State Auto Financial (STFC) 10-Q 1 Nov 19 2019 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2019	Oct. 25, 2019
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2019
Document Transition Report	false
Entity File Number	000-19289
Entity Registrant Name	STATE AUTO FINANCIAL CORPORATION
Entity Central Index Key	0000874977
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Incorporation, State or Country Code	OH
Entity Tax Identification Number	31-1324304
Entity Address, Address Line One	518 East Broad Street
Entity Address, State or Province	OH
Entity Address, City or Town	Columbus
Entity Address, Postal Zip Code	43215-3976
City Area Code	614
Local Phone Number	464-5000
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	false
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding (shares)		43,563,019
NASDAQ/NGS (GLOBAL SELECT MARKET) [Member]
Entity Information [Line Items]
Title of 12(b) Security	Common shares, without par value
Trading Symbol	STFC
Security Exchange Name	NASDAQ

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Document Period End Date	Sep. 30, 2019
Assets
Fixed maturities, available-for-sale, at fair value (amortized cost $2,129.0 and $2,188.2, respectively)	$ 2,189.3	$ 2,159.5
Equity securities	373.3	315
Other invested assets	64.6	48.8
Other invested assets, at cost	6.5	5.6
Notes receivable from affiliate	70	70
Total investments	2,703.7	2,598.9
Cash and cash equivalents	38.3	59.8
Accrued investment income and other assets	34.7	32.4
Deferred policy acquisition costs (affiliated net assumed $53.0 and $48.3, respectively)	114.3	101.9
Reinsurance recoverable on losses and loss expenses payable	7.2	5.5
Prepaid reinsurance premiums	7.5	6.6
Due from Affiliates	17.4	0
Current federal income taxes	6.3	5.9
Net deferred federal income taxes	46.2	77.8
Property and equipment, at cost	4.2	7.1
Total assets	2,979.8	2,895.9
Liabilities and Stockholders’ Equity
Losses and loss expenses payable (affiliated net assumed $521.5 and $593.6, respectively)	1,092.7	1,146.8
Unearned premiums (affiliated net assumed $111.7 and $112.4, respectively)	649.2	584.2
Notes payable (affiliates $15.2 and $15.2, respectively)	122	122
Pension and postretirement benefits	70.3	83
Due to Affiliate	0	22.4
Other liabilities (affiliated net assumed $13.1 and $19.9, respectively)	101.9	119
Total liabilities	2,036.1	2,077.4
Stockholders’ equity:
Common stock, without par value. Authorized 100.0 shares; 50.3 and 50.0 shares issued, respectively, at stated value of $2.50 per share	125.8	125
Treasury stock, 6.8 and 6.8 shares, respectively, at cost	(117.5)	(117)
Additional paid-in capital	205.2	194.2
Accumulated other comprehensive loss	(24.2)	(96.4)
Retained earnings	754.4	712.7
Total stockholders’ equity	943.7	818.5
Total liabilities and stockholders’ equity	2,979.8	2,895.9
Class A Preferred Stock [Member]
Stockholders’ equity:
Preferred stock value	0	0
Class B Preferred Stock [Member]
Stockholders’ equity:
Preferred stock value	$ 0	$ 0

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Fixed maturities, available-for-sale, amortized cost	$ 2,129	$ 2,188.2
Deferred policy acquisitions costs from affiliates	53	48.3
Losses and loss expenses payable, affiliates	521.5	593.6
Unearned premiums, affiliates	111.7	112.4
Notes payable, affiliates	15.2	15.2
Net Other Liabilities from Affiliates	$ 13.1	$ 19.9
Common stock, no par value (usd per share)	$ 0	$ 0
Common stock, shares authorized (shares)	100,000,000	100,000,000
Common stock, shares issued (shares)	50,300,000	50,000,000
Common stock, stated value per share (usd per share)	$ 2.50	$ 2.50
Treasury stock (shares)	6,800,000	6,800,000
Class A Preferred Stock [Member]
Preferred stock, no par value (usd per share)	$ 0	$ 0
Preferred stock, shares authorized (shares)	2,500,000	2,500,000
Preferred stock, shares issued (shares)	0	0
Class B Preferred Stock [Member]
Preferred stock, no par value (usd per share)	$ 0	$ 0
Preferred stock, shares authorized (shares)	2,500,000	2,500,000
Preferred stock, shares issued (shares)	0	0

Condensed Consolidated Statemen

Condensed Consolidated Statements of Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Earned premiums (affiliated net assumed $71.9 and $115.3, respectively, and $251.1 and $349.0, respectively)	$ 319.6	$ 306.8	$ 930	$ 929.2
Net investment income (affiliate $1.3 and $1.3, respectively, and $3.7 and $3.7, respectively)	19.3	20.8	60.4	62.2
Net realized gains on investments:
Total net realized gains on investments	(5)	17.8	50.2	18.2
Other income from affiliates	0.6	0.6	1.6	1.8
Total revenues	334.5	346	1,042.2	1,011.4
Losses and loss expenses (affiliated net assumed $34.7 and $128.9, respectively, and $105.4 and $298.8, respectively)	208.4	191	637.6	621.1
Acquisition and operating expenses (affiliated net ceded $26.8 and affiliated net assumed $78.9, respectively, and $52.3 and $231.0, respectively)	109.7	110.9	325.2	333
Interest expense (affiliates $0.2 and $0.2, respectively, and $0.7 and $0.6, respectively)	1.2	1.2	3.7	4.5
Other expenses	2.5	1.9	9	7.4
Costs and Expenses	321.8	305	975.5	966
Income before federal income taxes	12.7	41	66.7	45.4
Current Income Tax Expense (Benefit)	0	(0.1)	(0.4)	(1.1)
Deferred Income Tax Expense (Benefit)	1.2	7.7	12.4	9.2
Federal income tax expense	1.2	7.6	12	8.1
Net income	$ 11.5	$ 33.4	$ 54.7	$ 37.3
Earnings per common share:
Basic (usd per share)	$ 0.26	$ 0.78	$ 1.26	$ 0.87
Diluted (usd per share)	0.25	0.76	1.25	0.86
Dividends paid per common share (usd per share)	$ 0.10	$ 0.10	$ 0.30	$ 0.30

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Earned premiums, from affiliates	$ 55.7	$ 71.9	$ 168.5	$ 251.1
Net investment income, from affiliate	0.7	1.3	2.3	3.7
Losses and loss expenses, from affiliates	24.2	43	125.1	136.3
Net Acquisition and Operating Expenses, from affiliates	17.6	(26.8)	54.5	52.3
Interest Expense Debt To Affiliates	$ 0.2	$ 0.2	$ 0.7	$ 0.7

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 11.5	$ 33.4	$ 54.7	$ 37.3
Net unrealized holding gain (loss) on fixed available-for-sale investments:
Unrealized holding gain (loss)	22.6	(14.7)	91.8	(61.6)
Reclassification adjustments for gains realized in net income	(1.2)	0	(2.8)	(1.7)
Income tax (expense) benefit	(4.5)	3.1	(18.7)	13.3
Total net unrealized holding gain (loss) on available-for-sale investments	16.9	(11.6)	70.3	(50)
Reclassification adjustments for amortization to statements of income:
Negative prior service cost	(1.6)	(1.6)	(4.8)	(4.8)
Net actuarial loss	2.4	3.3	7.2	9.9
Income tax expense	(0.2)	(0.4)	(0.5)	(1.1)
Total net unrecognized benefit plan obligations	0.6	1.3	1.9	4
Other comprehensive income (loss)	17.5	(10.3)	72.2	(46)
Comprehensive income (loss)	$ 29	$ 23.1	$ 126.9	$ (8.7)

Condensed Consolidated Statem_3

Condensed Consolidated Statement of Stockholders' Equity Statement - USD ($) shares in Millions, $ in Millions	Total	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	AOCI Attributable to Parent [Member]	Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect of change in accounting for equity securities and other invested assets and reclassification of stranded tax effects as of January 1, 2018	$ (63.9)
Balance at beginning of year (shares) at Dec. 31, 2017		(49.2)	(6.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares (shares)		0.6
Balance at end of year (shares) at Sep. 30, 2018		(49.8)	(6.8)
Balance at beginning of year at Dec. 31, 2017		$ (123)	$ (116.8)	$ (171.8)	$ (3.8)	$ (653.2)
Balance at end of year at Sep. 30, 2018	(831.6)	(124.5)	(117)	(188.6)	106.1	(741.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares		1.5		10.1
Shares acquired on stock award exercises and vested restricted shares			$ (0.2)
Stock awards granted				6.7
Change in net unrealized holding (losses) gains, net of tax	(50)				(50)
Change in unrecognized benefit plan obligations, net of tax and reclassification adjustments	4				4
Net income (loss)	37.3					37.3
Cash dividends paid		$ (12.8)
Balance at beginning of year (shares) at Jun. 30, 2018		(49.7)	(6.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares (shares)		0.1
Balance at end of year (shares) at Sep. 30, 2018		(49.8)	(6.8)
Balance at beginning of year at Jun. 30, 2018		$ (124.1)	$ (116.9)	(184.8)	95.8	(712.3)
Balance at end of year at Sep. 30, 2018	(831.6)	(124.5)	(117)	(188.6)	106.1	(741.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares		0.4		2
Shares acquired on stock award exercises and vested restricted shares			$ (0.1)
Stock awards granted				1.8
Change in net unrealized holding (losses) gains, net of tax	(11.6)				(11.6)
Change in unrecognized benefit plan obligations, net of tax and reclassification adjustments	1.3				1.3
Net income (loss)	$ 33.4					33.4
Cash dividends paid		$ (4.1)
Cumulative Effect of change in accounting for equity securities and other invested assets and reclassification of stranded tax effects as of January 1, 2018					(63.9)	63.9
Document Fiscal Year Focus	2019
Balance at beginning of year (shares) at Dec. 31, 2018		(50)	(6.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares (shares)		0.3
Balance at end of year (shares) at Sep. 30, 2019		(50.3)	(6.8)
Balance at beginning of year at Dec. 31, 2018	$ (818.5)	$ (125)	$ (117)	(194.2)	96.4	(712.7)
Balance at end of year at Sep. 30, 2019	(943.7)	(125.8)	(117.5)	(205.2)	24.2	(754.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares		0.8		4
Shares acquired on stock award exercises and vested restricted shares			$ (0.5)
Stock awards granted				7
Change in net unrealized holding (losses) gains, net of tax	70.3				70.3
Change in unrecognized benefit plan obligations, net of tax and reclassification adjustments	1.9				1.9
Net income (loss)	54.7					54.7
Cash dividends paid		$ (13)
Balance at beginning of year (shares) at Jun. 30, 2019		(50.3)	(6.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares (shares)		0
Balance at end of year (shares) at Sep. 30, 2019		(50.3)	(6.8)
Balance at beginning of year at Jun. 30, 2019		$ (125.7)	$ (117.5)	(202.5)	41.7	(747.2)
Balance at end of year at Sep. 30, 2019	(943.7)	(125.8)	(117.5)	(205.2)	24.2	(754.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares		0.1		0.7
Shares acquired on stock award exercises and vested restricted shares			$ 0
Stock awards granted				$ 2
Change in net unrealized holding (losses) gains, net of tax	16.9				16.9
Change in unrecognized benefit plan obligations, net of tax and reclassification adjustments	0.6				0.6
Net income (loss)	$ 11.5					11.5
Cash dividends paid		$ (4.3)
Cumulative Effect of change in accounting for equity securities and other invested assets and reclassification of stranded tax effects as of January 1, 2018					$ 0	$ 0

