866,727	56,866,727
Stockholders' equity, value at Jun. 30, 2018	$ 956,500	$ 600	382,400	970,800	(13,300)	(384,000)
Reclassification adjustment for adoption of ASU | Accounting Standards Update 2016-01 [Member]	$ 0	$ 0	$ 0	$ 74,000	$ (74,000)	$ 0

Conslidated Stockholders Equity

Conslidated Stockholders Equity (Parentheticals) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Statement of Stockholders' Equity Parenthetical [Abstract]
Change in net unrealized (losses) gains on investments, net of tax	$ (12.5)	$ 8.5

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Operating activities
Net income	$ 68,100	$ 48,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	3,800	4,200
Stock-based compensation	3,800	3,100
Amortization of premium on investments, net	4,400	7,500
Allowance for doubtful accounts	(2,500)	100
Deferred income tax (benefit) expense	16,800	6,000
Net realized and unrealized losses (gains) on investments	2,400	(3,300)
Gain on redemption of notes payable	0	(2,100)
Change in operating assets and liabilities:
Premiums receivable	(26,500)	(28,500)
Reinsurance recoverable on paid and unpaid losses	24,100	20,500
Current federal income taxes	(7,100)	(6,900)
Unpaid losses and loss adjustment expenses	38,200	16,100
Unearned premiums	41,900	30,800
Accounts payable, accrued expenses and other liabilities	4,000	(7,100)
Deferred reinsurance gain—LPT Agreement	(8,900)	(6,000)
Other	100	(7,600)
Net cash provided by operating activities	86,200	42,600
Investing activities
Purchases of fixed maturity securities	(358,100)	(202,100)
Purchases of equity securities	(19,900)	(10,700)
Purchases of short-term investments	(34,900)	(8,100)
Proceeds from sale of fixed maturity securities	168,400	43,000
Proceeds from sale of equity securities	24,000	11,400
Proceeds from maturities and redemptions of fixed maturity securities	187,700	96,800
Proceeds from maturities of short-term investments	38,900	18,600
Net change in unsettled investment purchases and sales	7,200	5,000
Capital expenditures and other	(10,100)	(5,900)
Net cash provided by (used in) investing activities	3,200	(52,000)
Financing activities
Acquisition of common stock	(300)	0
Cash transactions related to stock-based compensation	(2,700)	1,400
Dividends paid to stockholders	(13,300)	(9,800)
Redemption of notes payable	0	(9,900)
Payments on capital leases	100	100
Net cash used in financing activities	(16,400)	(18,400)
Net increase (decrease) in cash, cash equivalents and restricted cash	73,000	(27,800)
Cash, cash equivalents, restricted cash and restricted cash equivalents at the beginning of the period	74,300	70,800
Cash, cash equivalents, restricted cash and restricted cash equivalents at the end of the period	147,300	43,000
Total cash, cash equivalents, restricted cash	$ 74,300	$ 70,800

Basis of Presentation

Basis of Presentation	6 Months Ended
	Jun. 30, 2018
Basis of Presentation [Abstract]
Basis of Presentation	Basis of Presentation and Summary of Operations Employers Holdings, Inc. (EHI) is a Nevada holding company. Through its wholly owned insurance subsidiaries, Employers Insurance Company of Nevada (EICN), Employers Compensation Insurance Company (ECIC), Employers Preferred Insurance Company (EPIC), and Employers Assurance Company (EAC), EHI is engaged in the commercial property and casualty insurance industry, specializing in workers' compensation products and services. Unless otherwise indicated, all references to the “Company” refer to EHI, together with its subsidiaries. In 1999, the Nevada State Industrial Insurance System (the Fund) entered into a retroactive 100% quota share reinsurance agreement (the LPT Agreement) through a loss portfolio transfer transaction with third party reinsurers. The LPT Agreement commenced on June 30, 1999 and will remain in effect until all claims under the covered policies have closed, the LPT Agreement is commuted or terminated, upon the mutual agreement of the parties, or the reinsurers' aggregate maximum limit of liability is exhausted, whichever occurs first. The LPT Agreement does not provide for any additional termination terms. On January 1, 2000, EICN assumed all of the assets, liabilities and operations of the Fund, including the Fund's rights and obligations associated with the LPT Agreement (See Note 8 ). The Company accounts for the LPT Agreement as retroactive reinsurance. Upon entry into the LPT Agreement, an initial deferred reinsurance gain (the Deferred Gain) was recorded as a liability on the Company’s Consolidated Balance Sheets. The Company is entitled to receive a contingent profit commission under the LPT Agreement. The contingent profit commission is estimated based on both actual paid results to date and projections of expected paid losses under the LPT Agreement and is recorded as an asset on the Company's Consolidated Balance Sheets. The accompanying consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X of the Securities Exchange Act of 1934, as amended. Accordingly, they do not include all of the information and notes required by GAAP for complete financial statements. In the opinion of management, all adjustments (consisting of normal, recurring adjustments) necessary for a fair presentation of the Company’s consolidated financial position and results of operations for the periods presented have been included. The results of operations for an interim period are not necessarily indicative of the results for an entire year. These financial statements have been prepared consistent with the accounting policies described in the Company’s Form 10-K for the year ended December 31, 2017 (Annual Report). The Company operates as a single operating segment, workers' compensation insurance, through its wholly owned subsidiaries. The Company considers an operating segment to be any component of its business whose operating results are regularly reviewed by the Company’s chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance based on discrete financial information. Use of Estimates The preparation of the consolidated financial statements in conformity 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 consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. As a result, actual results could differ from these estimates. The most significant areas that require management judgment are the estimate of unpaid losses and loss adjustment expenses (LAE), evaluation of reinsurance recoverables, recognition of premium revenue, recoverability of deferred income taxes, and valuation of investments. Reclassifications Certain prior period information has been reclassified to conform to the current period presentation. Pending Acquisition On August 11, 2017, the Company entered into, and on May 23, 2018, the Company amended, a stock purchase agreement (Purchase Agreement) with Partner Reinsurance Company of the U.S. (PRUS) with respect to the acquisition (Acquisition) of all of the outstanding shares of capital stock of PartnerRe Insurance Company of New York (PRNY). The purchase price is equal to the sum of: (i) the amount of statutory capital and surplus of PRNY at closing (which is currently estimated to be approximately $40.0 million ); and (ii) $5.8 million . The Company expects to fund the Acquisition with cash on hand. Pursuant to the Purchase Agreement, all liabilities and obligations of PRNY existing as of the closing date, whether known or unknown, will be indemnified by PRUS. In addition, PartnerRe Ltd., the parent company of PRUS, has provided the Company with a Guaranty that unconditionally, absolutely and irrevocably guarantees the full and prompt payment and performance by PRUS of all of its obligations, liabilities, and indemnities under the Purchase Agreement and the transactions contemplated thereby. The Company will not be acquiring any employees or ongoing business operations pursuant to the Acquisition. The Acquisition is subject to certain closing conditions, including, among other things, approval from the Department of Financial Services of the State of New York.

Changes in Estimates Level 1 (N

Changes in Estimates Level 1 (Notes)	6 Months Ended
	Jun. 30, 2018
Changes in Estimates [Abstract]
Change in Estimates	Change in Estimates The Company reduced its estimated loss and LAE reserves ceded under the Loss Portfolio Transfer Agreement (LPT Reserve Adjustment) as a result of the determination that an adjustment was necessary to reflect observed favorable paid loss trends during the second quarter of 2018 . The following table shows the financial statement impact related to the LPT Reserve Adjustment. Three Months Ended Six Months Ended June 30, 2018 June 30, 2018 (in millions, except per share data) LPT Reserve Adjustment $ (6.3 ) $ (6.3 ) Cumulative adjustment to the Deferred Gain (1) (2.2 ) (2.2 ) Net income impact from this change in estimate 2.2 2.2 Earnings per common share impact from this change in estimate: Basic and Diluted 0.07 0.07 (1) The cumulative adjustment to the Deferred reinsurance gain–LPT Agreement (Deferred Gain) was also recognized in losses and LAE incurred in the Company's Consolidated Statement of Comprehensive Income, so that the Deferred Gain reflects the balance that would have existed had the revised loss and LAE reserves been recognized at the inception of the LPT Agreement. The Company increased its estimate of Contingent commission receivable – LPT Agreement (LPT Contingent Commission Adjustment) as a result of the determination that an adjustment was necessary to reflect observed favorable paid loss trends during the second quarter of 2018 . The following table shows the financial statement impact related to the LPT Contingent Commission Adjustment. Three Months Ended Six Months Ended June 30, 2018 June 30, 2018 (in millions, except per share data) LPT Contingent Commission Adjustment $ 0.5 $ 0.5 Net income impact from this change in estimate 0.5 0.5 Earnings per common share impact from this change in estimate: Basic and Diluted 0.02 0.02