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities:
Net income	$ 54.7	$ 37.3
Adjustments to reconcile net income to net cash (used in) provided by operating activities:
Depreciation and amortization, net	6.2	6.7
Share-based compensation	7	5.7
Net investment gain	(50.2)	(18.2)
Changes in operating assets and liabilities:
Deferred policy acquisition costs	(12.4)	5.8
Accrued investment income and other assets	(2.3)	(3)
Postretirement and pension benefits	(12.2)	(16.3)
Other liabilities and due to/from affiliates, net	(2.6)	(2.3)
Reinsurance recoverable on losses and loss expenses payable and prepaid reinsurance premiums	(55)	19
Losses and loss expenses payable	(54.1)	(56.9)
Unearned premiums	65	(16.2)
Excess Tax Benefit from Share-based Compensation, Operating Activities	(0.7)	0
Federal income taxes	12.7	8.1
Net cash used in operating activities	(43.9)	(30.3)
Cash flows from investing activities:
Purchases of fixed maturities available-for-sale	(459.9)	(267)
Purchases of equity securities	(48.9)	(82.2)
Purchases of other invested assets	(12.9)	(1.1)
Maturities, calls and pay downs of fixed maturities available-for-sale	267.1	180.4
Sales of fixed maturities available-for-sale	248.7	69.7
Sales of equity securities	34.4	89.3
Sales of other invested assets	1	0.9
Proceeds from Sale of Property, Plant, and Equipment	1.6	0
Net cash provided by (used in) investing activities	31.1	(10)
Cash flows from financing activities:
Proceeds from issuance of common stock	4.8	11.7
Payments to acquire treasury stock	(0.5)	(0.2)
Payment of dividends	(13)	(12.8)
Payment for Debt Extinguishment or Debt Prepayment Cost	0	(0.4)
Net cash used in financing activities	(8.7)	(1.7)
Net decrease in cash and cash equivalents	(21.5)	(42)
Cash and cash equivalents at beginning of period	59.8	91.5
Cash and cash equivalents at end of period	38.3	49.5
Supplemental disclosures:
Interest Paid, Excluding Capitalized Interest, Operating Activities	$ 3.5	$ 4.5

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement of Cash Flows [Abstract]
Interest Expense Debt To Affiliates	$ 0.2	$ 0.2	$ 0.7	$ 0.7

Basis of Presentation

Basis of Presentation	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements of State Auto Financial Corporation and Subsidiaries (“State Auto Financial” or the “Company”) have been prepared in accordance with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by U.S. generally accepted accounting principles (“GAAP”) for complete financial statements. In the opinion of the Company, all adjustments (consisting of normal, recurring accruals) considered necessary for a fair presentation have been included. Operating results for the three and nine months ended September 30, 2019 , are not necessarily indicative of the results that may be expected for the year ending December 31, 2019 . The balance sheet at December 31, 2018 , has been derived from the audited financial statements at that date, but does not include all of the information and footnotes required by GAAP for complete financial statements. For further information, refer to the consolidated financial statements and footnotes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018 (the “ 2018 Form 10-K”). Capitalized terms used herein and not otherwise defined shall have the meaning ascribed to them in the 2018 Form 10-K. Revisions of Previously Issued Financial Statements Revisions to certain line items in the consolidated statements of comprehensive income and consolidated statements of cash flows for the three and nine months ended September 30, 2018 , were affected by revisions of previously issued financial statements. All such changes to the consolidated statements of cash flows were included within cash flows from operating activities and all related changes in the consolidated statements of comprehensive income were isolated to unrecognized benefit plan obligations. The basis of these revisions were described in Note 2 to our Consolidated Financial Statements set forth in Part II, Item 8, "Financial Statements and Supplementary Data" included in the 2018 Form 10-K. Adoption of Recent Accounting Pronouncements Leases In February 2016, the FASB issued ASU 2016-02, "Leases (Topic 842)" that amended previous guidance on lease accounting. The new guidance requires the recognition of lease assets and lease liabilities by lessees for those leases classified as operating leases under previous GAAP. The guidance became effective beginning January 1, 2019 and it did not have a material impact on the Company’s results of operations, consolidated financial position or cash flows. The Company has elected the practical expedients contained in ASC 842-10-65-1(f) and therefore did not reassess the lease classification of its existing leases. Pending Adoption of Recent Accounting Pronouncements For information regarding other accounting pronouncements that the Company has not yet adopted, see the “Pending Adoption of Recent Accounting Pronouncements” section of Note 1 of the Notes to Consolidated Financial Statements in the 2018 Form 10-K.

Investments

Investments	9 Months Ended
	Sep. 30, 2019
Investments, Debt and Equity Securities [Abstract]
Investments	Investments The following tables set forth the cost or amortized cost and fair value of investments by lot at September 30, 2019 and December 31, 2018 : ($ millions) Cost or amortized cost Gross unrealized holding gains Gross unrealized holding losses Fair value September 30, 2019 Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 516.4 $ 14.8 $ (1.2 ) $ 530.0 Obligations of states and political subdivisions 415.3 21.8 — 437.1 Corporate securities 492.3 10.9 (1.1 ) 502.1 U.S. government agencies mortgage-backed securities 705.0 18.2 (3.1 ) 720.1 Total available-for-sale fixed maturities $ 2,129.0 $ 65.7 $ (5.4 ) $ 2,189.3 ($ millions) Cost or amortized cost Gross unrealized holding gains Gross unrealized holding losses Fair value December 31, 2018 Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 438.4 $ 3.2 $ (9.2 ) $ 432.4 Obligations of states and political subdivisions 408.2 7.3 (0.9 ) 414.6 Corporate securities 551.7 0.6 (11.7 ) 540.6 U.S. government agencies mortgage-backed securities 789.9 3.3 (21.3 ) 771.9 Total available-for-sale fixed maturities $ 2,188.2 $ 14.4 $ (43.1 ) $ 2,159.5 The following tables set forth the Company’s gross unrealized losses and fair value on its investments by lot, aggregated by investment category and length of time for individual securities that have been in a continuous unrealized loss position at September 30, 2019 and December 31, 2018 : ($ millions, except # of positions) Less than 12 months 12 months or more Total Fair value Unrealized losses Number of positions Fair value Unrealized losses Number of positions Fair value Unrealized losses Number of positions September 30, 2019 Fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 41.1 $ (0.1 ) 9 $ 184.5 $ (1.1 ) 16 $ 225.6 $ (1.2 ) 25 Obligations of states and political subdivisions — — — 4.1 — 1 4.1 — 1 Corporate securities 20.3 (0.3 ) 2 56.9 $ (0.8 ) 9 77.2 $ (1.1 ) 11 U.S. government agencies mortgage-backed securities 50.9 (0.3 ) 7 161.1 (2.8 ) 35 212.0 (3.1 ) 42 Total temporarily impaired securities $ 112.3 $ (0.7 ) 18 $ 406.6 $ (4.7 ) 61 $ 518.9 $ (5.4 ) 79 ($ millions, except # of positions) Less than 12 months 12 months or more Total Fair value Unrealized losses Number of positions Fair value Unrealized losses Number of positions Fair value Unrealized losses Number of positions December 31, 2018 Fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 83.1 $ (1.8 ) 7 $ 259.6 $ (7.4 ) 35 $ 342.7 $ (9.2 ) 42 Obligations of states and political subdivisions 63.6 (0.5 ) 7 39.6 (0.4 ) 8 103.2 (0.9 ) 15 Corporate securities 244.0 (3.0 ) 31 189.5 (8.7 ) 30 433.5 (11.7 ) 61 U.S. government agencies mortgage-backed securities 169.5 (2.8 ) 18 385.5 (18.5 ) 70 555.0 (21.3 ) 88 Total temporarily impaired securities $ 560.2 $ (8.1 ) 63 $ 874.2 $ (35.0 ) 143 $ 1,434.4 $ (43.1 ) 206 The Company reviewed its investments at September 30, 2019 , and determined that no other-than-temporary impairment ("OTTI") existed in the gross unrealized holding losses. The Company regularly monitors its available-for-sale investments that have fair values less than cost or amortized cost for signs of other-than-temporary impairment, an assessment that requires significant management judgment regarding the evidence known. Such judgments could change in the future as more information becomes known, which could negatively impact the amounts reported. Among the factors that management considers for fixed maturity securities are the financial condition of the issuer including receipt of scheduled principal and interest cash flows, and intent to sell, including if it is more likely than not that the Company will be required to sell the investments before recovery. When a fixed maturity has been determined to have an other-than-temporary impairment, the impairment charge is separated into an amount representing the credit loss, which is recognized in earnings as a realized loss, and the amount related to non-credit factors, which is recognized in accumulated other comprehensive income. Future increases or decreases in fair value, if not other-than-temporary, are included in accumulated other comprehensive income. The following table sets forth the amortized cost and fair value of available-for-sale fixed maturities by contractual maturity at September 30, 2019 : ($ millions) Amortized cost Fair value Due in 1 year or less $ 55.7 $ 56.6 Due after 1 year through 5 years 562.7 569.4 Due after 5 years through 10 years 239.9 249.7 Due after 10 years 565.7 593.5 U.S. government agencies mortgage-backed securities 705.0 720.1 Total $ 2,129.0 $ 2,189.3 Expected maturities may differ from contractual maturities because issuers may have the right to call or prepay the obligations with or without call or prepayment penalties. At September 30, 2019 , State Auto P&C had U.S. government agencies mortgage-backed fixed maturity securities, with a carrying value of approximately $106.5 million , that were pledged as collateral for the FHLB Loans (as defined in Note 3). In accordance with the terms of the FHLB Loans, State Auto P&C retains all rights regarding these pledged securities. At September 30, 2019 , State Auto P&C had fixed maturities with fair values of approximately $23.2 million pledged as collateral for the performance obligations under its reinsurance agreement with Home State County Mutual Insurance Company. In accordance with the terms of the trust agreement, State Auto P&C retains all rights regarding these securities, which are included in the “U.S. treasury securities and obligations of U.S. government agencies” classification of the Company’s fixed maturity securities portfolio. Fixed maturities with fair values of $9.3 million and $8.9 million were on deposit with insurance regulators as required by law at September 30, 2019 , and December 31, 2018 , respectively. The Company retains all rights regarding these securities. The following table sets forth the components of net investment income for the three and nine months ended September 30, 2019 and 2018 : ($ millions) Three months ended September 30 Nine months ended September 30 2019 2018 2019 2018 Fixed maturities $ 15.3 $ 16.4 $ 47.7 $ 49.4 Equity securities 3.0 3.0 8.9 8.6 Cash and cash equivalents, and other 1.1 1.7 4.2 5.2 Investment income 19.4 21.1 60.8 63.2 Investment expenses 0.1 0.3 0.4 1.0 Net investment income $ 19.3 $ 20.8 $ 60.4 $ 62.2 The Company’s current investment strategy does not rely on the use of derivative financial instruments. Proceeds on sales of investments were $284.1 million and $159.9 million for the nine months ended September 30, 2019 , and 2018 , respectively. The following table sets forth the realized and unrealized holding gains (losses) on the Company’s investment portfolio for the three and nine months ended September 30, 2019 and 2018 : ($ millions) Three months ended September 30 Nine months ended September 30 2019 2018 2019 2018 Investment gains (losses), net: Fixed maturities: Realized gains on sales of securities 1.2 — 2.8 1.7 Net gains on fixed maturities 1.2 — 2.8 1.7 Equity securities: Realized (losses) gains on sales of securities, net (1.8 ) 1.0 (2.5 ) 5.4 Unrealized (losses) gains on securities still held, net (4.1 ) 16.4 46.4 12.8 Net (losses) gains on equity securities (5.9 ) 17.4 43.9 18.2 Other invested assets: Unrealized (losses) gains on securities still held, net (0.3 ) 0.4 4.8 (1.7 ) Net (losses) gains on other invested assets (0.3 ) 0.4 4.8 (1.7 ) Other net realized loss — — (1.3 ) — Net (losses) gains on investments $ (5.0 ) $ 17.8 $ 50.2 $ 18.2 Change in unrealized holding gains (losses), net of tax: Fixed maturities $ 21.4 $ (14.7 ) $ 89.0 $ (63.3 ) Deferred federal income tax (liability) benefit (4.5 ) 3.1 (18.7 ) 13.3 Change in net unrealized holding gains (losses), net of tax $ 16.9 $ (11.6 ) $ 70.3 $ (50.0 )

Fair Value of Financial Instrum

Fair Value of Financial Instruments	9 Months Ended
	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	Fair Value of Financial Instruments Below is the fair value hierarchy that categorizes into three levels the inputs to valuation techniques that are used to measure fair value: • Level 1 includes observable inputs which reflect quoted prices for identical assets or liabilities in active markets at the measurement date. • Level 2 includes observable inputs for assets or liabilities other than quoted prices included in Level 1, and it includes valuation techniques which use prices for similar assets and liabilities. • Level 3 includes unobservable inputs which reflect the reporting entity’s estimates of the assumptions that market participants would use in pricing the asset or liability (including assumptions about risk). The Company utilizes a nationally recognized third party pricing service to estimate the majority of its investment portfolio’s fair value. The Company obtains one price per security and the processes and control procedures employed by the Company are designed to ensure the value is accurately recorded on an unadjusted basis. Through discussions with the pricing service, the Company gains an understanding of the methodologies used to price the different types of securities, that the data and the valuation methods utilized are appropriate and consistently applied, and that the assumptions are reasonable and representative of fair value. To validate the reasonableness of the valuations obtained from the pricing service, the Company compares to fair value pricing information gathered from other independent pricing sources. At September 30, 2019 , and December 31, 2018 , the Company did not adjust any of the prices received from the pricing service. Fixed Maturities The Company utilizes a nationally recognized third party pricing service to estimate fair value measurements for the majority of its fixed maturities. The fair value estimate of the Company’s fixed maturity investments are determined by evaluations that are based on observable market information rather than market quotes. Inputs to the evaluations include, but are not limited to, market prices from recently completed transactions and transactions of comparable securities, interest rate yield curves, credit spreads, and other market-observable information. The fixed maturity portfolio pricing obtained from the pricing service is reviewed for reasonableness. The Company regularly selects a sample of security prices which are compared to one or more alternative pricing sources for reasonableness. Any significant discrepancies with the pricing are returned to the pricing service for further explanation and, if necessary, adjustments are made. To date, the Company has not identified any significant discrepancies in the pricing provided by its third party pricing service. Investments valued using these inputs include U.S. treasury securities and obligations of U.S. government agencies, obligations of states and political subdivisions, corporate securities (except for a security discussed below), and U.S. government agencies' mortgage-backed securities. All unadjusted estimates of fair value for fixed maturities priced by the pricing service are included in the amounts disclosed in Level 2 of the hierarchy. If market inputs are unavailable, then no fair value is provided by the pricing service. For these securities, fair value is determined either by requesting brokers who are knowledgeable about these securities to provide a quote; or the Company internally determines the fair values by employing widely accepted pricing valuation models, and depending on the level of observable market inputs, renders the fair value estimate as Level 2 or Level 3. Transfers between level categorizations may occur due to changes in the availability of market observable inputs. Transfers in and out of level categorizations are reported as having occurred at the beginning of the quarter in which the transfer occurred. Equities The fair value of each equity security is based on an observable market price for an identical asset in an active market and is priced by the same pricing service discussed above. All equity securities are recorded using unadjusted market prices and have been disclosed in Level 1. Other Invested Assets Included in other invested assets is one international fund (“the fund”) that invests in equity securities of foreign issuers and is managed by a third party investment manager. The fund had a fair value of $51.7 million and $38.5 million at September 30, 2019 , and December 31, 2018 , respectively, which was determined using the fund’s net asset value. The Company employs procedures to assess the reasonableness of the fair value of the fund, including obtaining and reviewing the fund’s audited financial statements. There are no unfunded commitments related to the fund. The Company may not sell its investment in the fund; however, the Company may redeem all or a portion of its investment in the fund at net asset value per share with the appropriate prior written notice. In accordance with Accounting Standard Codification 820-10, this investment is measured at fair value using the net asset value per share practical expedient and has not been classified in the fair value hierarchy. Fair values presented here are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the condensed consolidated balance sheets. The remainder of the Company’s other invested assets consist primarily of holdings in publicly-traded mutual funds. The Company believes that its prices for these publicly-traded mutual funds based on an observable market price for an identical asset in an active market reflect their fair values and consequently these securities have been disclosed in Level 1. The following tables set forth the Company’s investments within the fair value hierarchy at September 30, 2019 and December 31, 2018 : ($ millions) Total Level 1 Level 2 September 30, 2019 Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 530.0 $ — $ 530.0 Obligations of states and political subdivisions 437.1 — 437.1 Corporate securities 502.1 — 502.1 U.S. government agencies mortgage-backed securities 720.1 — 720.1 Total available-for-sale fixed maturities 2,189.3 — 2,189.3 Equity securities: Large-cap securities 99.1 99.1 — Mutual and exchange traded funds 274.2 274.2 — Total equity securities 373.3 373.3 — Other invested assets 12.9 12.9 — Total investments $ 2,575.5 $ 386.2 $ 2,189.3 ($ millions) Total Level 1 Level 2 December 31, 2018 Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 432.4 $ — $ 432.4 Obligations of states and political subdivisions 414.6 — 414.6 Corporate securities 540.6 — 540.6 U.S. government agencies mortgage-backed securities 771.9 — 771.9 Total available-for-sale fixed maturities 2,159.5 — 2,159.5 Equity securities: Large-cap securities 77.2 77.2 — Mutual and exchange traded funds 237.8 237.8 — Total equity securities 315.0 315.0 — Other invested assets 10.3 10.3 — Total investments $ 2,484.8 $ 325.3 $ 2,159.5 The following sections describe the valuation methods used by the Company for each type of financial instrument it holds that is not measured at fair value but for which fair value is disclosed: Financial Instruments Disclosed, But Not Carried, At Fair Value Other Invested Assets, at Cost Included in other invested assets, at cost are common stock of the Federal Home Loan Bank of Cincinnati (the "FHLB") and the Trust Securities. The Trust Securities and FHLB common stock are carried at cost, which approximates fair value. The fair value of the FHLB common stock at September 30, 2019 , was $6.0 million and the fair value of the Trust Securities was $0.5 million . The investments have been placed in Level 3 of the fair value hierarchy. Notes Receivable from Affiliate In May 2009, the Company entered into two separate credit agreements with State Automobile Mutual Insurance Company (“State Auto Mutual") pursuant to which it loaned State Auto Mutual a total of $70.0 million at an interest rate of 7.00% . In May 2019, the Company refinanced the two credit agreements with State Auto Mutual at an interest rate of 4.05% , with principal payable in May 2029. The Company estimates the fair value of the notes receivable from affiliate using market quotations for U.S. treasury securities with similar maturity dates and applies an appropriate credit spread. Consequently this has been placed in Level 2 of the fair value hierarchy. ($ millions, except interest rates) September 30, 2019 December 31, 2018 Carrying value Fair value Interest rate Carrying value Fair value Interest rate Notes receivable from affiliate, May 2009 $ — $ — — % $ 70.0 $ 71.1 7.00 % Notes receivable from affiliate, May 2019 $ 70.0 $ 76.8 4.05 % $ — $ — — % Notes Payable Included in notes payable are the FHLB Loans and Subordinated Debentures. The Company estimates the fair value of the FHLB Loans by discounting cash flows using a borrowing rate currently available to the Company for loans with similar terms. The FHLB Loans have been placed in Level 3 of the fair value hierarchy. The carrying amount of the Subordinated Debentures approximates its fair value as the interest rate adjusts quarterly and has been disclosed in Level 3. ($ millions, except interest rates) September 30, 2019 December 31, 2018 Carrying value Fair Value Interest rate Carrying value Fair value Interest rate FHLB Loan due 2021: issued $21.5, September 2016 with fixed interest $ 21.5 $ 21.5 1.73 % $ 21.5 $ 20.9 1.73 % FHLB Loan due 2033: issued $85.0, May 2018 with fixed interest 85.3 100.1 3.96 % 85.3 89.0 3.96 % Affiliate Subordinated Debentures due 2033: issued $15.5, May 2003 with variable interest 15.2 15.2 6.33 % 15.2 15.2 6.94 % Total notes payable $ 122.0 $ 136.8 $ 122.0 $ 125.1

Losses and Loss Expenses Payabl

Losses and Loss Expenses Payable Losses and Loss Expenses Payable	9 Months Ended
	Sep. 30, 2019
Losses and Loss Expenses Payable [Abstract]
Liability for Future Policy Benefits and Unpaid Claims Disclosure [Text Block]	. Losses and Loss Expenses Payable The following table sets forth the activity in the liability for losses and loss expenses for the nine months ended September 30, 2019 and 2018 : ($ millions) 2019 2018 Losses and loss expenses payable, at beginning of period $ 1,146.8 $ 1,255.6 Less: reinsurance recoverable on losses and loss expenses payable 5.5 3.1 Net balance at beginning of period 1,141.3 1,252.5 Incurred related to: Current year 692.7 678.7 Prior years (55.1 ) (57.6 ) Total incurred 637.6 621.1 Paid related to: Current year 366.4 314.1 Prior years 327.0 365.8 Total paid 693.4 679.9 Net balance at end of period 1,085.5 1,193.7 Plus: reinsurance recoverable on losses and loss expenses payable 7.2 5.0 Losses and loss expenses payable, at end of period $ 1,092.7 $ 1,198.7 The Company recorded favorable development related to prior years’ loss and loss expense reserves for the nine months ended September 30, 2019 , of $55.1 million compared to favorable development of $57.6 million for the same 2018 period. Favorable development of prior accident years' non-catastrophe loss and ALAE reserves for the nine months ended September 30, 2019 was $54.1 million . In the personal insurance segment, personal auto contributed $11.0 million of favorable development. In the commercial insurance segment, all lines contributed favorable development, with workers' compensation, small commercial package, and middle market commercial contributing $13.4 million , $11.8 million , and $7.2 million , respectively. For the nine months ended September 30, 2018 , favorable development of prior accident years' non-catastrophe loss and ALAE reserves was primarily due to $56.4 million of favorable development in the personal and commercial insurance segments. In the personal insurance segment, personal auto contributed $18.5 million of favorable development and homeowners contributed $7.2 million of favorable development. In the commercial insurance segment all lines contributed favorable development, with workers' compensation, small commercial package and commercial auto contributing $8.4 million , $6.5 million , and $5.7 million , respectively. Slightly offsetting the favorable development was adverse development in the specialty insurance segment of $4.1 million . The specialty insurance segment was impacted by $3.4 million and $0.9 million of adverse development in E&S casualty and programs, respectively.

Reinsurance

Reinsurance	9 Months Ended
	Sep. 30, 2019
Insurance [Abstract]
Reinsurance	Reinsurance The insurance subsidiaries of State Auto Financial, including State Auto P&C, Milbank and SA Ohio (collectively referred to as the “STFC Pooled Companies”) participate in a quota share reinsurance pooling arrangement (“the Pooling Arrangement”) with State Auto Mutual and its subsidiaries and affiliates (collectively referred to as the “Mutual Pooled Companies”). The following table sets forth a summary of the Company’s external reinsurance transactions, as well as reinsurance transactions with State Auto Mutual under the Pooling Arrangement, for the three and nine months ended September 30, 2019 and 2018 : ($ millions) Three months ended September 30 Nine months ended September 30 2019 2018 2019 2018 Premiums earned: Assumed from external insurers and reinsurers $ 21.0 $ 17.3 $ 59.3 $ 41.9 Assumed under Pooling Arrangement 319.6 306.8 930.0 929.2 Ceded to external insurers and reinsurers (6.6 ) (5.9 ) (18.8 ) (16.7 ) Ceded under Pooling Arrangement (263.9 ) (234.9 ) (761.5 ) (678.1 ) Net assumed premiums earned $ 70.1 $ 83.3 $ 209.0 $ 276.3 Losses and loss expenses incurred: Assumed from external insurers and reinsurers $ 14.6 $ 10.9 $ 45.6 $ 34.2 Assumed under Pooling Arrangement 209.3 191.4 639.4 622.3 Ceded to external insurers and reinsurers (0.6 ) (1.9 ) (6.2 ) (3.4 ) Ceded under Pooling Arrangement (185.1 ) (148.4 ) (514.3 ) (486.0 ) Net assumed losses and loss expenses incurred $ 38.2 $ 52.0 $ 164.5 $ 167.1

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The following table sets forth the reconciliation between actual federal income tax expense and the amount computed at the indicated statutory rate for the three and nine months ended September 30, 2019 and 2018 : ($ millions) Three months ended September 30 Nine months ended September 30 2019 2018 2019 2018 Amount at statutory rate $ 2.7 21.0 % $ 8.6 21.0 % $ 14.0 21.0 % $ 9.5 21.0 % Tax-exempt interest and dividends received deduction (0.7 ) (5.3 ) (0.5 ) (1.3 ) (2.1 ) (3.1 ) (1.7 ) (3.8 ) Other, net (0.8 ) (6.3 ) (0.5 ) (1.1 ) 0.1 — 0.3 0.6 Federal income tax expense 1.2 9.4 % 7.6 18.6 % 12.0 17.9 % $ 8.1 17.8 %

Pension and Postretirement Bene

Pension and Postretirement Benefit Plans	9 Months Ended
	Sep. 30, 2019
Retirement Benefits [Abstract]
Pension and Postretirement Benefit Plans	Pension and Postretirement Benefit Plans The following table sets forth information regarding the Company’s share of pension and postretirement benefit plans’ components of net periodic cost for the three and nine months ended September 30, 2019 and 2018 : ($ millions) Pension Postretirement Pension Postretirement Three months ended September 30 Nine months ended September 30 2019 2018 2019 2018 2019 2018 2019 2018 Service cost $ 0.8 $ 1.2 $ — $ — $ 2.8 $ 3.8 $ — $ — Interest cost 2.9 2.7 0.2 0.2 8.6 8.0 0.5 0.5 Expected return on plan assets (4.2 ) (4.5 ) — — (12.5 ) (13.5 ) — — Amortization of: Negative prior service cost — — (1.4 ) (1.4 ) — — (4.1 ) (4.1 ) Net actuarial loss 1.5 2.1 0.1 0.1 4.5 6.2 0.2 0.2 Net periodic cost (benefit) $ 1.0 $ 1.5 $ (1.1 ) $ (1.1 ) $ 3.4 $ 4.5 $ (3.4 ) $ (3.4 ) The Company contributed $10.0 million to its pension plan for the nine months ended September 30, 2019 .