New Accounting Standards Level

New Accounting Standards Level 1 (Notes)	6 Months Ended
	Jun. 30, 2018
New Accounting Standards [Abstract]
New Accounting Standards	New Accounting Standards Recently Issued Accounting Standards In February 2016, the FASB issued ASU Number 2016-02, Leases (Topic 842). This update provides guidance on a new lease model that includes the recognition of assets and liabilities arising from lease transactions on the balance sheet. Additionally, the update provides clarity on the definition of a lease and the distinction between finance and operating leases. Furthermore, the update requires certain qualitative and quantitative disclosures pertaining to the amounts recorded in the financial statements. This update becomes effective for annual reporting periods, including interim periods within those annual periods, beginning after December 15, 2018 and early adoption is permitted. The Company has determined that the impact of this new standard will be equal to the present value of the Company's lease obligations under various non-cancellable operating lease contracts, which amounted to approximately $23.0 million at June 30, 2018 , and will be recognized as lease assets and liabilities on the Company's Balance Sheets upon adoption. Recently Adopted Accounting Standards In March 2018, the FASB issued ASU Number 2018-05, Income Taxes (Topic 740) . This update provides guidance regarding the application of ASC Topic 740 for the income tax effects of the Tax Cuts and Jobs Act. This update allowed companies to report provisional amounts of the effects of the Tax Cuts and Jobs Act in their financial statements in the first reporting period they are able to determine a reasonable estimate and any adjustments to provisional amounts should be included in income from continuing operations as an adjustment to tax expense or benefit in the reporting period the amounts are determined. The Company adopted this update in the fourth quarter of 2017 and included an estimate of the income tax effects in its financial statements for the year ended December 31, 2017. The Company does not expect the amounts of any future income tax adjustments related to the effects of the Tax Cuts and Jobs Act to be material. In January 2016, the FASB issued ASU Number 2016-01, Financial Instruments - Overall (Subtopic 825-10) . This update replaces the guidance to classify equity securities with readily determinable fair values into different categories (trading or available-for-sale) and requires those equity securities to be measured at fair value with changes in fair value recognized through net income. Additionally, this update eliminates the disclosure of the method and significant assumptions used to estimate the fair value of financial instruments measured at amortized cost. It requires financial instruments to be measured at fair value using the exit price notion. Furthermore, this update clarifies that an evaluation of deferred tax assets related to available-for-sale securities is needed, in combination with an evaluation of other deferred tax assets, to determine if a valuation allowance is required. This update did not apply to the Company’s investment in Federal Home Loan Bank (FHLB) stock. Rather, it specified that FHLB stock shall be carried at cost and evaluated periodically for impairment; furthermore, it specified that, beginning January 1, 2018, FHLB stock shall not be shown with securities accounted for under ASC 321, which provides detailed guidance on, among other things, accounting and reporting of investments in equity securities that have readily determinable fair values. As a result, the Company’s investment in FHLB stock is presented within Equity securities at cost on the Company's Consolidated Balance Sheet at March 31, 2018. In all periods prior to January 1, 2018, the Company's investment in FHLB stock is presented within Equity securities at fair value on the Company's Consolidated Balance Sheets. This update became effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. The Company adopted this update effective January 1, 2018. Adoption of this accounting standard resulted in a $74.0 million reclassification adjustment, net of tax, from accumulated other comprehensive income to retained earnings.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	6 Months Ended
	Jun. 30, 2018
Fair Value of Financial Instruments [Abstract]
Fair Value of Financial Instruments	Fair Value of Financial Instruments The carrying value and the estimated fair value of the Company’s financial instruments at fair value were as follows: June 30, 2018 December 31, 2017 Carrying Value Estimated Fair Value Carrying Value Estimated Fair Value (in millions) Financial assets Total investments at fair value $ 2,598.9 $ 2,598.9 $ 2,677.7 $ 2,677.7 Cash and cash equivalents 146.3 146.3 73.3 73.3 Restricted cash and cash equivalents 1.0 1.0 1.0 1.0 Financial liabilities Notes payable $ 20.0 $ 23.5 $ 20.0 $ 23.6 Assets and liabilities recorded at fair value on the Company's Consolidated Balance Sheets are categorized based upon the levels of judgment associated with the inputs used to measure their fair value. Level inputs are defined as follows: • Level 1 - Inputs are unadjusted quoted market prices for identical assets or liabilities in active markets at the measurement date. • Level 2 - Inputs other than Level 1 prices that are observable for similar assets or liabilities through corroboration with market data at the measurement date. • Level 3 - Inputs that are unobservable that reflect management's best estimate of what willing market participants would use in pricing the assets or liabilities at the measurement date. The Company uses third party pricing services to assist it with its investment accounting function. The ultimate pricing source varies depending on the investment security and pricing service used, but investment securities valued on the basis of observable inputs (Levels 1 and 2) are generally assigned values on the basis of actual transactions. Securities valued on the basis of pricing models with significant unobservable inputs or non-binding broker quotes are classified as Level 3. The Company performs quarterly analyses on the prices it receives from third parties to determine whether the prices are reasonable estimates of fair value, including confirming the fair values of these securities through observable market prices using an alternative pricing source, as it is ultimately management’s responsibility to ensure that the fair values reflected in the Company’s consolidated financial statements are appropriate. If differences are noted in these analyses, the Company may obtain additional information from other pricing services to validate the quoted price. The Company bases all of its estimates of fair value for assets on the bid prices, when available, as they represent what a third-party market participant would be willing to pay in an arm's length transaction. For securities not actively traded, third party pricing services may use quoted market prices of similar instruments or discounted cash flow analyses, incorporating inputs that are currently observable in the markets for similar securities. Inputs that are often used in the valuation methodologies include, but are not limited to, broker quotes, benchmark yields, credit spreads, default rates, and prepayment speed assumptions. There were no material adjustments made to the prices obtained from third party pricing services as of June 30, 2018 and December 31, 2017 . These methods of valuation only produce an estimate of fair value if there is objectively verifiable information to produce a valuation. When objectively verifiable information is not available, the Company produces an estimate of fair value using some of the same methodologies, making assumptions for market-based inputs that are unavailable. The Company's estimates of fair value for its notes payable are based on a combination of the variable interest rates for notes with similar durations to discount the projection of future payments on notes payable. The fair value measurements for notes payable have been determined to be Level 2 at each of the periods presented. Each of the Company's insurance operating subsidiaries is a member of the FHLB of San Francisco. Members are required to purchase stock in FHLB in addition to maintaining collateral deposits that back any funds advanced. The Company's investment in FHLB stock is recorded at cost, as purchases and sales of these securities are at par value with the issuer. FHLB stock is considered a restricted security and is periodically evaluated by the Company for impairment based on the ultimate recovery of par value. The following table presents the Company's investments at fair value and the corresponding fair value measurements. June 30, 2018 December 31, 2017 Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 (in millions) Fixed maturity securities: U.S. Treasuries $ — $ 119.4 $ — $ — $ 137.0 $ — U.S. Agencies — 11.5 — — 11.8 — States and municipalities — 568.7 — — 642.5 — Corporate securities — 1,079.5 — — 1,118.0 — Residential mortgage-backed securities — 433.1 — — 389.3 — Commercial mortgage-backed securities — 104.0 — — 106.0 — Asset-backed securities — 67.3 — — 58.8 — Other securities — 17.7 — — — — Total fixed maturity securities $ — $ 2,401.2 $ — $ — $ 2,463.4 $ — Equity securities at fair value: Industrial and miscellaneous $ 172.6 $ — $ — $ 181.7 $ — $ — Non-redeemable preferred stock (FHLB) — — — — — 4.7 Other 25.1 — — 23.9 — — Total equity securities at fair value 197.7 — — 205.6 — 4.7 Short-term investments — — — — 4.0 — Total investments at fair value $ 197.7 $ 2,401.2 $ — $ 205.6 $ 2,467.4 $ 4.7 Certain cash equivalents, principally money market securities, are measured at fair value using the net asset value (NAV) per share. The following table presents cash equivalents at NAV and total cash and cash equivalents carried at fair value on the Company's Consolidated Balance Sheets. June 30, 2018 December 31, 2017 (in millions) Cash and cash equivalents at fair value $ 61.3 $ 34.3 Cash equivalents measured at NAV, which approximates fair value 85.0 39.0 Total cash and cash equivalents $ 146.3 $ 73.3 The following table provides a reconciliation of the beginning and ending balances of investments that are recorded at fair value and are measured using Level 3 inputs for the six months ended June 30, 2018 and 2017 . Level 3 Securities 2018 2017 (in millions) Beginning balance, January 1 $ 4.7 $ 11.9 Transfers out of Level 3 (1) (4.7 ) (7.0 ) Purchases and sales, net — (0.2 ) Ending balance, June 30 $ — $ 4.7 (1) The transfer during the six months ended June 30, 2018 was the result of adoption of ASU 2016-01, which specified that FHLB stock shall be carried at cost and is no longer measured at fair value. Transfers during the six months ended June 30, 2017 were from Level 3 to Level 2 as observable market data became available for these securities.