Other Comprehensive Income and

Other Comprehensive Income and Accumulated Other Comprehensive Income	9 Months Ended
	Sep. 30, 2019
Equity [Abstract]
Other Comprehensive Income and Accumulated Other Comprehensive Income	Other Comprehensive Income and Accumulated Other Comprehensive Loss The following tables set forth the changes in the Company’s accumulated other comprehensive (loss) income ("AOC(L)I"), net of tax, for the three and nine months ended September 30, 2019 and 2018 : ($ millions) Unrealized Gains and Losses on Available-for-Sale Securities Benefit Plan Items Total Beginning balance at July 1, 2019 $ 33.2 $ (74.9 ) $ (41.7 ) Other comprehensive income before reclassifications 17.8 — 17.8 Amounts reclassified from AOCI (a) (0.9 ) 0.6 (0.3 ) Net current period other comprehensive income 16.9 0.6 17.5 Ending balance at September 30, 2019 $ 50.1 $ (74.3 ) $ (24.2 ) Beginning balance at July 1, 2018 $ (20.3 ) $ (75.5 ) $ (95.8 ) Other comprehensive loss before reclassifications (11.6 ) — (11.6 ) Amounts reclassified from AOCI (a) — 1.3 1.3 Net current period other comprehensive (loss) income (11.6 ) 1.3 (10.3 ) Ending balance at September 30, 2018 $ (31.9 ) $ (74.2 ) $ (106.1 ) (a) See separate table below for details about these reclassifications ($ millions) Unrealized Gains and Losses on Available-for-Sale Securities Benefit Plan Items Total Beginning balance at January 1, 2019 $ (20.2 ) $ (76.2 ) $ (96.4 ) Other comprehensive income before reclassifications 72.5 — 72.5 Amounts reclassified from AOCI (a) (2.2 ) 1.9 (0.3 ) Net current period other comprehensive income 70.3 1.9 72.2 Ending balance at September 30, 2019 $ 50.1 $ (74.3 ) $ (24.2 ) Beginning balance at January 1, 2018 $ 66.0 $ (62.2 ) $ 3.8 Cumulative effect of change in accounting for equity securities and other invested assets and reclassification of stranded tax effects as of January 1, 2018 (47.9 ) (16.0 ) (63.9 ) Other comprehensive loss before reclassifications (48.7 ) — (48.7 ) Amounts reclassified from AOCI (a) (1.3 ) 4.0 2.7 Net current period other comprehensive (loss) income (50.0 ) 4.0 (46.0 ) Ending balance at September 30, 2018 $ (31.9 ) $ (74.2 ) $ (106.1 ) (a) See separate table below for details about these reclassifications The following tables set forth the reclassifications out of accumulated other comprehensive income, by component, to the Company’s condensed consolidated statement of income for the three and nine months ended September 30, 2019 and 2018 : ($ millions) Details about Accumulated Other Three months ended September 30 Affected line item in the Condensed Comprehensive Income Components Consolidated Statements of Income 2019 2018 Unrealized gains on available-for-sale fixed maturity investments $ 1.2 $ — Realized gains on sale of securities 1.2 — Total before tax (0.3 ) — Tax expense 0.9 — Net of tax Amortization of benefit plan items Negative prior service cost 1.6 1.6 (b) Net actuarial loss (2.4 ) (3.3 ) (b) (0.8 ) (1.7 ) Total before tax 0.2 0.4 Tax benefit (0.6 ) (1.3 ) Net of tax Total reclassifications for the period $ 0.3 $ (1.3 ) (b) These accumulated other comprehensive income components are included in the computation of net periodic pension cost (see pension and postretirement benefit plans footnote for additional details). ($ millions) Details about Accumulated Other Nine months ended September 30 Affected line item in the Condensed Comprehensive Income Components Consolidated Statements of Income 2019 2018 Unrealized gains on available-for-sale fixed maturity investments $ 2.8 $ 1.7 Realized gain on sale of securities 2.8 1.7 Total before tax (0.6 ) (0.4 ) Tax expense 2.2 1.3 Net of tax Amortization of benefit plan items Negative prior service cost 4.8 4.8 (b) Net actuarial loss (7.2 ) (9.9 ) (b) (2.4 ) (5.1 ) Total before tax 0.5 1.1 Tax benefit (1.9 ) (4.0 ) Net of tax Total reclassifications for the period $ 0.3 $ (2.7 ) (b) These accumulated other comprehensive income components are included in the computation of net periodic pension cost (see pension and postretirement benefit plans footnote for additional details).

Earnings per Common Share

Earnings per Common Share	9 Months Ended
	Sep. 30, 2019
Earnings Per Share [Abstract]
Earnings (Loss) per Common Share	Net Earnings per Common Share The following table sets forth the compilation of basic and diluted (loss) earnings per common share for the three and nine months ended September 30, 2019 and 2018 : ($ and shares in millions, except per share amounts) Three months ended September 30 Nine months ended September 30 2019 2018 2019 2018 Numerator: Net income for basic earnings per common share $ 11.5 $ 33.4 $ 54.7 $ 37.3 Denominator: Weighted average shares for basic (loss) earnings per common share 43.5 43.0 43.4 42.8 Effect of dilutive share-based awards 0.5 0.6 0.6 0.5 Adjusted weighted average shares for diluted net (loss) earnings per common share 44.0 43.6 44.0 43.3 Basic net earnings per common share $ 0.26 $ 0.78 $ 1.26 $ 0.87 Diluted net earnings per common share $ 0.25 $ 0.76 $ 1.25 $ 0.86 The following table sets forth common stock options, stock awards and restricted share units ("RSU award") of the Company that were not included in the computation of diluted earnings per common share because the exercise price of the options, or awards, was greater than the average market price or their inclusion would have been antidilutive for the three and nine months ended September 30, 2019 and 2018 : (shares in millions) Three months ended September 30 Nine months ended September 30 2019 2018 2019 2018 Total number of antidilutive options and awards — — — 0.1

Segment Information

Segment Information	9 Months Ended
	Sep. 30, 2019
Segment Reporting [Abstract]
Segment Information	Segment Information The Company changed its reportable segments from four to three effective January 1, 2019. The exit from the specialty insurance business resulted in the elimination of specialty insurance as a reportable segment as it no longer is material to the Company's results and is disclosed as "specialty run-off." The three remaining reportable segments are: personal insurance, commercial insurance, and investment operations. The reportable insurance segments are business units managed separately because of the differences in the type of customers they serve, the products they provide or services they offer. The insurance segments market a broad line of property and casualty insurance products throughout the United States through independent insurance agencies, which include retail agents and wholesale brokers. The investment operations segment, managed by Stateco, provides investment services. The Company evaluates the performance of its insurance segments using industry financial measurements based on Statutory Accounting Practices (“SAP”), which include loss and loss adjustment expense ratios, underwriting expense ratios, combined ratios, statutory underwriting gain (loss), net premiums earned and net written premiums. One of the most significant differences between SAP and GAAP is that SAP requires all underwriting expenses to be expensed immediately and not deferred and amortized over the same period the premium is earned. The investment operations segment is evaluated based on investment returns of assets managed by Stateco. Asset information by segment is not reported for the insurance segments because the Company does not produce such information internally. The following table sets forth financial information regarding the Company’s reportable segments and specialty run-off for the three and nine months ended September 30, 2019 and 2018 : ($ millions) Three months ended September 30 Nine months ended September 30 2019 2018 2019 2018 Revenue from external sources: Insurance operations Personal insurance $ 192.7 $ 173.0 $ 562.5 $ 494.2 Commercial insurance 127.0 115.2 361.4 345.7 Specialty run-off (0.1 ) 18.6 6.1 89.3 Total insurance operations 319.6 306.8 930.0 929.2 Investment operations Net investment income 19.3 20.8 60.4 62.2 Net investment (loss) gain (5.0 ) 17.8 50.2 18.2 Total investment operations 14.3 38.6 110.6 80.4 All other 0.6 0.6 1.6 1.8 Total revenue from external sources 334.5 346.0 1,042.2 1,011.4 Intersegment revenue 1.7 1.6 4.9 4.8 Total revenue 336.2 347.6 1,047.1 1,016.2 Reconciling items: Eliminate intersegment revenue (1.7 ) (1.6 ) (4.9 ) (4.8 ) Total consolidated revenues $ 334.5 $ 346.0 $ 1,042.2 $ 1,011.4 Segment (loss) income before federal income tax: Insurance operations SAP underwriting (loss) gain Personal insurance $ (6.3 ) $ 6.9 $ (32.0 ) $ (4.6 ) Commercial insurance 1.2 (5.2 ) (17.1 ) (22.3 ) Specialty run-off (0.6 ) 1.9 (1.3 ) 4.5 Total insurance operations (5.7 ) 3.6 (50.4 ) (22.4 ) Investment operations Net investment income 19.3 20.8 60.4 62.2 Net investment (loss) gain (5.0 ) 17.8 50.2 18.2 Total investment operations 14.3 38.6 110.6 80.4 All other — 0.1 0.2 0.3 Total segment income before reconciling items 8.6 42.3 60.4 58.3 Reconciling items: GAAP expense adjustments 7.2 0.8 17.3 (2.6 ) Interest expense on corporate debt (1.2 ) (1.2 ) (3.7 ) (4.5 ) Corporate expenses (1.9 ) (0.9 ) (7.3 ) (5.8 ) Total reconciling items 4.1 (1.3 ) 6.3 (12.9 ) Total consolidated income before federal income tax $ 12.7 $ 41.0 $ 66.7 $ 45.4 Investable assets attributable to the Company’s investment operations segment totaled $2,742.0 million and $2,658.7 million at September 30, 2019 , and December 31, 2018 , respectively.

Contingencies and Litigation

Contingencies and Litigation	9 Months Ended
	Sep. 30, 2019
Commitments and Contingencies Disclosure [Abstract]
Contingencies and Litigation	Contingencies and Litigation In accordance with the Contingencies Topic of the FASB's Accounting Standards Codification, the Company accrues for a litigation-related liability when it is probable that such a liability has been incurred and the amount can be reasonably estimated. The Company reviews all litigation on an ongoing basis when making accrual and disclosure decisions. For certain legal proceedings, the Company cannot reasonably estimate a loss or a range of loss, if any, particularly for proceedings that are in their early stages of development or where the plaintiffs seek indeterminate damages. Various factors, including, but not limited to, the outcome of potentially lengthy discovery and the resolution of important factual questions, may need to be determined before probability can be established or before a loss or range of loss can be reasonably estimated. If the loss contingency in question is not both probable and reasonably estimable, the Company does not establish an accrual and the matter will continue to be monitored for any developments that would make the loss contingency both probable and reasonably estimable. Based on currently available information known to the Company, it believes that its reserves for litigation-related liabilities are reasonable. However, in the event that a legal proceeding results in a substantial judgment against, or settlement by, the Company, there can be no assurance that any resulting liability or financial commitment would not have a material adverse effect on the financial condition, results of operations or cash flows of the consolidated financial statements of the Company. The Company is involved in lawsuits in the ordinary course of its business arising out of or otherwise related to its insurance policies. Additionally, from time to time the Company may be involved in lawsuits, including class actions, in the ordinary course of business but not arising out of or otherwise related to its insurance policies. These lawsuits are in various stages of development. The Company generally will contest these matters vigorously but may pursue settlement if appropriate. Based on currently available information, the Company does not believe it is reasonably possible that any such lawsuit or related lawsuits will be material to its results of operations or have a material adverse effect on its consolidated financial position, results of operations or cash flows. Additionally, the Company may be impacted by adverse regulatory actions and adverse court decisions where insurance coverages are expanded beyond the scope originally contemplated in its insurance policies. The Company believes that the effects, if any, of such regulatory actions and published court decisions are not likely to have a material adverse effect on its consolidated financial position, results of operations or cash flows.