Investments

Investments	6 Months Ended
	Jun. 30, 2018
Investments [Abstract]
Investments	Investments The Company's investments in fixed maturity securities, equity securities at fair value (prior to 2018), and short-term investments are classified as available-for-sale (AFS) that are reported at fair value with unrealized gains and losses excluded from earnings and reported as a separate component of stockholders' equity, net of deferred taxes, in Accumulated other comprehensive (loss) income (AOCI) on the Company’s Consolidated Balance Sheets. Beginning in 2018, with the adoption of ASU 2016-01, the Company's investments in equity securities at fair value are no longer classified as AFS and changes in fair value are included in Net realized and unrealized (losses) gains on investments on the Company's Consolidated Statements of Comprehensive Income. Effective January 1, 2018, the Company's investment in FHLB stock is presented within Equity securities at cost on the Company's Consolidated Balance Sheets. Other securities within fixed maturity securities consist of bank loans, which are classified as AFS and are reported at fair value. The cost or amortized cost, gross unrealized gains, gross unrealized losses, and estimated fair value of the Company’s AFS investments were as follows: Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value (in millions) At June 30, 2018 Fixed maturity securities U.S. Treasuries $ 120.4 $ 0.9 $ (1.9 ) $ 119.4 U.S. Agencies 11.3 0.3 (0.1 ) 11.5 States and municipalities 555.0 14.9 (1.2 ) 568.7 Corporate securities 1,095.9 6.5 (22.9 ) 1,079.5 Residential mortgage-backed securities 442.9 2.0 (11.8 ) 433.1 Commercial mortgage-backed securities 107.1 — (3.1 ) 104.0 Asset-backed securities 67.6 0.2 (0.5 ) 67.3 Other securities 17.8 — (0.1 ) 17.7 Total fixed maturity securities 2,418.0 24.8 (41.6 ) 2,401.2 Total AFS investments $ 2,418.0 $ 24.8 $ (41.6 ) $ 2,401.2 At December 31, 2017 Fixed maturity securities U.S. Treasuries $ 135.8 $ 2.0 $ (0.8 ) $ 137.0 U.S. Agencies 11.3 0.5 — 11.8 States and municipalities 617.0 25.5 — 642.5 Corporate securities 1,103.4 18.0 (3.4 ) 1,118.0 Residential mortgage-backed securities 388.3 3.6 (2.6 ) 389.3 Commercial mortgage-backed securities 106.5 0.4 (0.9 ) 106.0 Asset-backed securities 58.7 0.3 (0.2 ) 58.8 Total fixed maturity securities 2,421.0 50.3 (7.9 ) 2,463.4 Equity securities at fair value Industrial and miscellaneous 100.8 81.5 (0.6 ) 181.7 Non-redeemable preferred stock (FHLB) 4.7 — — 4.7 Other 11.2 12.7 — 23.9 Total equity securities at fair value 116.7 94.2 (0.6 ) 210.3 Short-term investments 4.0 — — 4.0 Total AFS investments $ 2,541.7 $ 144.5 $ (8.5 ) $ 2,677.7 The cost and estimated fair value of the Company’s equity securities recorded at fair value at June 30, 2018 were as follows: Cost Estimated Fair Value (in millions) At June 30, 2018 Equity securities at fair value Industrial and miscellaneous $ 99.4 $ 172.6 Other 14.1 25.1 Total equity securities at fair value $ 113.5 $ 197.7 The amortized cost and estimated fair value of the Company's fixed maturity securities at June 30, 2018 , by contractual maturity, are shown below. Expected maturities differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. Amortized Cost Estimated Fair Value (in millions) Due in one year or less $ 177.8 $ 178.3 Due after one year through five years 761.7 763.6 Due after five years through ten years 730.0 720.6 Due after ten years 130.9 134.3 Mortgage and asset-backed securities 617.6 604.4 Total $ 2,418.0 $ 2,401.2 The following is a summary of AFS investments that have been in a continuous unrealized loss position for less than 12 months and those that have been in a continuous unrealized loss position for 12 months or greater as of June 30, 2018 and December 31, 2017 . June 30, 2018 December 31, 2017 Estimated Fair Value Gross Number of Issues Estimated Fair Value Gross Number of Issues (in millions, except number of issues data) Less than 12 months: Fixed maturity securities U.S. Treasuries $ 82.0 $ (1.6 ) 27 $ 86.0 $ (0.5 ) 28 U.S. Agencies 3.7 (0.1 ) 2 — — — States and municipalities 84.0 (1.2 ) 24 — — — Corporate securities 811.5 (21.0 ) 265 307.6 (2.3 ) 113 Residential mortgage-backed securities 310.0 (8.1 ) 93 165.0 (0.8 ) 45 Commercial mortgage-backed securities 75.4 (2.0 ) 34 41.8 (0.2 ) 19 Asset-backed securities 53.1 (0.5 ) 37 29.3 (0.2 ) 25 Other securities 16.1 (0.1 ) 23 — — — Total less than 12 months $ 1,435.8 $ (34.6 ) 505 $ 629.7 $ (4.0 ) 230 12 months or greater: Fixed maturity securities U.S. Treasuries $ 17.7 $ (0.3 ) 9 $ 23.4 $ (0.3 ) 10 Corporate securities 36.1 (1.9 ) 15 53.2 (1.1 ) 17 Residential mortgage-backed securities 69.7 (3.7 ) 32 77.1 (1.8 ) 32 Commercial mortgage-backed securities 20.2 (1.1 ) 8 25.1 (0.7 ) 8 Total 12 months or greater $ 143.7 $ (7.0 ) 64 $ 178.8 $ (3.9 ) 67 At December 31, 2017 , the Company also had $0.6 million of gross unrealized losses on 24 equity securities that were in a continuous loss position for less than 12 months. The Company recognized impairments on fixed maturity securities of $2.0 million (consisting of 57 securities) during the six months ended June 30, 2018 as a result of the Company's intent to sell these securities. There were no other-than-temporary impairments on fixed maturity securities recognized during the six months ended June 30, 2017 . The Company determined that the remaining unrealized losses on fixed maturity securities for the six months ended June 30, 2018 were primarily the result of changes in prevailing interest rates and not the credit quality of the issuers. The fixed maturity securities whose total fair value was less than amortized cost were not determined to be other-than-temporarily impaired given the lack of severity and duration of the impairment, the credit quality of the issuers, the Company’s intent to not sell the securities, and a determination that it is not more likely than not that the Company will be required to sell the securities at an amount less than their amortized cost. The adoption of ASU 2016-01 removed the impairment assessment for equity securities at fair value, and, beginning in 2018, changes in fair value are included in Net realized and unrealized (losses) gains on investments on the Company's Consolidated Statements of Comprehensive Income. Prior to the adoption of this standard, the Company recognized an impairment on equity securities of $0.2 million (consisting of one security) during the six months ended June 30, 2017 . The other-than-temporary impairment recognized during this period was the result of the severity and duration of the change in fair value of this security. Certain unrealized losses on equity securities during the six months ended June 30, 2017 were not considered to be other-than-temporary due to the financial condition and near-term prospects of the issuers, and the Company's intent to hold the securities until fair value recovers to above cost. Realized gains and losses on investments include the gain or loss on a security at the time of sale compared to its original or adjusted cost (equity securities) or amortized cost (fixed maturity securities). Realized losses on fixed maturity securities are also recognized when securities are written down as a result of an other-than-temporary impairment. Net realized gains on investments and the change in unrealized gains (losses) on the Company's investments recorded at fair value are determined on a specific-identification basis and were as follows: Gross Realized Gains Gross Realized Losses Change in Net Unrealized Gains (Losses) Changes in Fair Value Reflected in Earnings Changes in Fair Value Reflected in AOCI, before tax (in millions) Three Months Ended June 30, 2018 Fixed maturity securities $ 0.3 $ (0.3 ) $ (14.3 ) $ — $ (14.3 ) Equity securities 2.6 (0.4 ) 3.5 5.7 — Total investments $ 2.9 $ (0.7 ) $ (10.8 ) $ 5.7 $ (14.3 ) Six Months Ended June 30, 2018 Fixed maturity securities $ 2.1 $ (2.6 ) $ (59.2 ) $ (0.5 ) $ (59.2 ) Equity securities 8.1 (0.6 ) (9.4 ) (1.9 ) — Total investments $ 10.2 $ (3.2 ) $ (68.6 ) $ (2.4 ) $ (59.2 ) Three Months Ended June 30, 2017 Fixed maturity securities $ — $ — $ 12.5 $ — $ 12.5 Equity securities 1.1 — (0.7 ) 1.1 (0.7 ) Total investments $ 1.1 $ — $ 11.8 $ 1.1 $ 11.8 Six Months Ended June 30, 2017 Fixed maturity securities $ 0.5 $ (0.1 ) $ 18.9 $ 0.4 $ 18.9 Equity securities 3.1 (0.2 ) 5.4 2.9 5.4 Total investments $ 3.6 $ (0.3 ) $ 24.3 $ 3.3 $ 24.3 Net investment income was as follows: Three Months Ended Six Months Ended June 30, June 30, 2018 2017 2018 2017 (in millions) Fixed maturity securities $ 19.2 $ 17.3 $ 37.7 $ 35.0 Equity securities 1.7 1.7 3.3 3.5 Cash equivalents and restricted cash 0.3 0.1 0.5 0.2 Gross investment income 21.2 19.1 41.5 38.7 Investment expenses (0.9 ) (0.9 ) (1.8 ) (1.8 ) Net investment income $ 20.3 $ 18.2 $ 39.7 $ 36.9 The Company is required by various state laws and regulations to hold securities or letters of credit in depository accounts with certain states in which it does business. These laws and regulations govern not only the amount but also the types of securities that are eligible for deposit. As of June 30, 2018 and December 31, 2017 , securities having a fair value of $954.4 million and $1,009.7 million , respectively, were on deposit. Additionally, standby letters of credit from the FHLB were in place in lieu of $140.0 million of securities on deposit as of June 30, 2018 (See Note 9 ). Certain reinsurance contracts require the Company's funds to be held in trust for the benefit of the ceding reinsurer to secure the outstanding liabilities assumed by the Company. The fair value of fixed maturity securities and restricted cash and cash equivalents held in trust for the benefit of ceding reinsurers at June 30, 2018 and December 31, 2017 was $22.9 million and $24.5 million , respectively.

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2018
Income Taxes [Abstract]
Income Taxes	Income Taxes Income tax expense for interim periods is measured using an estimated effective tax rate for the annual period. The Company's effective tax rates were 17.2% and 15.6% for the three and six months ended June 30, 2018 , respectively, compared to 23.9% and 22.7% for the same periods of 2017 . Tax-advantaged investment income, Deferred Gain amortization, LPT Reserve Adjustments, LPT Contingent Commission Adjustments, and certain other adjustments reduced the Company's effective income tax rate below the U.S. statutory rates of 21% and 35% for periods in 2018 and 2017 , respectively.

Liability for Unpaid Losses and

Liability for Unpaid Losses and Loss Adjustment Expenses	6 Months Ended
	Jun. 30, 2018
Liability for Unpaid Losses and Loss Adjustment Expenses [Abstract]
Liability for Unpaid Losses and Loss Adjustment Expenses	Liability for Unpaid Losses and Loss Adjustment Expenses The following table represents a reconciliation of changes in the liability for unpaid losses and LAE. Three Months Ended Six Months Ended June 30, June 30, 2018 2017 2018 2017 (in millions) Unpaid losses and LAE at beginning of period $ 2,258.1 $ 2,298.2 $ 2,266.1 $ 2,301.0 Less reinsurance recoverable, excluding bad debt allowance, on unpaid losses and LAE 531.1 572.9 537.0 580.0 Net unpaid losses and LAE at beginning of period 1,727.0 1,725.3 1,729.1 1,721.0 Losses and LAE, net of reinsurance, incurred during the period related to: Current period 111.2 109.4 221.6 221.3 Prior periods (16.5 ) (0.3 ) (28.9 ) (0.3 ) Total net losses and LAE incurred during the period 94.7 109.1 192.7 221.0 Paid losses and LAE, net of reinsurance, related to: Current period 20.0 17.0 25.9 21.7 Prior periods 86.3 92.3 180.5 195.2 Total net paid losses and LAE during the period 106.3 109.3 206.4 216.9 Ending unpaid losses and LAE, net of reinsurance 1,715.4 1,725.1 1,715.4 1,725.1 Reinsurance recoverable, excluding bad debt allowance, on unpaid losses and LAE 512.5 559.8 512.5 559.8 Unpaid losses and LAE at end of period $ 2,227.9 $ 2,284.9 $ 2,227.9 $ 2,284.9 Total net losses and LAE included in the above table exclude amortization of the deferred reinsurance gain—LPT Agreement, LPT Reserve Adjustments, and LPT Contingent Commission Adjustments, which totaled $6.9 million and $3.1 million for the three months ended June 30, 2018 and 2017 , respectively, and $9.5 million and $6.0 million for the six months ended June 30, 2018 and 2017 , respectively (See Note 8 ). The change in incurred losses and LAE attributable to prior periods included $16.5 million and $28.5 million of favorable development on the Company's voluntary risk business for the three and six months ended June 30, 2018 , respectively, and $0.4 million of favorable development on the Company's assigned risk business for the six months ended June 30, 2018 .