Investments (Tables)

Investments (Tables)	9 Months Ended
	Sep. 30, 2019
Investments, Debt and Equity Securities [Abstract]
Cost or Amortized Cost and Fair Value of Available-for-Sale Securities	The following tables set forth the cost or amortized cost and fair value of investments by lot at September 30, 2019 and December 31, 2018 : ($ millions) Cost or amortized cost Gross unrealized holding gains Gross unrealized holding losses Fair value September 30, 2019 Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 516.4 $ 14.8 $ (1.2 ) $ 530.0 Obligations of states and political subdivisions 415.3 21.8 — 437.1 Corporate securities 492.3 10.9 (1.1 ) 502.1 U.S. government agencies mortgage-backed securities 705.0 18.2 (3.1 ) 720.1 Total available-for-sale fixed maturities $ 2,129.0 $ 65.7 $ (5.4 ) $ 2,189.3 ($ millions) Cost or amortized cost Gross unrealized holding gains Gross unrealized holding losses Fair value December 31, 2018 Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 438.4 $ 3.2 $ (9.2 ) $ 432.4 Obligations of states and political subdivisions 408.2 7.3 (0.9 ) 414.6 Corporate securities 551.7 0.6 (11.7 ) 540.6 U.S. government agencies mortgage-backed securities 789.9 3.3 (21.3 ) 771.9 Total available-for-sale fixed maturities $ 2,188.2 $ 14.4 $ (43.1 ) $ 2,159.5
Gross Unrealized Losses and Fair Value on its Investments	The following tables set forth the Company’s gross unrealized losses and fair value on its investments by lot, aggregated by investment category and length of time for individual securities that have been in a continuous unrealized loss position at September 30, 2019 and December 31, 2018 : ($ millions, except # of positions) Less than 12 months 12 months or more Total Fair value Unrealized losses Number of positions Fair value Unrealized losses Number of positions Fair value Unrealized losses Number of positions September 30, 2019 Fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 41.1 $ (0.1 ) 9 $ 184.5 $ (1.1 ) 16 $ 225.6 $ (1.2 ) 25 Obligations of states and political subdivisions — — — 4.1 — 1 4.1 — 1 Corporate securities 20.3 (0.3 ) 2 56.9 $ (0.8 ) 9 77.2 $ (1.1 ) 11 U.S. government agencies mortgage-backed securities 50.9 (0.3 ) 7 161.1 (2.8 ) 35 212.0 (3.1 ) 42 Total temporarily impaired securities $ 112.3 $ (0.7 ) 18 $ 406.6 $ (4.7 ) 61 $ 518.9 $ (5.4 ) 79 ($ millions, except # of positions) Less than 12 months 12 months or more Total Fair value Unrealized losses Number of positions Fair value Unrealized losses Number of positions Fair value Unrealized losses Number of positions December 31, 2018 Fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 83.1 $ (1.8 ) 7 $ 259.6 $ (7.4 ) 35 $ 342.7 $ (9.2 ) 42 Obligations of states and political subdivisions 63.6 (0.5 ) 7 39.6 (0.4 ) 8 103.2 (0.9 ) 15 Corporate securities 244.0 (3.0 ) 31 189.5 (8.7 ) 30 433.5 (11.7 ) 61 U.S. government agencies mortgage-backed securities 169.5 (2.8 ) 18 385.5 (18.5 ) 70 555.0 (21.3 ) 88 Total temporarily impaired securities $ 560.2 $ (8.1 ) 63 $ 874.2 $ (35.0 ) 143 $ 1,434.4 $ (43.1 ) 206
Amortized Cost and Fair Value of Available-for-Sale Fixed Maturities by Contractual Maturity	The following table sets forth the amortized cost and fair value of available-for-sale fixed maturities by contractual maturity at September 30, 2019 : ($ millions) Amortized cost Fair value Due in 1 year or less $ 55.7 $ 56.6 Due after 1 year through 5 years 562.7 569.4 Due after 5 years through 10 years 239.9 249.7 Due after 10 years 565.7 593.5 U.S. government agencies mortgage-backed securities 705.0 720.1 Total $ 2,129.0 $ 2,189.3
Components of Net Investment Income	The following table sets forth the components of net investment income for the three and nine months ended September 30, 2019 and 2018 : ($ millions) Three months ended September 30 Nine months ended September 30 2019 2018 2019 2018 Fixed maturities $ 15.3 $ 16.4 $ 47.7 $ 49.4 Equity securities 3.0 3.0 8.9 8.6 Cash and cash equivalents, and other 1.1 1.7 4.2 5.2 Investment income 19.4 21.1 60.8 63.2 Investment expenses 0.1 0.3 0.4 1.0 Net investment income $ 19.3 $ 20.8 $ 60.4 $ 62.2
Realized and Unrealized Holding Gains (Losses)	The following table sets forth the realized and unrealized holding gains (losses) on the Company’s investment portfolio for the three and nine months ended September 30, 2019 and 2018 : ($ millions) Three months ended September 30 Nine months ended September 30 2019 2018 2019 2018 Investment gains (losses), net: Fixed maturities: Realized gains on sales of securities 1.2 — 2.8 1.7 Net gains on fixed maturities 1.2 — 2.8 1.7 Equity securities: Realized (losses) gains on sales of securities, net (1.8 ) 1.0 (2.5 ) 5.4 Unrealized (losses) gains on securities still held, net (4.1 ) 16.4 46.4 12.8 Net (losses) gains on equity securities (5.9 ) 17.4 43.9 18.2 Other invested assets: Unrealized (losses) gains on securities still held, net (0.3 ) 0.4 4.8 (1.7 ) Net (losses) gains on other invested assets (0.3 ) 0.4 4.8 (1.7 ) Other net realized loss — — (1.3 ) — Net (losses) gains on investments $ (5.0 ) $ 17.8 $ 50.2 $ 18.2 Change in unrealized holding gains (losses), net of tax: Fixed maturities $ 21.4 $ (14.7 ) $ 89.0 $ (63.3 ) Deferred federal income tax (liability) benefit (4.5 ) 3.1 (18.7 ) 13.3 Change in net unrealized holding gains (losses), net of tax $ 16.9 $ (11.6 ) $ 70.3 $ (50.0 )

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Company's Investments within Fair Value Hierarchy	The following tables set forth the Company’s investments within the fair value hierarchy at September 30, 2019 and December 31, 2018 : ($ millions) Total Level 1 Level 2 September 30, 2019 Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 530.0 $ — $ 530.0 Obligations of states and political subdivisions 437.1 — 437.1 Corporate securities 502.1 — 502.1 U.S. government agencies mortgage-backed securities 720.1 — 720.1 Total available-for-sale fixed maturities 2,189.3 — 2,189.3 Equity securities: Large-cap securities 99.1 99.1 — Mutual and exchange traded funds 274.2 274.2 — Total equity securities 373.3 373.3 — Other invested assets 12.9 12.9 — Total investments $ 2,575.5 $ 386.2 $ 2,189.3 ($ millions) Total Level 1 Level 2 December 31, 2018 Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 432.4 $ — $ 432.4 Obligations of states and political subdivisions 414.6 — 414.6 Corporate securities 540.6 — 540.6 U.S. government agencies mortgage-backed securities 771.9 — 771.9 Total available-for-sale fixed maturities 2,159.5 — 2,159.5 Equity securities: Large-cap securities 77.2 77.2 — Mutual and exchange traded funds 237.8 237.8 — Total equity securities 315.0 315.0 — Other invested assets 10.3 10.3 — Total investments $ 2,484.8 $ 325.3 $ 2,159.5
Company Estimates Receivable from Affiliate using Market Quotations for U.S. Treasury Securities	Consequently this has been placed in Level 2 of the fair value hierarchy. ($ millions, except interest rates) September 30, 2019 December 31, 2018 Carrying value Fair value Interest rate Carrying value Fair value Interest rate Notes receivable from affiliate, May 2009 $ — $ — — % $ 70.0 $ 71.1 7.00 % Notes receivable from affiliate, May 2019 $ 70.0 $ 76.8 4.05 % $ — $ — — %
Included in Notes Payable are Senior Notes and Subordinated Debentures	The carrying amount of the Subordinated Debentures approximates its fair value as the interest rate adjusts quarterly and has been disclosed in Level 3. ($ millions, except interest rates) September 30, 2019 December 31, 2018 Carrying value Fair Value Interest rate Carrying value Fair value Interest rate FHLB Loan due 2021: issued $21.5, September 2016 with fixed interest $ 21.5 $ 21.5 1.73 % $ 21.5 $ 20.9 1.73 % FHLB Loan due 2033: issued $85.0, May 2018 with fixed interest 85.3 100.1 3.96 % 85.3 89.0 3.96 % Affiliate Subordinated Debentures due 2033: issued $15.5, May 2003 with variable interest 15.2 15.2 6.33 % 15.2 15.2 6.94 % Total notes payable $ 122.0 $ 136.8 $ 122.0 $ 125.1

Losses and Loss Expenses Paya_2

Losses and Loss Expenses Payable Losses and Loss Expenses Payable (Tables)	9 Months Ended
	Sep. 30, 2019
Losses and Loss Expenses Payable [Abstract]
Schedule Of Activity In Liability For Unpaid Losses And Loss Adjustment Expenses Table [Table Text Block]	($ millions) 2019 2018 Losses and loss expenses payable, at beginning of period $ 1,146.8 $ 1,255.6 Less: reinsurance recoverable on losses and loss expenses payable 5.5 3.1 Net balance at beginning of period 1,141.3 1,252.5 Incurred related to: Current year 692.7 678.7 Prior years (55.1 ) (57.6 ) Total incurred 637.6 621.1 Paid related to: Current year 366.4 314.1 Prior years 327.0 365.8 Total paid 693.4 679.9 Net balance at end of period 1,085.5 1,193.7 Plus: reinsurance recoverable on losses and loss expenses payable 7.2 5.0 Losses and loss expenses payable, at end of period $ 1,092.7 $ 1,198.7

Reinsurance (Tables)

Reinsurance (Tables)	9 Months Ended
	Sep. 30, 2019
Insurance [Abstract]
Summary of External Reinsurance Transactions with State Auto Mutual Under Pooling Arrangement	The following table sets forth a summary of the Company’s external reinsurance transactions, as well as reinsurance transactions with State Auto Mutual under the Pooling Arrangement, for the three and nine months ended September 30, 2019 and 2018 : ($ millions) Three months ended September 30 Nine months ended September 30 2019 2018 2019 2018 Premiums earned: Assumed from external insurers and reinsurers $ 21.0 $ 17.3 $ 59.3 $ 41.9 Assumed under Pooling Arrangement 319.6 306.8 930.0 929.2 Ceded to external insurers and reinsurers (6.6 ) (5.9 ) (18.8 ) (16.7 ) Ceded under Pooling Arrangement (263.9 ) (234.9 ) (761.5 ) (678.1 ) Net assumed premiums earned $ 70.1 $ 83.3 $ 209.0 $ 276.3 Losses and loss expenses incurred: Assumed from external insurers and reinsurers $ 14.6 $ 10.9 $ 45.6 $ 34.2 Assumed under Pooling Arrangement 209.3 191.4 639.4 622.3 Ceded to external insurers and reinsurers (0.6 ) (1.9 ) (6.2 ) (3.4 ) Ceded under Pooling Arrangement (185.1 ) (148.4 ) (514.3 ) (486.0 ) Net assumed losses and loss expenses incurred $ 38.2 $ 52.0 $ 164.5 $ 167.1

Income Taxes (Tables)

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Reconciliation Between Actual Federal Income Tax Benefit and Amount Computed at Indicated Statutory Rate	The following table sets forth the reconciliation between actual federal income tax expense and the amount computed at the indicated statutory rate for the three and nine months ended September 30, 2019 and 2018 : ($ millions) Three months ended September 30 Nine months ended September 30 2019 2018 2019 2018 Amount at statutory rate $ 2.7 21.0 % $ 8.6 21.0 % $ 14.0 21.0 % $ 9.5 21.0 % Tax-exempt interest and dividends received deduction (0.7 ) (5.3 ) (0.5 ) (1.3 ) (2.1 ) (3.1 ) (1.7 ) (3.8 ) Other, net (0.8 ) (6.3 ) (0.5 ) (1.1 ) 0.1 — 0.3 0.6 Federal income tax expense 1.2 9.4 % 7.6 18.6 % 12.0 17.9 % $ 8.1 17.8 %

Pension and Postretirement Be_2

Pension and Postretirement Benefit Plans (Tables)	9 Months Ended
	Sep. 30, 2019
Retirement Benefits [Abstract]
Company's Share of Net Periodic Cost Components	for the three and nine months ended September 30, 2019 and 2018 : ($ millions) Pension Postretirement Pension Postretirement Three months ended September 30 Nine months ended September 30 2019 2018 2019 2018 2019 2018 2019 2018 Service cost $ 0.8 $ 1.2 $ — $ — $ 2.8 $ 3.8 $ — $ — Interest cost 2.9 2.7 0.2 0.2 8.6 8.0 0.5 0.5 Expected return on plan assets (4.2 ) (4.5 ) — — (12.5 ) (13.5 ) — — Amortization of: Negative prior service cost — — (1.4 ) (1.4 ) — — (4.1 ) (4.1 ) Net actuarial loss 1.5 2.1 0.1 0.1 4.5 6.2 0.2 0.2 Net periodic cost (benefit) $ 1.0 $ 1.5 $ (1.1 ) $ (1.1 ) $ 3.4 $ 4.5 $ (3.4 ) $ (3.4 )

Other Comprehensive Income an_2

Other Comprehensive Income and Accumulated Other Comprehensive Income (Tables)	9 Months Ended
	Sep. 30, 2019
Equity [Abstract]
Changes in Accumulated Other Comprehensive Income by Component, Net of Tax	The following tables set forth the changes in the Company’s accumulated other comprehensive (loss) income ("AOC(L)I"), net of tax, for the three and nine months ended September 30, 2019 and 2018 : ($ millions) Unrealized Gains and Losses on Available-for-Sale Securities Benefit Plan Items Total Beginning balance at July 1, 2019 $ 33.2 $ (74.9 ) $ (41.7 ) Other comprehensive income before reclassifications 17.8 — 17.8 Amounts reclassified from AOCI (a) (0.9 ) 0.6 (0.3 ) Net current period other comprehensive income 16.9 0.6 17.5 Ending balance at September 30, 2019 $ 50.1 $ (74.3 ) $ (24.2 ) Beginning balance at July 1, 2018 $ (20.3 ) $ (75.5 ) $ (95.8 ) Other comprehensive loss before reclassifications (11.6 ) — (11.6 ) Amounts reclassified from AOCI (a) — 1.3 1.3 Net current period other comprehensive (loss) income (11.6 ) 1.3 (10.3 ) Ending balance at September 30, 2018 $ (31.9 ) $ (74.2 ) $ (106.1 ) (a) See separate table below for details about these reclassifications ($ millions) Unrealized Gains and Losses on Available-for-Sale Securities Benefit Plan Items Total Beginning balance at January 1, 2019 $ (20.2 ) $ (76.2 ) $ (96.4 ) Other comprehensive income before reclassifications 72.5 — 72.5 Amounts reclassified from AOCI (a) (2.2 ) 1.9 (0.3 ) Net current period other comprehensive income 70.3 1.9 72.2 Ending balance at September 30, 2019 $ 50.1 $ (74.3 ) $ (24.2 ) Beginning balance at January 1, 2018 $ 66.0 $ (62.2 ) $ 3.8 Cumulative effect of change in accounting for equity securities and other invested assets and reclassification of stranded tax effects as of January 1, 2018 (47.9 ) (16.0 ) (63.9 ) Other comprehensive loss before reclassifications (48.7 ) — (48.7 ) Amounts reclassified from AOCI (a) (1.3 ) 4.0 2.7 Net current period other comprehensive (loss) income (50.0 ) 4.0 (46.0 ) Ending balance at September 30, 2018 $ (31.9 ) $ (74.2 ) $ (106.1 ) (a) See separate table below for details about these reclassifications
Schedule of Reclassifications Out of Accumulated Other Comprehensive Income by Component	The following tables set forth the reclassifications out of accumulated other comprehensive income, by component, to the Company’s condensed consolidated statement of income for the three and nine months ended September 30, 2019 and 2018 : ($ millions) Details about Accumulated Other Three months ended September 30 Affected line item in the Condensed Comprehensive Income Components Consolidated Statements of Income 2019 2018 Unrealized gains on available-for-sale fixed maturity investments $ 1.2 $ — Realized gains on sale of securities 1.2 — Total before tax (0.3 ) — Tax expense 0.9 — Net of tax Amortization of benefit plan items Negative prior service cost 1.6 1.6 (b) Net actuarial loss (2.4 ) (3.3 ) (b) (0.8 ) (1.7 ) Total before tax 0.2 0.4 Tax benefit (0.6 ) (1.3 ) Net of tax Total reclassifications for the period $ 0.3 $ (1.3 ) (b) These accumulated other comprehensive income components are included in the computation of net periodic pension cost (see pension and postretirement benefit plans footnote for additional details). ($ millions) Details about Accumulated Other Nine months ended September 30 Affected line item in the Condensed Comprehensive Income Components Consolidated Statements of Income 2019 2018 Unrealized gains on available-for-sale fixed maturity investments $ 2.8 $ 1.7 Realized gain on sale of securities 2.8 1.7 Total before tax (0.6 ) (0.4 ) Tax expense 2.2 1.3 Net of tax Amortization of benefit plan items Negative prior service cost 4.8 4.8 (b) Net actuarial loss (7.2 ) (9.9 ) (b) (2.4 ) (5.1 ) Total before tax 0.5 1.1 Tax benefit (1.9 ) (4.0 ) Net of tax Total reclassifications for the period $ 0.3 $ (2.7 ) (b) These accumulated other comprehensive income components are included in the computation of net periodic pension cost (see pension and postretirement benefit plans footnote for additional details).

Earnings per Common Share (Tabl

Earnings per Common Share (Tables)	9 Months Ended
	Sep. 30, 2019
Earnings Per Share [Abstract]
Compilation of Basic and Diluted Earnings Per Common Share	The following table sets forth the compilation of basic and diluted (loss) earnings per common share for the three and nine months ended September 30, 2019 and 2018 : ($ and shares in millions, except per share amounts) Three months ended September 30 Nine months ended September 30 2019 2018 2019 2018 Numerator: Net income for basic earnings per common share $ 11.5 $ 33.4 $ 54.7 $ 37.3 Denominator: Weighted average shares for basic (loss) earnings per common share 43.5 43.0 43.4 42.8 Effect of dilutive share-based awards 0.5 0.6 0.6 0.5 Adjusted weighted average shares for diluted net (loss) earnings per common share 44.0 43.6 44.0 43.3 Basic net earnings per common share $ 0.26 $ 0.78 $ 1.26 $ 0.87 Diluted net earnings per common share $ 0.25 $ 0.76 $ 1.25 $ 0.86
Options to Purchase Shares of Common Stock	The following table sets forth common stock options, stock awards and restricted share units ("RSU award") of the Company that were not included in the computation of diluted earnings per common share because the exercise price of the options, or awards, was greater than the average market price or their inclusion would have been antidilutive for the three and nine months ended September 30, 2019 and 2018 : (shares in millions) Three months ended September 30 Nine months ended September 30 2019 2018 2019 2018 Total number of antidilutive options and awards — — — 0.1

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2019
Segment Reporting [Abstract]
Financial Information Regarding Company's Reportable Segments	The following table sets forth financial information regarding the Company’s reportable segments and specialty run-off for the three and nine months ended September 30, 2019 and 2018 : ($ millions) Three months ended September 30 Nine months ended September 30 2019 2018 2019 2018 Revenue from external sources: Insurance operations Personal insurance $ 192.7 $ 173.0 $ 562.5 $ 494.2 Commercial insurance 127.0 115.2 361.4 345.7 Specialty run-off (0.1 ) 18.6 6.1 89.3 Total insurance operations 319.6 306.8 930.0 929.2 Investment operations Net investment income 19.3 20.8 60.4 62.2 Net investment (loss) gain (5.0 ) 17.8 50.2 18.2 Total investment operations 14.3 38.6 110.6 80.4 All other 0.6 0.6 1.6 1.8 Total revenue from external sources 334.5 346.0 1,042.2 1,011.4 Intersegment revenue 1.7 1.6 4.9 4.8 Total revenue 336.2 347.6 1,047.1 1,016.2 Reconciling items: Eliminate intersegment revenue (1.7 ) (1.6 ) (4.9 ) (4.8 ) Total consolidated revenues $ 334.5 $ 346.0 $ 1,042.2 $ 1,011.4 Segment (loss) income before federal income tax: Insurance operations SAP underwriting (loss) gain Personal insurance $ (6.3 ) $ 6.9 $ (32.0 ) $ (4.6 ) Commercial insurance 1.2 (5.2 ) (17.1 ) (22.3 ) Specialty run-off (0.6 ) 1.9 (1.3 ) 4.5 Total insurance operations (5.7 ) 3.6 (50.4 ) (22.4 ) Investment operations Net investment income 19.3 20.8 60.4 62.2 Net investment (loss) gain (5.0 ) 17.8 50.2 18.2 Total investment operations 14.3 38.6 110.6 80.4 All other — 0.1 0.2 0.3 Total segment income before reconciling items 8.6 42.3 60.4 58.3 Reconciling items: GAAP expense adjustments 7.2 0.8 17.3 (2.6 ) Interest expense on corporate debt (1.2 ) (1.2 ) (3.7 ) (4.5 ) Corporate expenses (1.9 ) (0.9 ) (7.3 ) (5.8 ) Total reconciling items 4.1 (1.3 ) 6.3 (12.9 ) Total consolidated income before federal income tax $ 12.7 $ 41.0 $ 66.7 $ 45.4

Investments - Cost or Amortized

Investments - Cost or Amortized Cost and Fair Value of Available-for-Sale Securities (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Cost or amortized cost	$ 2,129	$ 2,188.2
Gross unrealized holding gains	65.7	14.4
Gross unrealized holding losses	(5.4)	(43.1)
Fair value	2,189.3	2,159.5
U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member]
Debt Securities, Available-for-sale [Line Items]
Cost or amortized cost	516.4	438.4
Gross unrealized holding gains	14.8	3.2
Gross unrealized holding losses	(1.2)	(9.2)
Fair value	530	432.4
Obligations of States and Political Subdivisions [Member]
Debt Securities, Available-for-sale [Line Items]
Cost or amortized cost	415.3	408.2
Gross unrealized holding gains	21.8	7.3
Gross unrealized holding losses	0	(0.9)
Fair value	437.1	414.6
Corporate Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost or amortized cost	492.3	551.7
Gross unrealized holding gains	10.9	0.6
Gross unrealized holding losses	(1.1)	(11.7)
Fair value	502.1	540.6
U.S. Government Agencies Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost or amortized cost	705	789.9
Gross unrealized holding gains	18.2	3.3
Gross unrealized holding losses	(3.1)	(21.3)
Fair value	$ 720.1	$ 771.9

Investments - Available for Sal

Investments - Available for Sale Securities Continuous Unrealized Loss Position Fair Value and Aggregate Losses (Detail) $ in Millions	Sep. 30, 2019USD ($)position	Dec. 31, 2018USD ($)position
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 112.3	$ 560.2
Less than 12 months, Unrealized losses	$ (0.7)	$ (8.1)
Less than 12 months, Number of positions | position	18	63
12 months or more, Fair value	$ 406.6	$ 874.2
12 months or more, Unrealized losses	$ (4.7)	$ (35)
12 months or more, Number of positions | position	61	143
Total, Fair value	$ 518.9	$ 1,434.4
Total, Unrealized losses	$ (5.4)	$ (43.1)
Total, Number of positions | position	79	206
U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 41.1	$ 83.1
Less than 12 months, Unrealized losses	$ (0.1)	$ (1.8)
Less than 12 months, Number of positions | position	9	7
12 months or more, Fair value	$ 184.5	$ 259.6
12 months or more, Unrealized losses	$ (1.1)	$ (7.4)
12 months or more, Number of positions | position	16	35
Total, Fair value	$ 225.6	$ 342.7
Total, Unrealized losses	$ (1.2)	$ (9.2)
Total, Number of positions | position	25	42
Obligations of States and Political Subdivisions [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 0	$ 63.6
Less than 12 months, Unrealized losses	$ 0	$ (0.5)
Less than 12 months, Number of positions | position	0	7
12 months or more, Fair value	$ 4.1	$ 39.6
12 months or more, Unrealized losses	$ 0	$ (0.4)
12 months or more, Number of positions | position	1	8
Total, Fair value	$ 4.1	$ 103.2
Total, Unrealized losses	$ 0	$ (0.9)
Total, Number of positions | position	1	15
Corporate Securities [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 20.3	$ 244
Less than 12 months, Unrealized losses	$ (0.3)	$ (3)
Less than 12 months, Number of positions | position	2	31
12 months or more, Fair value	$ 56.9	$ 189.5
12 months or more, Unrealized losses	$ (0.8)	$ (8.7)
12 months or more, Number of positions | position	9	30
Total, Fair value	$ 77.2	$ 433.5
Total, Unrealized losses	$ (1.1)	$ (11.7)
Total, Number of positions | position	11	61
U.S. Government Agencies Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 50.9	$ 169.5
Less than 12 months, Unrealized losses	$ (0.3)	$ (2.8)
Less than 12 months, Number of positions | position	7	18
12 months or more, Fair value	$ 161.1	$ 385.5
12 months or more, Unrealized losses	$ (2.8)	$ (18.5)
12 months or more, Number of positions | position	35	70
Total, Fair value	$ 212	$ 555
Total, Unrealized losses	$ (3.1)	$ (21.3)
Total, Number of positions | position	42	88