LPT Agreement

LPT Agreement	6 Months Ended
	Jun. 30, 2018
LPT Agreement [Abstract]
LPT Agreement	LPT Agreement The Company is party to the LPT Agreement under which $1.5 billion in liabilities for losses and LAE related to claims incurred by the Fund prior to July 1, 1995 were reinsured for consideration of $775.0 million . The LPT Agreement provides coverage up to $2.0 billion . The Company records its estimate of contingent profit commission in the accompanying Consolidated Balance Sheets as Contingent commission receivable–LPT Agreement and a corresponding liability is recorded in the accompanying Consolidated Balance Sheets in Deferred reinsurance gain–LPT Agreement. The Deferred Gain is being amortized using the recovery method. Amortization is determined by the proportion of actual reinsurance recoveries to total estimated recoveries over the life of the LPT Agreement, except for the contingent profit commission, which is amortized through June 30, 2024, the date through which the Company is entitled to receive a contingent profit commission under the LPT Agreement. The amortization is recorded in losses and LAE incurred in the accompanying consolidated statements of comprehensive income. Any adjustments to the Deferred Gain are recorded in losses and LAE incurred in the accompanying consolidated statements of comprehensive income. The Company amortized $4.2 million and $3.1 million of the Deferred Gain for the three months ended June 30, 2018 and 2017 , respectively, and $6.8 million and $6.0 million for the six months ended June 30, 2018 and 2017 , respectively. Additionally, the Deferred Gain was further reduced by $2.2 million for the three and six months ended June 30, 2018 due to a favorable LPT Reserve Adjustment and by $0.5 million of amortization for the three and six months ended June 30, 2018 due to a favorable LPT Contingent Commission Adjustment (see Note 2 ). The remaining Deferred Gain was $154.7 million and $163.6 million as of June 30, 2018 and December 31, 2017 , respectively. The estimated remaining liabilities subject to the LPT Agreement were $420.3 million and $438.9 million as of June 30, 2018 and December 31, 2017 , respectively. Losses and LAE paid with respect to the LPT Agreement totaled $761.6 million and $749.3 million from inception through June 30, 2018 and December 31, 2017 , respectively.

Notes Payable Level 1 (Notes)

Notes Payable Level 1 (Notes)	6 Months Ended
	Jun. 30, 2018
Notes Payable [Abstract]
Debt Disclosure [Text Block]	Notes Payable and Other Financing Arrangements Notes payable is comprised of the following: June 30, 2018 December 31, 2017 (in millions) Dekania Surplus Note, due April 29, 2034 $ 10.0 $ 10.0 Alesco Surplus Note, due December 15, 2034 10.0 10.0 Total $ 20.0 $ 20.0 EPIC has a $10.0 million surplus note to Dekania CDO II, Ltd. issued as part of a pooled transaction. The note matures in 2034 and became callable by the Company in 2009 . The terms of the note provide for quarterly interest payments at a rate 425 basis points in excess of the 90-day LIBOR. Both the payment of interest and repayment of the principal under this note and the surplus note described in the following paragraph are subject to the prior approval of the Florida Department of Financial Services. EPIC has a $10.0 million surplus note to Alesco Preferred Funding V, LTD issued as part of a pooled transaction. The note matures in 2034 and became callable by the Company in 2009 . The terms of the note provide for quarterly interest payments at a rate 405 basis points in excess of the 90-day LIBOR. Other financing arrangements is comprised of the following: Each of the Company's insurance subsidiaries is a member of the FHLB. Membership allows the insurance subsidiaries access to collateralized advances, which may be used to support and enhance liquidity management. The amount of advances that may be taken is dependent on statutory admitted assets on a per company basis. Currently, none of the Company's insurance subsidiaries has advances outstanding under the FHLB facility. FHLB membership also allows the Company's insurance subsidiaries access to standby letters of credit. On March 9, 2018, ECIC, EPIC, and EAC entered into standby Letter of Credit Reimbursement Agreements (Letter of Credit Agreements) with the FHLB. The Letter of Credit Agreements are between FHLB and each of EAC, in the amount of $40.0 million , ECIC, in the amount of $50.0 million , and EPIC, in the amount of $50.0 million . The Letter of Credit Agreements became effective March 9, 2018 and expire March 31, 2019; however, the Letter of Credit Agreements will remain evergreen with automatic one-year extensions unless the FHLB notifies the beneficiary at least 60 days prior to the then applicable expiration date of its election not to renew. The Letter of Credit Agreements may only be used to satisfy, in whole or in part, insurance deposit requirements with the State of California and are fully secured with eligible collateral at all times. The Letter of Credit Agreements are subject to annual maintenance charges and a fee of 15 basis points on issued amounts. As of June 30, 2018 , letters of credit totaling $140.0 million were issued in lieu of securities on deposit with the State of California under these Letter of Credit Agreements. As of June 30, 2018 , investment securities having a fair value of $258.7 million were pledged to FHLB by the Company's insurance subsidiaries in support of the collateralized advance facility and the Letter of Credit Agreements.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income	6 Months Ended
	Jun. 30, 2018
Accumulated Other Comprehensive Income [Abstract]
Accumulated Other Comprehensive Income, Net	Accumulated Other Comprehensive Income Accumulated other comprehensive income is comprised of unrealized (losses) gains on investments classified as AFS, net of deferred tax expense. Beginning in 2018, with the adoption of ASU No. 2016-01, the Company's investments in equity securities at fair value are no longer considered to be AFS and are reported at fair value with unrealized gains and losses included in Net realized and unrealized (losses) gains on investments on the Company's Consolidated Statements of Comprehensive Income. Prior to 2018, investments in equity securities at fair value were classified as AFS and changes in fair value were excluded from earnings and reported in accumulated other comprehensive income. The following table summarizes the components of accumulated other comprehensive (loss) income: June 30, 2018 December 31, 2017 (in millions) Net unrealized (losses) gains on investments, before taxes $ (16.8 ) $ 136.0 Deferred tax benefit (expense) on net unrealized (losses) gains 3.5 (28.6 ) Total accumulated other comprehensive (loss) income $ (13.3 ) $ 107.4

Stock-Based Compensation

Stock-Based Compensation	6 Months Ended
	Jun. 30, 2018
Stock-Based Compensation [Abstract]
Stock-Based compensation	Stock-Based Compensation The Company awarded restricted stock units (RSUs) and performance share units (PSUs) to certain employees and non-employee Directors of the Company as follows: Number Awarded Weighted Average Fair Value on Date of Grant Aggregate Fair Value on Date of Grant (in millions) March 2018 RSUs (1) 71,400 $ 40.30 $ 2.9 RSUs (2) 736 40.50 — PSUs (3) 96,940 40.30 3.9 May 2018 RSUs (4) 13,347 $ 39.65 $ 0.5 (1) The RSUs awarded in March 2018 were awarded to certain employees of the Company and vest 25% on March 15, 2019, and each of the subsequent three anniversaries of that date . The RSUs are subject to accelerated vesting in certain circumstances, including but not limited to: death, disability, retirement, or in connection with a change of control of the Company. (2) The RSUs awarded in March 2018 were awarded to non-employee Directors of the Company and vested in full on May 25, 2018 . (3) The PSUs awarded in March 2018 were awarded to certain employees of the Company and have a performance period of two years followed by an additional one year vesting period. The PSU awards are subject to certain performance goals with payouts that range from 0% to 200% of the target awards. The value shown in the table represents the aggregate number of PSUs awarded at the target level. (4) The RSUs awarded in May 2018 were awarded to non-employee Directors of the Company and vest in full on May 24, 2019 . Employees who were awarded RSUs and PSUs are entitled to receive dividend equivalents for eligible awards, payable in cash, when the underlying award vests and becomes payable. If the underlying award does not vest or is forfeited, any dividend equivalents with respect to the underlying award will also fail to become payable and will be forfeited. Stock options exercised totaled 13,800 for the six months ended June 30, 2018 , 167,026 for the six months ended June 30, 2017 , and 307,076 for the year ended December 31, 2017 . As of June 30, 2018 , the Company had 233,547 options, 313,426 RSUs, and 266,535 PSUs (based on target number awarded) outstanding.

Earnings Per Share

Earnings Per Share	6 Months Ended
	Jun. 30, 2018
Earnings Per Share [Abstract]
Earnings Per Share	Earnings Per Share Basic earnings per share is computed by dividing net income by the weighted average number of shares outstanding for the period. Diluted earnings per share reflects the potential dilutive impact of all common stock equivalents on earnings per share. Diluted earnings per share includes shares that are assumed to be issued under the “treasury stock method,” which reflects the potential dilution that would occur if outstanding RSUs and PSUs had vested and options were to be exercised. Commencing in 2017, certain stock-based compensation awards are eligible to receive dividend equivalents on awards that fully vest or become payable. The dividend equivalents are reflected in the Company's net income; therefore, these awards are not considered participating securities for the purposes of determining earnings per share. The following table presents the net income and the weighted average number of shares outstanding used in the earnings per common share calculations. Three Months Ended Six Months Ended June 30, June 30, 2018 2017 2018 2017 (in millions, except share data) Net income—basic and diluted $ 42.5 $ 24.8 $ 68.1 $ 48.0 Weighted average number of shares outstanding—basic 32,880,023 32,469,137 32,843,448 32,398,858 Effect of dilutive securities: PSUs 202,149 235,617 253,098 272,754 Stock options 100,357 230,049 100,635 227,856 RSUs 40,177 57,795 62,578 83,460 Dilutive potential shares 342,683 523,461 416,311 584,070 Weighted average number of shares outstanding—diluted 33,222,706 32,992,598 33,259,759 32,982,928

Changes in Estimates (Tables)

Changes in Estimates (Tables)	6 Months Ended
	Jun. 30, 2018
Changes in Estimates [Abstract]
Change Due to Estimated Reserves Ceded Under the LPT Agreement [Table Text Block]	The Company reduced its estimated loss and LAE reserves ceded under the Loss Portfolio Transfer Agreement (LPT Reserve Adjustment) as a result of the determination that an adjustment was necessary to reflect observed favorable paid loss trends during the second quarter of 2018 . The following table shows the financial statement impact related to the LPT Reserve Adjustment. Three Months Ended Six Months Ended June 30, 2018 June 30, 2018 (in millions, except per share data) LPT Reserve Adjustment $ (6.3 ) $ (6.3 ) Cumulative adjustment to the Deferred Gain (1) (2.2 ) (2.2 ) Net income impact from this change in estimate 2.2 2.2 Earnings per common share impact from this change in estimate: Basic and Diluted 0.07 0.07 (1) The cumulative adjustment to the Deferred reinsurance gain–LPT Agreement (Deferred Gain) was also recognized in losses and LAE incurred in the Company's Consolidated Statement of Comprehensive Income, so that the Deferred Gain reflects the balance that would have existed had the revised loss and LAE reserves been recognized at the inception of the LPT Agreement.
ChangetoContingentProfitCommission [Table Text Block]	The Company increased its estimate of Contingent commission receivable – LPT Agreement (LPT Contingent Commission Adjustment) as a result of the determination that an adjustment was necessary to reflect observed favorable paid loss trends during the second quarter of 2018 . The following table shows the financial statement impact related to the LPT Contingent Commission Adjustment. Three Months Ended Six Months Ended June 30, 2018 June 30, 2018 (in millions, except per share data) LPT Contingent Commission Adjustment $ 0.5 $ 0.5 Net income impact from this change in estimate 0.5 0.5 Earnings per common share impact from this change in estimate: Basic and Diluted 0.02 0.02