Investments - Amortized Cost an

Investments - Amortized Cost and Fair Value of Available-for-Sale Fixed Maturities by Contractual Maturity (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Amortized cost
Due in 1 year or less, Amortized cost	$ 55.7
Due after 1 year through 5 years, Amortized cost	562.7
Due after 5 years through 10 years, Amortized cost	239.9
Due after 10 years, Amortized cost	565.7
U.S. government agencies mortgage-backed securities, Amortized cost	705
Total, Amortized cost	2,129	$ 2,188.2
Fair value
Due in 1 year or less, Fair value	56.6
Due after 1 year through 5 years, Fair value	569.4
Due after 5 years through 10 years, Fair value	249.7
Due after 10 years, Fair value	593.5
U.S. government agencies mortgage-backed securities, Fair value	720.1
Total, Fair value	$ 2,189.3	$ 2,159.5

Investments - Components of Net

Investments - Components of Net Investment Income (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Net Investment Income [Line Items]
Investment income	$ 19.4	$ 21.1	$ 60.8	$ 63.2
Investment expenses	0.1	0.3	0.4	1
Net investment income	19.3	20.8	60.4	62.2
Equity Securities [Member]
Net Investment Income [Line Items]
Investment income	3	3	8.9	8.6
Cash and Cash Equivalents, and Other [Member]
Net Investment Income [Line Items]
Investment income	1.1	1.7	4.2	5.2
Fixed Maturities [Member]
Net Investment Income [Line Items]
Investment income	$ 15.3	$ 16.4	$ 47.7	$ 49.4

Investments - Realized and Unre

Investments - Realized and Unrealized Holding Gains (Losses) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Debt Securities, Realized Gain (Loss):
Debt Securities, Available-for-sale, Realized Gain	$ 1.2	$ 0	$ 2.8	$ 1.7
Debt Securities, Available-for-sale, Net Realized Gain (Loss)	1.2	0	2.8	1.7
Equity Securities, FV-NI, Gain (Loss)
Other net realized loss	0	0	1.3	0
Gain (Loss) on Investments	(5)	17.8	50.2	18.2
Change in unrealized holding gains (losses), net of tax:
Change in net unrealized holding (losses) gains, net of tax	21.4	(14.7)	89	(63.3)
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax	(4.5)	3.1	(18.7)	13.3
Total net unrealized holding gain (loss) on available-for-sale investments	16.9	(11.6)	70.3	(50)
Equity Securities [Member]
Equity Securities, FV-NI, Gain (Loss)
Equity Securities, FV-NI, Realized Gain (Loss)	(1.8)	1	(2.5)	5.4
Equity Securities, FV-NI, Unrealized Gain (Loss)	(4.1)	16.4	46.4	12.8
Equity Securities, FV-NI, Net Gain (Loss)	(5.9)	17.4	43.9	18.2
Other Invested Assets [Member]
Equity Securities, FV-NI, Gain (Loss)
Equity Securities, FV-NI, Unrealized Gain (Loss)	(0.3)	0.4	4.8	(1.7)
Equity Securities, FV-NI, Net Gain (Loss)	$ (0.3)	$ 0.4	$ 4.8	$ (1.7)

Investments - Additional Inform

Investments - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Financial Instruments, Owned and Pledged as Collateral, at Fair Value	$ 23.2
Fixed maturities fair value of deposit with insurance regulators	9.3		$ 8.9
Proceeds on sale of available-for-sale securities	284.1	$ 159.9
Federal Home Loan Bank of Cincinnati [Member]
Debt Securities, Available-for-sale [Line Items]
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged	$ 106.5

Fair Value of Financial Instr_3

Fair Value of Financial Instruments - Company's Available-for-Sale Investments within Fair Value Hierarchy (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	$ 2,189.3	$ 2,159.5
Investments, Fair Value Disclosure	2,575.5	2,484.8
U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	530	432.4
Investments, Fair Value Disclosure	530	432.4
Obligations of States and Political Subdivisions [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	437.1	414.6
Investments, Fair Value Disclosure	437.1	414.6
Corporate Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	502.1	540.6
Investments, Fair Value Disclosure	502.1	540.6
U.S. Government Agencies Mortgage-Backed Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	720.1	771.9
Investments, Fair Value Disclosure	720.1	771.9
Fixed Maturities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments, Fair Value Disclosure	2,189.3	2,159.5
Large-Cap Equity Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments, Fair Value Disclosure	99.1	77.2
Mutual and exchange traded funds [Domain] [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments, Fair Value Disclosure	274.2	237.8
Equity Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments, Fair Value Disclosure	373.3	315
Other Invested Assets [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments, Fair Value Disclosure	12.9	10.3
Level 1 [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	386.2	325.3
Level 1 [Member] | U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	0	0
Level 1 [Member] | Obligations of States and Political Subdivisions [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	0	0
Level 1 [Member] | Corporate Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	0	0
Level 1 [Member] | U.S. Government Agencies Mortgage-Backed Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	0	0
Level 1 [Member] | Fixed Maturities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	0	0
Level 1 [Member] | Large-Cap Equity Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	99.1	77.2
Level 1 [Member] | Mutual and exchange traded funds [Domain] [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	274.2	237.8
Level 1 [Member] | Equity Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	373.3	315
Level 1 [Member] | Other Invested Assets [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	12.9	10.3
Level 2 [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	2,189.3	2,159.5
Level 2 [Member] | U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	530	432.4
Level 2 [Member] | Obligations of States and Political Subdivisions [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	437.1	414.6
Level 2 [Member] | Corporate Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	502.1	540.6
Level 2 [Member] | U.S. Government Agencies Mortgage-Backed Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	720.1	771.9
Level 2 [Member] | Fixed Maturities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	2,189.3	2,159.5
Level 2 [Member] | Large-Cap Equity Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	0	0
Level 2 [Member] | Mutual and exchange traded funds [Domain] [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	0	0
Level 2 [Member] | Equity Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	0	0
Level 2 [Member] | Other Invested Assets [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	$ 0	$ 0

Fair Value of Financial Instr_4

Fair Value of Financial Instruments - Company Estimates Receivable from Affiliate using Market Quotations for U.S. Treasury Securities (Detail) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Document Period End Date	Sep. 30, 2019
Affiliated Entity [Member] | Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable interest rate (percent)		7.00%
Note Receivable from Affiliate, 2009 [Member] | Affiliated Entity [Member] | Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable interest rate (percent)	0.00%	7.00%
Note Receivable from Affiliate, 2019 [Member] | Affiliated Entity [Member] | Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable interest rate (percent)	4.05%	0.00%
Reported Value Measurement [Member] | Note Receivable from Affiliate, 2009 [Member] | Affiliated Entity [Member] | Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable from affiliate	$ 0	$ 70
Reported Value Measurement [Member] | Note Receivable from Affiliate, 2019 [Member] | Affiliated Entity [Member] | Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable from affiliate	70	0
Estimate of Fair Value Measurement [Member] | Note Receivable from Affiliate, 2009 [Member] | Affiliated Entity [Member] | Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable from affiliate	0	71.1
Estimate of Fair Value Measurement [Member] | Note Receivable from Affiliate, 2019 [Member] | Affiliated Entity [Member] | Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable from affiliate	$ 76.8	$ 0

Fair Value of Financial Instr_5

Fair Value of Financial Instruments - Included in Notes Payable are the FHLB loan and Subordinated Debentures (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Document Period End Date	Sep. 30, 2019
Federal Home Loan Bank Advances [Member]
Debt Instrument [Line Items]
Interest rate (percent)	1.73%	1.73%
FHLB loan due and issued with fixed interest, Senior notes due and issued with fixed interest and Affiliate subordinated debentures due with variable interest	$ 21,500,000
Federal Home Loan Bank of Cincinnati [Member]
Debt Instrument [Line Items]
FHLB loan due and issued with fixed interest, Senior notes due and issued with fixed interest and Affiliate subordinated debentures due with variable interest	$ 85,000,000
Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Interest rate (percent)	3.96%	3.96%
Affiliate Subordinated Debentures Due 2033 [Member]
Debt Instrument [Line Items]
Interest rate (percent)	6.33%	6.94%
FHLB loan due and issued with fixed interest, Senior notes due and issued with fixed interest and Affiliate subordinated debentures due with variable interest	$ 15,500,000
Reported Value Measurement [Member]
Debt Instrument [Line Items]
Total notes payable	122,000,000	$ 122,000,000
Reported Value Measurement [Member] | Federal Home Loan Bank Advances [Member]
Debt Instrument [Line Items]
Total notes payable	21,500,000	21,500,000
Reported Value Measurement [Member] | Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Total notes payable	85,300,000	85,300,000
Reported Value Measurement [Member] | Affiliate Subordinated Debentures Due 2033 [Member]
Debt Instrument [Line Items]
Total notes payable	15,200,000	15,200,000
Estimate of Fair Value Measurement [Member]
Debt Instrument [Line Items]
Total notes payable	136,800,000	125,100,000
Estimate of Fair Value Measurement [Member] | Federal Home Loan Bank Advances [Member]
Debt Instrument [Line Items]
Total notes payable	21,500,000	20,900,000
Estimate of Fair Value Measurement [Member] | Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Total notes payable	100,100,000	89,000,000
Estimate of Fair Value Measurement [Member] | Affiliate Subordinated Debentures Due 2033 [Member]
Debt Instrument [Line Items]
Total notes payable	$ 15,200,000	$ 15,200,000

Fair Value of Financial Instr_6

Fair Value of Financial Instruments - Additional Information (Detail) $ in Millions	1 Months Ended		12 Months Ended
	May 31, 2019Agreement	May 31, 2009Agreement	Dec. 31, 2018USD ($)	Sep. 30, 2019USD ($)
Fair Value Measurements Disclosure [Line Items]
Other invested assets			$ 48.8	$ 64.6
Other invested assets, at cost			5.6	6.5
Number of Credit Agreements | Agreement	2	2
Notes receivable from affiliate			70	70
Level 3 [Member]
Fair Value Measurements Disclosure [Line Items]
Federal home loan bank stock				6
Other invested assets, at cost				$ 0.5
International funds [Member]
Fair Value Measurements Disclosure [Line Items]
Number of available for sale securities				1
Other invested assets			$ 38.5	$ 51.7
Affiliated Entity [Member]
Fair Value Measurements Disclosure [Line Items]
Notes receivable from affiliate				$ 70
Affiliated Entity [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Measurements Disclosure [Line Items]
Notes receivable interest rate (percent)			7.00%

Losses and Loss Expenses Paya_3

Losses and Loss Expenses Payable Losses and Loss Expenses Payable - Schedule of Activity in Liability for Unpaid Losses and Loss Expenses Payable (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Losses and Loss Expenses Payable [Abstract]
Liability for Claims and Claims Adjustment Expense, Property Casualty Liability	$ 1,092.7	$ 1,198.7	$ 1,092.7	$ 1,198.7	$ 1,146.8	$ 1,255.6
Reinsurance Recoverables, Including Reinsurance Premium Paid	7.2	5	7.2	5	5.5	3.1
Liability for Unpaid Claims and Claims Adjustment Expense, Net	1,085.5	1,193.7	1,085.5	1,193.7	$ 1,141.3	$ 1,252.5
Current Year Claims and Claims Adjustment Expense			692.7	678.7
Prior Year Claims and Claims Adjustment Expense			(55.1)	(57.6)
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	$ 208.4	$ 191	637.6	621.1
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year			366.4	314.1
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years			327	365.8
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid			$ 693.4	$ 679.9