Fair Value of Financial Instr22

Fair Value of Financial Instruments (Tables)	6 Months Ended
	Jun. 30, 2018
Fair Value of Financial Instruments [Abstract]
Estimated fair value of financial instruments table	The carrying value and the estimated fair value of the Company’s financial instruments at fair value were as follows: June 30, 2018 December 31, 2017 Carrying Value Estimated Fair Value Carrying Value Estimated Fair Value (in millions) Financial assets Total investments at fair value $ 2,598.9 $ 2,598.9 $ 2,677.7 $ 2,677.7 Cash and cash equivalents 146.3 146.3 73.3 73.3 Restricted cash and cash equivalents 1.0 1.0 1.0 1.0 Financial liabilities Notes payable $ 20.0 $ 23.5 $ 20.0 $ 23.6
Fair value, assets and liabilities measured on recurring basis table	The following table presents the Company's investments at fair value and the corresponding fair value measurements. June 30, 2018 December 31, 2017 Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 (in millions) Fixed maturity securities: U.S. Treasuries $ — $ 119.4 $ — $ — $ 137.0 $ — U.S. Agencies — 11.5 — — 11.8 — States and municipalities — 568.7 — — 642.5 — Corporate securities — 1,079.5 — — 1,118.0 — Residential mortgage-backed securities — 433.1 — — 389.3 — Commercial mortgage-backed securities — 104.0 — — 106.0 — Asset-backed securities — 67.3 — — 58.8 — Other securities — 17.7 — — — — Total fixed maturity securities $ — $ 2,401.2 $ — $ — $ 2,463.4 $ — Equity securities at fair value: Industrial and miscellaneous $ 172.6 $ — $ — $ 181.7 $ — $ — Non-redeemable preferred stock (FHLB) — — — — — 4.7 Other 25.1 — — 23.9 — — Total equity securities at fair value 197.7 — — 205.6 — 4.7 Short-term investments — — — — 4.0 — Total investments at fair value $ 197.7 $ 2,401.2 $ — $ 205.6 $ 2,467.4 $ 4.7
Schedule of Cash and Cash Equivalents [Table Text Block]	The following table presents cash equivalents at NAV and total cash and cash equivalents carried at fair value on the Company's Consolidated Balance Sheets. June 30, 2018 December 31, 2017 (in millions) Cash and cash equivalents at fair value $ 61.3 $ 34.3 Cash equivalents measured at NAV, which approximates fair value 85.0 39.0 Total cash and cash equivalents $ 146.3 $ 73.3
Fair value, assets measured on recurring basis, unobservable input reconciliation table	The following table provides a reconciliation of the beginning and ending balances of investments that are recorded at fair value and are measured using Level 3 inputs for the six months ended June 30, 2018 and 2017 . Level 3 Securities 2018 2017 (in millions) Beginning balance, January 1 $ 4.7 $ 11.9 Transfers out of Level 3 (1) (4.7 ) (7.0 ) Purchases and sales, net — (0.2 ) Ending balance, June 30 $ — $ 4.7 (1) The transfer during the six months ended June 30, 2018 was the result of adoption of ASU 2016-01, which specified that FHLB stock shall be carried at cost and is no longer measured at fair value. Transfers during the six months ended June 30, 2017 were from Level 3 to Level 2 as observable market data became available for these securities.

Investments (Tables)

Investments (Tables)	6 Months Ended
	Jun. 30, 2018
Investments [Abstract]
Available-for-sale securities table	The cost or amortized cost, gross unrealized gains, gross unrealized losses, and estimated fair value of the Company’s AFS investments were as follows: Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value (in millions) At June 30, 2018 Fixed maturity securities U.S. Treasuries $ 120.4 $ 0.9 $ (1.9 ) $ 119.4 U.S. Agencies 11.3 0.3 (0.1 ) 11.5 States and municipalities 555.0 14.9 (1.2 ) 568.7 Corporate securities 1,095.9 6.5 (22.9 ) 1,079.5 Residential mortgage-backed securities 442.9 2.0 (11.8 ) 433.1 Commercial mortgage-backed securities 107.1 — (3.1 ) 104.0 Asset-backed securities 67.6 0.2 (0.5 ) 67.3 Other securities 17.8 — (0.1 ) 17.7 Total fixed maturity securities 2,418.0 24.8 (41.6 ) 2,401.2 Total AFS investments $ 2,418.0 $ 24.8 $ (41.6 ) $ 2,401.2 At December 31, 2017 Fixed maturity securities U.S. Treasuries $ 135.8 $ 2.0 $ (0.8 ) $ 137.0 U.S. Agencies 11.3 0.5 — 11.8 States and municipalities 617.0 25.5 — 642.5 Corporate securities 1,103.4 18.0 (3.4 ) 1,118.0 Residential mortgage-backed securities 388.3 3.6 (2.6 ) 389.3 Commercial mortgage-backed securities 106.5 0.4 (0.9 ) 106.0 Asset-backed securities 58.7 0.3 (0.2 ) 58.8 Total fixed maturity securities 2,421.0 50.3 (7.9 ) 2,463.4 Equity securities at fair value Industrial and miscellaneous 100.8 81.5 (0.6 ) 181.7 Non-redeemable preferred stock (FHLB) 4.7 — — 4.7 Other 11.2 12.7 — 23.9 Total equity securities at fair value 116.7 94.2 (0.6 ) 210.3 Short-term investments 4.0 — — 4.0 Total AFS investments $ 2,541.7 $ 144.5 $ (8.5 ) $ 2,677.7
Equity securities table	The cost and estimated fair value of the Company’s equity securities recorded at fair value at June 30, 2018 were as follows: Cost Estimated Fair Value (in millions) At June 30, 2018 Equity securities at fair value Industrial and miscellaneous $ 99.4 $ 172.6 Other 14.1 25.1 Total equity securities at fair value $ 113.5 $ 197.7
Investments classified by contractual maturity date table	The amortized cost and estimated fair value of the Company's fixed maturity securities at June 30, 2018 , by contractual maturity, are shown below. Expected maturities differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. Amortized Cost Estimated Fair Value (in millions) Due in one year or less $ 177.8 $ 178.3 Due after one year through five years 761.7 763.6 Due after five years through ten years 730.0 720.6 Due after ten years 130.9 134.3 Mortgage and asset-backed securities 617.6 604.4 Total $ 2,418.0 $ 2,401.2
Unrealized loss on investments table	The following is a summary of AFS investments that have been in a continuous unrealized loss position for less than 12 months and those that have been in a continuous unrealized loss position for 12 months or greater as of June 30, 2018 and December 31, 2017 . June 30, 2018 December 31, 2017 Estimated Fair Value Gross Number of Issues Estimated Fair Value Gross Number of Issues (in millions, except number of issues data) Less than 12 months: Fixed maturity securities U.S. Treasuries $ 82.0 $ (1.6 ) 27 $ 86.0 $ (0.5 ) 28 U.S. Agencies 3.7 (0.1 ) 2 — — — States and municipalities 84.0 (1.2 ) 24 — — — Corporate securities 811.5 (21.0 ) 265 307.6 (2.3 ) 113 Residential mortgage-backed securities 310.0 (8.1 ) 93 165.0 (0.8 ) 45 Commercial mortgage-backed securities 75.4 (2.0 ) 34 41.8 (0.2 ) 19 Asset-backed securities 53.1 (0.5 ) 37 29.3 (0.2 ) 25 Other securities 16.1 (0.1 ) 23 — — — Total less than 12 months $ 1,435.8 $ (34.6 ) 505 $ 629.7 $ (4.0 ) 230 12 months or greater: Fixed maturity securities U.S. Treasuries $ 17.7 $ (0.3 ) 9 $ 23.4 $ (0.3 ) 10 Corporate securities 36.1 (1.9 ) 15 53.2 (1.1 ) 17 Residential mortgage-backed securities 69.7 (3.7 ) 32 77.1 (1.8 ) 32 Commercial mortgage-backed securities 20.2 (1.1 ) 8 25.1 (0.7 ) 8 Total 12 months or greater $ 143.7 $ (7.0 ) 64 $ 178.8 $ (3.9 ) 67
Unrealized gain (loss) on investments	Net realized gains on investments and the change in unrealized gains (losses) on the Company's investments recorded at fair value are determined on a specific-identification basis and were as follows: Gross Realized Gains Gross Realized Losses Change in Net Unrealized Gains (Losses) Changes in Fair Value Reflected in Earnings Changes in Fair Value Reflected in AOCI, before tax (in millions) Three Months Ended June 30, 2018 Fixed maturity securities $ 0.3 $ (0.3 ) $ (14.3 ) $ — $ (14.3 ) Equity securities 2.6 (0.4 ) 3.5 5.7 — Total investments $ 2.9 $ (0.7 ) $ (10.8 ) $ 5.7 $ (14.3 ) Six Months Ended June 30, 2018 Fixed maturity securities $ 2.1 $ (2.6 ) $ (59.2 ) $ (0.5 ) $ (59.2 ) Equity securities 8.1 (0.6 ) (9.4 ) (1.9 ) — Total investments $ 10.2 $ (3.2 ) $ (68.6 ) $ (2.4 ) $ (59.2 ) Three Months Ended June 30, 2017 Fixed maturity securities $ — $ — $ 12.5 $ — $ 12.5 Equity securities 1.1 — (0.7 ) 1.1 (0.7 ) Total investments $ 1.1 $ — $ 11.8 $ 1.1 $ 11.8 Six Months Ended June 30, 2017 Fixed maturity securities $ 0.5 $ (0.1 ) $ 18.9 $ 0.4 $ 18.9 Equity securities 3.1 (0.2 ) 5.4 2.9 5.4 Total investments $ 3.6 $ (0.3 ) $ 24.3 $ 3.3 $ 24.3
Investment income table	Net investment income was as follows: Three Months Ended Six Months Ended June 30, June 30, 2018 2017 2018 2017 (in millions) Fixed maturity securities $ 19.2 $ 17.3 $ 37.7 $ 35.0 Equity securities 1.7 1.7 3.3 3.5 Cash equivalents and restricted cash 0.3 0.1 0.5 0.2 Gross investment income 21.2 19.1 41.5 38.7 Investment expenses (0.9 ) (0.9 ) (1.8 ) (1.8 ) Net investment income $ 20.3 $ 18.2 $ 39.7 $ 36.9

Liability for Unpaid Losses a24

Liability for Unpaid Losses and Loss Adjustment Expenses (Tables)	6 Months Ended
	Jun. 30, 2018
Liability for Unpaid Losses and Loss Adjustment Expenses [Abstract]
Changes in the liability for unpaid losses and LAE table	The following table represents a reconciliation of changes in the liability for unpaid losses and LAE. Three Months Ended Six Months Ended June 30, June 30, 2018 2017 2018 2017 (in millions) Unpaid losses and LAE at beginning of period $ 2,258.1 $ 2,298.2 $ 2,266.1 $ 2,301.0 Less reinsurance recoverable, excluding bad debt allowance, on unpaid losses and LAE 531.1 572.9 537.0 580.0 Net unpaid losses and LAE at beginning of period 1,727.0 1,725.3 1,729.1 1,721.0 Losses and LAE, net of reinsurance, incurred during the period related to: Current period 111.2 109.4 221.6 221.3 Prior periods (16.5 ) (0.3 ) (28.9 ) (0.3 ) Total net losses and LAE incurred during the period 94.7 109.1 192.7 221.0 Paid losses and LAE, net of reinsurance, related to: Current period 20.0 17.0 25.9 21.7 Prior periods 86.3 92.3 180.5 195.2 Total net paid losses and LAE during the period 106.3 109.3 206.4 216.9 Ending unpaid losses and LAE, net of reinsurance 1,715.4 1,725.1 1,715.4 1,725.1 Reinsurance recoverable, excluding bad debt allowance, on unpaid losses and LAE 512.5 559.8 512.5 559.8 Unpaid losses and LAE at end of period $ 2,227.9 $ 2,284.9 $ 2,227.9 $ 2,284.9

Notes Payable (Tables)

Notes Payable (Tables)	6 Months Ended
	Jun. 30, 2018
Notes Payable [Abstract]
Schedule of long-term debt instruments table	Notes payable is comprised of the following: June 30, 2018 December 31, 2017 (in millions) Dekania Surplus Note, due April 29, 2034 $ 10.0 $ 10.0 Alesco Surplus Note, due December 15, 2034 10.0 10.0 Total $ 20.0 $ 20.0

Accumulated Other Comprehensi26

Accumulated Other Comprehensive Income (Tables)	6 Months Ended
	Jun. 30, 2018
Accumulated Other Comprehensive Income [Abstract]
Schedule of accumulated other comprehensive income (loss) table	The following table summarizes the components of accumulated other comprehensive (loss) income: June 30, 2018 December 31, 2017 (in millions) Net unrealized (losses) gains on investments, before taxes $ (16.8 ) $ 136.0 Deferred tax benefit (expense) on net unrealized (losses) gains 3.5 (28.6 ) Total accumulated other comprehensive (loss) income $ (13.3 ) $ 107.4

Stock-Based Compensation Stock-

Stock-Based Compensation Stock-Based Compensation (Tables)	6 Months Ended
	Jun. 30, 2018
Stock-Based Compensation [Abstract]
Share-based compensation arrangements by share-based payment award table	The Company awarded restricted stock units (RSUs) and performance share units (PSUs) to certain employees and non-employee Directors of the Company as follows: Number Awarded Weighted Average Fair Value on Date of Grant Aggregate Fair Value on Date of Grant (in millions) March 2018 RSUs (1) 71,400 $ 40.30 $ 2.9 RSUs (2) 736 40.50 — PSUs (3) 96,940 40.30 3.9 May 2018 RSUs (4) 13,347 $ 39.65 $ 0.5 (1) The RSUs awarded in March 2018 were awarded to certain employees of the Company and vest 25% on March 15, 2019, and each of the subsequent three anniversaries of that date . The RSUs are subject to accelerated vesting in certain circumstances, including but not limited to: death, disability, retirement, or in connection with a change of control of the Company. (2) The RSUs awarded in March 2018 were awarded to non-employee Directors of the Company and vested in full on May 25, 2018 . (3) The PSUs awarded in March 2018 were awarded to certain employees of the Company and have a performance period of two years followed by an additional one year vesting period. The PSU awards are subject to certain performance goals with payouts that range from 0% to 200% of the target awards. The value shown in the table represents the aggregate number of PSUs awarded at the target level. (4) The RSUs awarded in May 2018 were awarded to non-employee Directors of the Company and vest in full on May 24, 2019 .

Earnings Per Share (Tables)

Earnings Per Share (Tables)	6 Months Ended
	Jun. 30, 2018
Earnings Per Share [Abstract]
Net income and weighted average common shares outstanding used in earnings per share calculations table	The following table presents the net income and the weighted average number of shares outstanding used in the earnings per common share calculations. Three Months Ended Six Months Ended June 30, June 30, 2018 2017 2018 2017 (in millions, except share data) Net income—basic and diluted $ 42.5 $ 24.8 $ 68.1 $ 48.0 Weighted average number of shares outstanding—basic 32,880,023 32,469,137 32,843,448 32,398,858 Effect of dilutive securities: PSUs 202,149 235,617 253,098 272,754 Stock options 100,357 230,049 100,635 227,856 RSUs 40,177 57,795 62,578 83,460 Dilutive potential shares 342,683 523,461 416,311 584,070 Weighted average number of shares outstanding—diluted 33,222,706 32,992,598 33,259,759 32,982,928

Basis of Presentation Pending P

Basis of Presentation Pending Purchase of PRUS (Details) $ in Millions	6 Months Ended
	Jun. 30, 2018USD ($)
Business Acquisition [Line Items]
Estimated statutory capital and surplus of pending acquisition	$ 40
Net cash payment to acquire business	$ 5.8

Changes in Estimates (Details)

Changes in Estimates (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Change in Accounting Estimate [Line Items]
Net income		$ 42,500	$ 24,800	$ 68,100	$ 48,000
Change Due to Estimated Reserves Ceded Under the LPT Agreement [Member]
Change in Accounting Estimate [Line Items]
LPT reserve adjustment		(6,300)		(6,300)
Cumulative adjustment to the Deferred Gain	[1]	(2,200)		(2,200)
Net income		$ 2,200		$ 2,200
Basic and Diluted		$ 0.07		$ 0.07
Change to Contingent Profit Commission [Member]
Change in Accounting Estimate [Line Items]
Net income		$ 500		$ 500
Change in estimate of contingent commission receivable		$ 500		$ 500
Basic and Diluted		$ 0.02		$ 0.02
[1]	The cumulative adjustment to the Deferred reinsurance gain–LPT Agreement (Deferred Gain) was also recognized in losses and LAE incurred in the Company's Consolidated Statement of Comprehensive Income, so that the Deferred Gain reflects the balance that would have existed had the revised loss and LAE reserves been recognized at the inception of the LPT Agreement.

New Accounting Standards Adopte

New Accounting Standards Adopted ASU (Details) - Accounting Standards Update 2016-01 [Member] $ in Millions	Jun. 30, 2018USD ($)
Reclassification adjustment for adoption of ASU	$ 0
Accumulated Other Comprehensive Income, Net
Reclassification adjustment for adoption of ASU	(74)
Retained Earnings
Reclassification adjustment for adoption of ASU	$ 74

New Accounting Standards Not Ye

New Accounting Standards Not Yet Adopted ASU (Details) $ in Millions	Jun. 30, 2018USD ($)
Accounting Standards Update 2016-02 [Member]
Operating Lease, Liability	$ 23

Fair Value of Financial Instr33

Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments at fair value	$ 2,598,900	$ 2,677,700
Total Investments at fair value, estimated fair value	2,598,900	2,677,700
Cash and cash equivalents	146,300	73,300
Cash and cash equivalents, estimated fair value	146,300	73,300
Equity securities at cost	6,400	0
Restricted cash and cash equivalents	1,000	1,000
Notes payable	20,000	20,000
Notes Payable, estimated fair value	23,500	23,600
Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Restricted cash and cash equivalents	$ 1,000	$ 1,000

Fair Value of Financial Instr34

Fair Value of Financial Instruments, Fair Value Inputs (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	$ 2,401.2	$ 2,677.7
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	197.7	205.6
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	2,401.2	2,467.4
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	4.7
Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	2,401.2	2,463.4
Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	2,401.2	2,463.4
Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
US Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	119.4	137
US Treasury Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
US Treasury Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	119.4	137
US Treasury Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	11.5	11.8
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	11.5	11.8
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
US States and Political Subdivisions Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	568.7	642.5
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	568.7	642.5
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	1,079.5	1,118
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	1,079.5	1,118
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Residential Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	433.1	389.3
Residential Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Residential Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	433.1	389.3
Residential Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Commercial Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	104	106
Commercial Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Commercial Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	104	106
Commercial Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	67.3	58.8
Asset-backed Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Asset-backed Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	67.3	58.8
Asset-backed Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Other Debt Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	17.7
Other Debt Obligations [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Other Debt Obligations [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	17.7	0
Other Debt Obligations [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		210.3
Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	197.7	205.6
Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	4.7
Industrial and Miscellaneous [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		181.7
Industrial and Miscellaneous [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	172.6	181.7
Industrial and Miscellaneous [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Industrial and Miscellaneous [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Non-redeemable preferred (FHLB stock) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		4.7
Non-redeemable preferred (FHLB stock) [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Non-redeemable preferred (FHLB stock) [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Non-redeemable preferred (FHLB stock) [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	4.7
Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		23.9
Other [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	25.1	23.9
Other [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Other [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Short-term Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	4
Short-term Investments [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	0	0
Short-term Investments [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments		4
Short-term Investments [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	$ 0	$ 0

Fair Value of Financial Instr35

Fair Value of Financial Instruments Cash Equivalents at NAV and Total Cash and Cash Equivalents Carried at Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents at fair value	$ 61.3	$ 34.3
Cash equivalents measured at NAV, which approximates fair value	85	39
Total cash and cash equivalents	$ 146.3	$ 73.3

Fair Value of Financial Instr36

Fair Value of Financial Instruments Fair Value of Financial Instruments, Reconciliation of Level 3 Securities (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018		Jun. 30, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance, January 1	$ 2,677,700
Ending balance, March 31	2,605,300
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance, January 1	4,700		$ 11,900
Transfers out of Level 3 (1)	(4,700)	[1]	(7,000)
Purchases and sales, net	0		(200)
Ending balance, March 31	$ 0		$ 4,700
[1]	(1)The transfer during the six months ended June 30, 2018 was the result of adoption of ASU 2016-01, which specified that FHLB stock shall be carried at cost and is no longer measured at fair value. Transfers during the six months ended June 30, 2017 were from Level 3 to Level 2 as observable market data became available for these securities.