Losses and Loss Expenses Paya_4

Losses and Loss Expenses Payable Losses and Loss Expenses Payable - Additional Information (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Liability for Claims and Claims Adjustment Expense [Line Items]
Document Period End Date	Sep. 30, 2019
Prior Year Claims and Claims Adjustment Expense	$ (55.1)	$ (57.6)
Business Insurance Segments [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense		(56.4)
Specialty Insurance [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense		(4.1)
Homeowners [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense		(7.2)
Middle Market Commercial [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	(7.2)
Personal Auto [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	(11)	(18.5)
Commercial Auto [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense		(5.7)
Workers' compensation [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	(13.4)	(8.4)
E&S Casualty [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense		(3.4)
Programs [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense		(0.9)
Small commercial [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	(11.8)	$ (6.5)
Total Insurance Segments [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	$ (54.1)

Reinsurance - Summary of Extern

Reinsurance - Summary of External Reinsurance Transactions, as well as reinsurance transactions with State Auto Mutual Under the Pooling Arrangement (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Premiums earned:
Assumed from external insurers and reinsurers	$ 21	$ 17.3	$ 59.3	$ 41.9
Assumed under Pooling Arrangement	319.6	306.8	930	929.2
Ceded to external insurers and reinsurers	(6.6)	(5.9)	(18.8)	(16.7)
Ceded under Pooling Arrangement	(263.9)	(234.9)	(761.5)	(678.1)
Net assumed premiums earned	70.1	83.3	209	276.3
Losses and loss expenses incurred:
Assumed from external insurers and reinsurers	14.6	10.9	45.6	34.2
Assumed under Pooling Arrangement	209.3	191.4	639.4	622.3
Ceded to external insurers and reinsurers	(0.6)	(1.9)	(6.2)	(3.4)
Ceded under Pooling Arrangement	(185.1)	(148.4)	(514.3)	(486)
Net assumed losses and loss expenses incurred	$ 38.2	$ 52	$ 164.5	$ 167.1

Notes Payable and Open Line of

Notes Payable and Open Line of Credit Notes Payable and Open Line of Credit (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Debt Disclosure [Abstract]
Debt Prepayment Cost	$ 0	$ 0.4

Income Taxes - Reconciliation B

Income Taxes - Reconciliation Between Actual Federal Income Tax Expense (Benefit) and Amount Computed at Indicated Statutory Rate (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Amount at statutory rate	$ 2.7	$ 8.6	$ 14	$ 9.5
Tax-exempt interest and dividends received deduction	(0.7)	(0.5)	(2.1)	(1.7)
Other, net	(0.8)	(0.5)	0.1	0.3
Federal income tax expense and effective rate	1.2	7.6	12	8.1
Income Tax Expense (Benefit)	$ 1.2	$ 7.6	$ 12	$ 8.1
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Amount at statutory rate (percent)	21.00%	21.00%	21.00%	21.00%
Tax-exempt interest and dividends received deduction (percent)	(5.30%)	(1.30%)	(3.10%)	(3.80%)
Other, net (percent)	(6.30%)	(1.10%)	0.00%	0.60%
Effective Income Tax Rate Reconciliation, Deduction, Percent	9.40%	18.60%	17.90%	17.80%

Pension and Postretirement Be_3

Pension and Postretirement Benefit Plans - Company's Share of Net Periodic Cost Components (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pension [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 0.8	$ 1.2	$ 2.8	$ 3.8
Interest cost	2.9	2.7	8.6	8
Expected return on plan assets	(4.2)	(4.5)	(12.5)	(13.5)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	0	0	0	0
Amortization of:
Defined Benefit Plan, Amortization of Gain (Loss)	1.5	2.1	4.5	6.2
Net periodic cost (benefit)	1	1.5	3.4	4.5
Postretirement [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	0	0	0	0
Interest cost	0.2	0.2	0.5	0.5
Expected return on plan assets	0	0	0	0
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	(1.4)	(1.4)	(4.1)	(4.1)
Amortization of:
Defined Benefit Plan, Amortization of Gain (Loss)	0.1	0.1	0.2	0.2
Net periodic cost (benefit)	$ (1.1)	$ (1.1)	$ (3.4)	$ (3.4)

Pension and Postretirement Be_4

Pension and Postretirement Benefit Plans - Additional Information (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2019USD ($)
Retirement Benefits [Abstract]
Contributions by employer	$ 10

Other Comprehensive Income an_3

Other Comprehensive Income and Accumulated Other Comprehensive Income - Schedule of Changes in Accumulated Other Comprehensive Income by Component, Net of Tax (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Beginning balance	$ (41.7)	$ (95.8)	$ (96.4)	$ 3.8
Cumulative Effect of change in accounting for equity securities and other invested assets and reclassification of stranded tax effects as of January 1, 2018					$ (63.9)
Other comprehensive income before reclassifications	17.8	(11.6)	72.5	(48.7)
Amounts reclassified from AOCI	(0.3)	1.3	(0.3)	2.7
Other comprehensive income (loss)	17.5	(10.3)	72.2	(46)
Ending balance	(24.2)	(106.1)	(24.2)	(106.1)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Amounts reclassified from AOCI	(0.3)	1.3	(0.3)	2.7
Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Beginning balance	33.2	(20.3)	(20.2)	66
Cumulative Effect of change in accounting for equity securities and other invested assets and reclassification of stranded tax effects as of January 1, 2018					(47.9)
Other comprehensive income before reclassifications	17.8	(11.6)	72.5	(48.7)
Amounts reclassified from AOCI	(0.9)	0	(2.2)	(1.3)
Other comprehensive income (loss)	16.9	(11.6)	70.3	(50)
Ending balance	50.1	(31.9)	50.1	(31.9)
Benefit Plan Items [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Beginning balance	(74.9)	(75.5)	(76.2)	(62.2)
Cumulative Effect of change in accounting for equity securities and other invested assets and reclassification of stranded tax effects as of January 1, 2018					$ (16)
Other comprehensive income before reclassifications	0	0	0	0
Amounts reclassified from AOCI	0.6	1.3	1.9	4
Other comprehensive income (loss)	0.6	1.3	1.9	4
Ending balance	$ (74.3)	$ (74.2)	$ (74.3)	$ (74.2)

Other Comprehensive Income an_4

Other Comprehensive Income and Accumulated Other Comprehensive Income - Schedule of Reclassifications Out of Accumulated Other Comprehensive Income by Component (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gain/(loss) on sale of securities	$ (5)	$ 17.8	$ 50.2	$ 18.2
Tax (expense) benefit	(1.2)	(7.6)	(12)	(8.1)
Total reclassifications for the period	0.3	(1.3)	0.3	(2.7)
Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period	0.9	0	2.2	1.3
Benefit Plan Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period	(0.6)	(1.3)	(1.9)	(4)
Reclassification Out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period	0.3	(1.3)	0.3	(2.7)
Reclassification Out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gain/(loss) on sale of securities	1.2	0	2.8	1.7
Total before tax	1.2	0	2.8	1.7
Tax (expense) benefit	(0.3)	0	(0.6)	(0.4)
Net of tax	0.9	0	2.2	1.3
Reclassification Out of Accumulated Other Comprehensive Income [Member] | Benefit Plan Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Accumulated other comprehensive income components/Negative prior-service costs	1.6	1.6	4.8	4.8
Accumulated other comprehensive income components/Net actuarial loss	(2.4)	(3.3)	(7.2)	(9.9)
Total before tax	(0.8)	(1.7)	(2.4)	(5.1)
Tax (expense) benefit	0.2	0.4	0.5	1.1
Net of tax	$ (0.6)	$ (1.3)	$ (1.9)	$ (4)

Earnings Per Common Share - Com

Earnings Per Common Share - Compilation of Basic and Diluted Earnings (Loss) Per Common Share (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator:
Net income	$ 11.5	$ 33.4	$ 54.7	$ 37.3
Denominator:
Weighted average shares for basic net earnings per common share (shares)	43,500,000	43	43,400,000	42.8
Effect of dilutive share-based awards (shares)	500,000	0.6	600,000	0.5
Adjusted weighted average shares for diluted net earnings per common share (shares)	44,000,000	43.6	44,000,000	43.3
Basic net (loss) earnings per common share (usd per share)	$ 0.26	$ 0.78	$ 1.26	$ 0.87
Diluted net (loss) earnings per common share (usd per share)	$ 0.25	$ 0.76	$ 1.25	$ 0.86

Earnings Per Common Share - Opt

Earnings Per Common Share - Options to Purchase Shares of Common Stock (Detail) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Number of antidilutive options and awards	0	0	0	0.1

Segment Information - Financial

Segment Information - Financial Information Regarding Company's Reportable Segments (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenues from external sources:
Revenue	$ 334.5	$ 346	$ 1,042.2	$ 1,011.4
Other Income	0.6	0.6	1.6	1.8
Net Investment Income	19.3	20.8	60.4	62.2
Realized Investment Gains (Losses)	(5)	17.8	50.2	18.2
Segment income before federal income tax:
Interest expense on corporate debt	(1.2)	(1.2)	(3.7)	(4.5)
Income before federal income taxes	12.7	41	66.7	45.4
Operating Segments [Member]
Revenues from external sources:
Revenue	334.5	346	1,042.2	1,011.4
Segment income before federal income tax:
Income before federal income taxes	8.6	42.3	60.4	58.3
Operating Segments [Member] | Personal Insurance Segments [Member]
Revenues from external sources:
Revenue	192.7	173	562.5	494.2
Operating Segments [Member] | Business Insurance Segments [Member]
Revenues from external sources:
Revenue	127	115.2	361.4	345.7
Operating Segments [Member] | Specialty Insurance Segment [Member]
Revenues from external sources:
Revenue	(0.1)	18.6	6.1	89.3
Operating Segments [Member] | Total Insurance Segments [Member]
Revenues from external sources:
Revenue	319.6	306.8	930	929.2
Segment income before federal income tax:
Income before federal income taxes	(5.7)	3.6	(50.4)	(22.4)
Operating Segments [Member] | Net Investment Income [Member]
Revenues from external sources:
Net Investment Income	19.3	20.8	60.4	62.2
Operating Segments [Member] | Total Investment Operations [Member]
Revenues from external sources:
Revenue	14.3	38.6	110.6	80.4
Segment income before federal income tax:
Income before federal income taxes	14.3	38.6	110.6	80.4
Operating Segments [Member] | Total Investment Operations [Member] | Net Realized Capital Gains [Member]
Segment income before federal income tax:
Income before federal income taxes	(5)	17.8	50.2	18.2
Operating Segments [Member] | All Other Segments [Member]
Revenues from external sources:
Revenue		0.6		1.8
Segment income before federal income tax:
Income before federal income taxes	0	0.1	0.2	0.3
Operating Segments [Member] | Personal Insurance [Member]
Segment income before federal income tax:
Income before federal income taxes	(6.3)	6.9	(32)	(4.6)
Operating Segments [Member] | Business Insurance [Member]
Segment income before federal income tax:
Income before federal income taxes	1.2	(5.2)	(17.1)	(22.3)
Operating Segments [Member] | Specialty Insurance [Member]
Segment income before federal income tax:
Income before federal income taxes	(0.6)	1.9	(1.3)	4.5
Eliminate Intersegment Revenues [Member]
Revenues from external sources:
Revenue	1.7	1.6	4.9	4.8
Segment Reconciling Items [Member]
Revenues from external sources:
Revenue	(1.7)	(1.6)	(4.9)	(4.8)
Segment income before federal income tax:
Corporate Expenses	(1.9)	(0.9)	(7.3)	(5.8)
Income before federal income taxes	4.1	(1.3)	6.3	(12.9)
Segment Reconciling Items [Member] | Segment Reconciling Items [Member]
Segment income before federal income tax:
Gaap Expense Adjustments	7.2	0.8	17.3	(2.6)
Interest expense on corporate debt	1.2	1.2	3.7	4.5
Corporate And Reconciling Items [Member]
Revenues from external sources:
Revenue	$ 336.2	$ 347.6	$ 1,047.1	$ 1,016.2

Segment Information - Additiona

Segment Information - Additional Information (Detail) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2019USD ($)Segment	Sep. 30, 2018USD ($)	Dec. 31, 2018USD ($)
Segment Reporting Information [Line Items]
Acquisition And Operating Expenses	$ 109.7	$ 110.9	$ 325.2	$ 333
Number of reportable segments (segments) | Segment			3
Investable assets	$ 2,742		$ 2,742		$ 2,658.7