Investments Available for Sale

Investments Available for Sale Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 2,418,000	$ 2,541,700
Gross unrealized gain	24,800	144,500
Gross unrealized loss	(41,600)	(8,500)
Investments	2,401,200	2,677,700
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	2,418,000	2,421,000
Gross unrealized gain	24,800	50,300
Gross unrealized loss	(41,600)	(7,900)
Investments	2,401,200	2,463,400
US Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	120,400	135,800
Gross unrealized gain	900	2,000
Gross unrealized loss	(1,900)	(800)
Investments	119,400	137,000
US Government Agencies Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	11,300	11,300
Gross unrealized gain	300	500
Gross unrealized loss	(100)	0
Investments	11,500	11,800
US States and Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	555,000	617,000
Gross unrealized gain	14,900	25,500
Gross unrealized loss	(1,200)	0
Investments	568,700	642,500
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	1,095,900	1,103,400
Gross unrealized gain	6,500	18,000
Gross unrealized loss	(22,900)	(3,400)
Investments	1,079,500	1,118,000
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	442,900	388,300
Gross unrealized gain	2,000	3,600
Gross unrealized loss	(11,800)	(2,600)
Investments	433,100	389,300
Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	107,100	106,500
Gross unrealized gain	0	400
Gross unrealized loss	(3,100)	(900)
Investments	104,000	106,000
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	67,600	58,700
Gross unrealized gain	200	300
Gross unrealized loss	(500)	(200)
Investments	67,300	58,800
Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	17,800
Gross unrealized gain	0
Gross unrealized loss	(100)
Investments	17,700
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost		116,700
Gross unrealized gain		94,200
Gross unrealized loss		(600)
Investments		210,300
Industrial and Miscellaneous [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost		100,800
Gross unrealized gain		81,500
Gross unrealized loss		(600)
Investments		181,700
Non-redeemable preferred (FHLB stock) [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost		4,700
Gross unrealized gain		0
Gross unrealized loss		0
Investments		4,700
Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost		11,200
Gross unrealized gain		12,700
Gross unrealized loss		0
Investments		23,900
Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost		4,000
Gross unrealized gain		0
Gross unrealized loss		0
Investments	$ 0	$ 4,000

Investments Equity Securities (

Investments Equity Securities (Details) $ in Thousands	Jun. 30, 2018USD ($)
Schedule of Equity Securities and Other [Line Items]
Equity securities at fair value, cost	$ 113,500
Equity securities, estimated fair value	197,700
Industrial and Miscellaneous [Member]
Schedule of Equity Securities and Other [Line Items]
Equity securities at fair value, cost	99,400
Equity securities, estimated fair value	172,600
Other [Member]
Schedule of Equity Securities and Other [Line Items]
Equity securities at fair value, cost	14,100
Equity securities, estimated fair value	$ 25,100

Investments, Amortized Cost and

Investments, Amortized Cost and Estimated Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Amortized Cost
Due in one year or less, amortized cost	$ 177,800
Due after one year through five years, amortized cost	761,700
Due after five years through ten years, amortized cost	730,000
Due after ten years, amortized cost	130,900
Mortgage and asset-backed securities, amortized cost	617,600
Total, amortized cost	2,418,000
Estimated Fair Value
Due in one year or less, fair value	178,300
Due after one year through five years, fair value	763,600
Due after five years through ten years, fair value	720,600
Due after ten years, fair value	134,300
Mortgage and asset-backed securities, fair value	604,400
Total, fair value	$ 2,401,200	$ 2,463,400

Investments, Continuous Loss Po

Investments, Continuous Loss Position (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2018USD ($)shares	Jun. 30, 2017USD ($)shares	Jun. 30, 2018USD ($)shares	Jun. 30, 2017USD ($)shares	Dec. 31, 2017USD ($)shares
Estimated Fair Value
Estimated fair value, less than 12 months	$ 1,435,800,000		$ 1,435,800,000		$ 629,700,000
Estimated fair value, 12 months or greater	143,700,000		143,700,000		178,800,000
Gross Unrealized Losses
Gross unrealized losses, less than 12 months	(34,600,000)		(34,600,000)		(4,000,000)
Gross unrealized losses, 12 months or greater	$ (7,000,000)		$ (7,000,000)		$ (3,900,000)
Number of issues in loss position, less than 12 months	505		505		230
Number of Issues in loss position, 12 months or greater	64		64		67
Other than temporary impairment, credit losses recognized in earnings	$ 0	$ 0	$ 2,000,000	$ 200,000
Debt Securities [Member]
Gross Unrealized Losses
Other than temporary impairment, credit losses recognized in earnings			$ 2,000,000
Total impairments, number of securities | shares	57	0	57	0
US Treasury Securities [Member]
Estimated Fair Value
Estimated fair value, less than 12 months	$ 82,000,000		$ 82,000,000		$ 86,000,000
Estimated fair value, 12 months or greater	17,700,000		17,700,000		23,400,000
Gross Unrealized Losses
Gross unrealized losses, less than 12 months	(1,600,000)		(1,600,000)		(500,000)
Gross unrealized losses, 12 months or greater	$ (300,000)		$ (300,000)		$ (300,000)
Number of issues in loss position, less than 12 months	27		27		28
Number of Issues in loss position, 12 months or greater	9		9		10
US Government Agencies Debt Securities [Member]
Estimated Fair Value
Estimated fair value, less than 12 months	$ 3,700,000		$ 3,700,000		$ 0
Gross Unrealized Losses
Gross unrealized losses, less than 12 months	$ (100,000)		$ (100,000)		$ 0
Number of issues in loss position, less than 12 months	2		2		0
US States and Political Subdivisions Debt Securities [Member]
Estimated Fair Value
Estimated fair value, less than 12 months	$ 84,000,000		$ 84,000,000		$ 0
Gross Unrealized Losses
Gross unrealized losses, less than 12 months	$ (1,200,000)		$ (1,200,000)		$ 0
Number of issues in loss position, less than 12 months	24		24		0
Corporate Debt Securities [Member]
Estimated Fair Value
Estimated fair value, less than 12 months	$ 811,500,000		$ 811,500,000		$ 307,600,000
Estimated fair value, 12 months or greater	36,100,000		36,100,000		53,200,000
Gross Unrealized Losses
Gross unrealized losses, less than 12 months	(21,000,000)		(21,000,000)		(2,300,000)
Gross unrealized losses, 12 months or greater	$ (1,900,000)		$ (1,900,000)		$ (1,100,000)
Number of issues in loss position, less than 12 months	265		265		113
Number of Issues in loss position, 12 months or greater	15		15		17
Residential Mortgage Backed Securities [Member]
Estimated Fair Value
Estimated fair value, less than 12 months	$ 310,000,000		$ 310,000,000		$ 165,000,000
Estimated fair value, 12 months or greater	69,700,000		69,700,000		77,100,000
Gross Unrealized Losses
Gross unrealized losses, less than 12 months	(8,100,000)		(8,100,000)		(800,000)
Gross unrealized losses, 12 months or greater	$ (3,700,000)		$ (3,700,000)		$ (1,800,000)
Number of issues in loss position, less than 12 months	93		93		45
Number of Issues in loss position, 12 months or greater	32		32		32
Commercial Mortgage Backed Securities [Member]
Estimated Fair Value
Estimated fair value, less than 12 months	$ 75,400,000		$ 75,400,000		$ 41,800,000
Estimated fair value, 12 months or greater	20,200,000		20,200,000		25,100,000
Gross Unrealized Losses
Gross unrealized losses, less than 12 months	(2,000,000)		(2,000,000)		(200,000)
Gross unrealized losses, 12 months or greater	$ (1,100,000)		$ (1,100,000)		$ (700,000)
Number of issues in loss position, less than 12 months	34		34		19
Number of Issues in loss position, 12 months or greater	8		8		8
Asset-backed Securities [Member]
Estimated Fair Value
Estimated fair value, less than 12 months	$ 53,100,000		$ 53,100,000		$ 29,300,000
Gross Unrealized Losses
Gross unrealized losses, less than 12 months	$ (500,000)		$ (500,000)		$ (200,000)
Number of issues in loss position, less than 12 months	37		37		25
Equity Securities [Member]
Gross Unrealized Losses
Gross unrealized losses, less than 12 months					$ (600,000)
Number of issues in loss position, less than 12 months | shares					24
Other than temporary impairment, credit losses recognized in earnings				$ 200,000
Total impairments, number of securities | shares		1		1
Other Debt Obligations [Member]
Estimated Fair Value
Estimated fair value, less than 12 months	$ 16,100,000		$ 16,100,000		$ 0
Gross Unrealized Losses
Gross unrealized losses, less than 12 months	$ (100,000)		$ (100,000)		$ 0
Number of issues in loss position, less than 12 months	23		23		0

Investments Investments, Net Re

Investments Investments, Net Realized Gains and Losses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
AFS, change in unrealized gains (losses)
AFS, change unrealized gains (losses) on fixed maturity and equity securities reflected in AOCI	$ (14,300)	$ 11,800	$ (59,200)	$ 24,300
AFS, net realized gains (losses)
AFS, Gross gains from sales		1,100		3,600
AFS, Gross losses from sales		0		(300)
Net realized (losses) gains on investments	5,700	1,100		3,300
Net realized and unrealized (losses) gains on investments	5,700	1,100	(2,400)	3,300
Total gross realized gains	2,900		10,200
Total gross realized losses	(700)		(3,200)
Total change in net unrealized gains (losses)	(10,800)		(68,600)
Debt Securities [Member]
AFS, change in unrealized gains (losses)
AFS, change unrealized gains (losses) on fixed maturity and equity securities reflected in AOCI	(14,300)	12,500	(59,200)	18,900
AFS, net realized gains (losses)
AFS, Gross gains from sales	300	0	2,100	500
AFS, Gross losses from sales	(300)	0	(2,600)	(100)
Net realized (losses) gains on investments		0		400
Net realized and unrealized (losses) gains on investments	0		(500)
Equity Securities [Member]
Equity securities:
Equity securities, gross realized gain	2,600		8,100
Equity securities, gross realized loss	(400)		(600)
Equity securities, change in unrealized gains (losses)	3,500		(9,400)
AFS, change in unrealized gains (losses)
AFS, change unrealized gains (losses) on fixed maturity and equity securities reflected in AOCI	0	(700)	0	5,400
AFS, net realized gains (losses)
AFS, Gross gains from sales		1,100		3,100
AFS, Gross losses from sales		0		(200)
Net realized (losses) gains on investments		$ 1,100		$ 2,900
Net realized and unrealized (losses) gains on investments	$ 5,700		$ (1,900)

Net Investment Income (Details)

Net Investment Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 21.2	$ 19.1	$ 41.5	$ 38.7
Investment expenses	0.9	0.9	1.8	1.8
Net investment income	20.3	18.2	39.7	36.9
Debt Securities [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income related to fixed maturity securities and short-term investments and cash equivalents	19.2	17.3	37.7	35
Equity Securities [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income related to equity securities	1.7	1.7	3.3	3.5
Short-term Investments [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income related to fixed maturity securities and short-term investments and cash equivalents	$ 0.3	$ 0.1	$ 0.5	$ 0.2

Investments Investments, Held i

Investments Investments, Held in Trust or on Deposit (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Deposit Assets [Abstract]
Investments	$ 2,605,300	$ 2,677,700
Assets Held-in-trust [Abstract]
Funds Held under Reinsurance Agreements, Asset	22,900	24,500
Federal Home Loan Bank [Member]
Deposit Assets [Abstract]
Investments	140,000
Required by various state laws and regulations to hold securities or letters of credit in depository account [Member]
Deposit Assets [Abstract]
Investments	$ 954,400	$ 1,009,700

Income Taxes (Details)

Income Taxes (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]
Statutory tax rate			21.00%	35.00%
Effective tax rate	17.20%	23.90%	15.60%	22.70%

Liability for Unpaid Losses a45

Liability for Unpaid Losses and Loss Adjustment Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Unpaid losses and LAE at beginning of period	$ 2,258,100	$ 2,298,200	$ 2,266,100	$ 2,301,000
Less reinsurance recoverable, excluding bad debt allowance, on unpaid losses and LAE	531,100	572,900	537,000	580,000
Net unpaid losses and LAE at beginning of period	1,727,000	1,725,300	1,729,100	1,721,000
Losses and LAE, net of reinsurance, incurred during the period related to:
Current period	111,200	109,400	221,600	221,300
Prior periods	(16,500)	(300)	(28,900)	(300)
Total net losses and LAE incurred during the period	94,700	109,100	192,700	221,000
Deduct payments for losses and LAE, net of reinsurance, related to:
Current period	20,000	17,000	25,900	21,700
Prior periods	86,300	92,300	180,500	195,200
Total net paid losses and LAE during the period	106,300	109,300	206,400	216,900
Ending unpaid losses and LAE, net of reinsurance	1,715,400	1,725,100	1,715,400	1,725,100
Reinsurance recoverable, excluding bad debt allowance, on unpaid losses and LAE	512,500	559,800	512,500	559,800
Unpaid losses and LAE at end of period	2,227,900	2,284,900	2,227,900	2,284,900
LPT Agreement [Abstract]
Impact of the LPT Agreement	6,900	$ 3,100	9,500	$ 6,000
Involuntary Assigned Risk Business [Member]
Losses and LAE, net of reinsurance, incurred during the period related to:
Prior periods			(400)
Voluntary Risk Business [Member]
Losses and LAE, net of reinsurance, incurred during the period related to:
Prior periods	$ (16,500)		$ (28,500)

LPT Agreement LPT Agreement (De

LPT Agreement LPT Agreement (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Reinsurance Agreement [Line Items]
Impact of the LPT Agreement		$ 6,900	$ 3,100	$ 9,500	$ 6,000
Liabilities for the incurred but unpaid losses and LAE related to claims prior to July 1, 1995		1,500,000		1,500,000
Ceded premiums written				775,000
Amortization of deferred gain		4,200	$ 3,100	6,800	$ 6,000
Deferred reinsurance gain—LPT Agreement		154,700		154,700		$ 163,600
Estimated remaining liabilities - LPT Agreement		420,300		420,300		438,900
Paid losses and LAE claims related to LPT		761,600		761,600		$ 749,300
Indemnification Agreement [Member]
Reinsurance Agreement [Line Items]
Coverage provided under LPT Agreement		2,000,000		2,000,000
Change Due to Estimated Reserves Ceded Under the LPT Agreement [Member]
Reinsurance Agreement [Line Items]
LPT reserve adjustment	[1]	2,200		2,200
Change to Contingent Profit Commission [Member]
Reinsurance Agreement [Line Items]
Change in estimate of contingent commission receivable		$ 500		$ 500
[1]	The cumulative adjustment to the Deferred reinsurance gain–LPT Agreement (Deferred Gain) was also recognized in losses and LAE incurred in the Company's Consolidated Statement of Comprehensive Income, so that the Deferred Gain reflects the balance that would have existed had the revised loss and LAE reserves been recognized at the inception of the LPT Agreement.

Notes Payable Notes Payable Out

Notes Payable Notes Payable Outstanding(Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Notes payable	$ 20,000	$ 20,000
Dekania Surplus Note [Member]
Debt Instrument [Line Items]
Notes payable	$ 10,000	10,000
Notes payable, maturity date	Apr. 30, 2034
Notes payable, callable	2,009
Interest rate, basis points in excess of the 90-day LIBOR	425
Alesco Surplus Note [Member]
Debt Instrument [Line Items]
Notes payable	$ 10,000	$ 10,000
Notes payable, maturity date	Dec. 15, 2034
Notes payable, callable	2,009
Interest rate, basis points in excess of the 90-day LIBOR	405

Notes Payable Letters of Credit

Notes Payable Letters of Credit (Details) $ in Millions	6 Months Ended
	Jun. 30, 2018USD ($)
Letters of Credit Facilities [Line Items]
Letters of credit, unused capacity, commitment fee percentage	0.15%
Federal Home Loan Bank [Member]
Letters of Credit Facilities [Line Items]
Letters of credit facilities, maximum borrowing capacity	$ 140
Letters of credit collateral amount	258.7
Federal Home Loan Bank [Member] | EAC
Letters of Credit Facilities [Line Items]
Letters of credit facilities, maximum borrowing capacity	40
Federal Home Loan Bank [Member] | ECIC
Letters of Credit Facilities [Line Items]
Letters of credit facilities, maximum borrowing capacity	50
Federal Home Loan Bank [Member] | EPIC
Letters of Credit Facilities [Line Items]
Letters of credit facilities, maximum borrowing capacity	$ 50

Accumulated Other Comprehensi49

Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Net unrealized gain on investments, before taxes	$ (16,800)	$ 136,000
Deferred tax expense on net unrealized gains	3,500	(28,600)
Accumulated other comprehensive income, net	$ (13,300)	$ 107,400

Stock-Based Compensation (Detai

Stock-Based Compensation (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended	3 Months Ended	6 Months Ended		12 Months Ended
		May 31, 2018	Mar. 31, 2018	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-options exercised				13,800	167,026	307,076
Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rights for RSUs awarded			vest 25% on March 15, 2019, and each of the subsequent three anniversaries of that date
Performance share awards performance period			two years
Performance share awards, minimum payout			0.00%
Performance share awards, maximum payout			200.00%
Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rights for RSUs awarded		vest in full on May 24, 2019	vested in full on May 25, 2018
Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of outstanding options or share units				233,547
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation award, shares issued	[1]	13,347
Share-based compensation options, exercise price on grant date	[1]	$ 39.65
Fair value of awards awarded on grant date	[1]	$ 0.5
Number of outstanding options or share units				313,426
Restricted Stock Units (RSUs) [Member] | Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation award, shares issued	[2]		71,400
Share-based compensation options, exercise price on grant date	[2]		$ 40.30
Fair value of awards awarded on grant date	[2]		$ 2.9
Restricted Stock Units (RSUs) [Member] | Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation award, shares issued	[3]		736
Share-based compensation options, exercise price on grant date	[3]		$ 40.50
Fair value of awards awarded on grant date	[3]		$ 0
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of outstanding options or share units				266,535
Performance Shares [Member] | Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation award, shares issued	[4]		96,940
Share-based compensation options, exercise price on grant date	[4]		$ 40.30
Fair value of awards awarded on grant date	[4]		$ 3.9
Share-based compensation arrangement by share-based payment award, award vesting period			1 year
[1]	The RSUs awarded in May 2018 were awarded to non-employee Directors of the Company and vest in full on May 24, 2019.
[2]	The RSUs awarded in March 2018 were awarded to certain employees of the Company and vest 25% on March 15, 2019, and each of the subsequent three anniversaries of that date. The RSUs are subject to accelerated vesting in certain circumstances, including but not limited to: death, disability, retirement, or in connection with a change of control of the Company.
[3]	The RSUs awarded in March 2018 were awarded to non-employee Directors of the Company and vested in full on May 25, 2018
[4]	The PSUs awarded in March 2018 were awarded to certain employees of the Company and have a performance period of two years followed by an additional one year vesting period. The PSU awards are subject to certain performance goals with payouts that range from 0% to 200% of the target awards. The value shown in the table represents the aggregate number of PSUs awarded at the target level.

Earnings Per Share (Details)

Earnings Per Share (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Net income available to stockholders - basic and diluted	$ 42,500	$ 24,800	$ 68,100	$ 48,000
Weighted average number of shares outstanding - basic	32,880,023	32,469,137	32,843,448	32,398,858
Effect of dilutive securities:
Dilutive securities	342,683	523,461	416,311	584,070
Weighted average number of shares outstanding - diluted	33,222,706	32,992,598	33,259,759	32,982,928
Performance Shares [Member]
Effect of dilutive securities:
Dilutive securities	202,149	235,617	253,098	272,754
Employee Stock Option [Member]
Effect of dilutive securities:
Dilutive securities	100,357	230,049	100,635	227,856
Restricted Stock Units (RSUs) [Member]
Effect of dilutive securities:
Dilutive securities	40,177	57,795	62,578	83,460

Uncategorized Items - eig-20180

Label	Element	Value
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	$ 147,300,000