Selective Insurance (SIGI) 10-Q 29 Oct 20 2020 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2020	Oct. 16, 2020
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2020
Document Transition Report	false
Entity File Number	001-33067
Entity Registrant Name	SELECTIVE INSURANCE GROUP, INC
Entity Incorporation, State or Country Code	NJ
Entity Tax Identification Number	22-2168890
Entity Address, Address Line One	40 Wantage Avenue
Entity Address, City or Town	Branchville
Entity Address, State or Province	NJ
Entity Address, Postal Zip Code	07890
City Area Code	973
Local Phone Number	948-3000
Title of 12(b) Security	Common Stock, par value $2 per share
Trading Symbol	SIGI
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		59,834,702
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Entity Central Index Key	0000230557
Current Fiscal Year End Date	--12-31

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
ASSETS
Fixed income securities, held-to-maturity, carrying value	$ 19,111	$ 20,800
Less: allowance for credit losses	(24)	0
Fixed income securities, held-to-maturity, net of allowance for credit losses	19,087	20,800
Fixed income securities, available-for-sale, fair value	6,437,537	6,095,620
Commercial mortgage loans, carrying value	29,691	0
Less: allowance for credit losses	(217)	0
Commercial mortgage loans, net of allowance for credit losses	29,474	0
Equity Securities, fair value	151,824	72,937
Short-term investments (at cost which approximates fair value)	380,890	282,490
Other investments	258,648	216,807
Total investments (Note 4 and 6)	7,277,460	6,688,654
Cash	785	300
Restricted cash	15,110	7,675
Interest and dividends due or accrued	46,392	44,846
Premiums receivable	872,082	830,301
Less: allowance for credit losses (Note 7)	(21,000)	(6,400)
Premiums receivable, net of allowance for credit losses	851,082	823,901
Reinsurance recoverable	613,287	577,635
Allowance for credit losses	(1,831)	(4,400)
Reinsurance recoverable, net of allowance for credit losses	611,456	573,235
Prepaid reinsurance premiums	179,415	166,705
Current federal income tax	6,563	0
Deferred federal income tax	0	6,776
Property and equipment, at cost, net of accumulated depreciation and amortization	78,443	77,409
Deferred policy acquisition costs	292,709	271,186
Goodwill	7,849	7,849
Other assets	147,662	128,614
Total assets	9,514,926	8,797,150
Liabilities And Stockholders' Equity
Reserve for loss and loss expense (Note 9)	4,293,276	4,067,163
Unearned premiums	1,650,549	1,523,167
Short-term debt (Note 5)	167,000	0
Long-term Debt (Note 5)	550,566	550,597
Current federal income tax	0	2,987
Deferred federal income tax	20,400	0
Accrued salaries and benefits	93,076	126,753
Other liabilities	346,446	331,547
Total liabilities	7,121,313	6,602,214
Stockholders' Equity:
Preferred stock of $0 par value per share	0	0
Common stock of $2 par value per share	207,923	206,968
Additional paid-in capital	438,874	418,521
Retained earnings	2,159,597	2,080,529
Accumulated other comprehensive income (Note 12)	187,090	81,750
Treasury Stock, cost	(599,871)	(592,832)
Total stockholders' equity	2,393,613	2,194,936
Commitments and contingencies
Total liabilities and stockholders' equity	$ 9,514,926	$ 8,797,150

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues:
Net premiums earned	$ 694,541	$ 653,620	$ 1,976,915	$ 1,928,812
Net investment income earned	68,185	55,826	158,596	164,949
Net realized and unrealized gains (losses):
Net realized investment gains on disposals	573	20,425	7,288	26,752
Unrealized gains (losses) on equity securities	4,338	(20,317)	(7,098)	(8,091)
Other-than-temporary impairment benefit (expense)	2,810	(2,291)	(24,486)	(3,366)
Total net realized and unrealized gains (losses)	7,721	(2,183)	(24,296)	15,295
Other income	6,119	3,162	12,627	8,535
Total revenues	776,566	710,425	2,123,842	2,117,591
Expenses:
Loss and loss expense incurred	447,802	398,675	1,252,075	1,166,238
Amortization of deferred policy acquisition costs	142,291	136,572	415,723	399,647
Other insurance expenses	89,530	90,234	269,477	261,975
Interest expense	7,781	7,397	23,310	26,289
Corporate expenses	3,905	6,369	19,310	28,345
Total expenses	691,309	639,247	1,979,895	1,882,494
Income before federal income tax	85,257	71,178	143,947	235,097
Federal income tax expense:
Current	17,412	13,805	25,948	44,344
Deferred	(2,030)	1,223	(1,295)	989
Total federal income tax expense	15,382	15,028	24,653	45,333
Net income	$ 69,875	$ 56,150	$ 119,294	$ 189,764
Earnings per share:
Basic net income	$ 1.17	$ 0.94	$ 1.99	$ 3.20
Diluted net income	$ 1.16	$ 0.93	$ 1.98	$ 3.16

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Net income	$ 69,875	$ 56,150	$ 119,294	$ 189,764
Unrealized holding gains arising during period	29,889	27,168	104,771	174,483
Non-Credit Portion of OTTI recognized in OCI	7,299	0	(14,751)	0
Amounts reclassified into net income: Held-to-maturity securities	0	(2)	(5)	(26)
Amounts reclassified into net income: Net realized (gains) losses on disposals and intent-to-sell OTTI on AFS securities	(406)	2,229	7,210	351
Amounts reclassified into net income: Credit loss (benefit) expense recognized in OTTI	(2,254)	0	6,328	0
Total Unrealized Gains Losses on Investment Securities, Net	34,528	29,395	103,553	174,808
Amount reclassified into net income: Net actuarial loss	596	525	1,787	1,574
Total defined benefit pension and post-retirement plans, Net	596	525	1,787	1,574
Other Comprehensive Income, Net	35,124	29,920	105,340	176,382
Comprehensive Income, Net	$ 104,999	$ 86,070	$ 224,634	$ 366,146

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional paid-in capital [Member]	Retained Earnings [Member]	Retained Earnings [Member]Accounting Standards Update 2016-02 [Member]	Retained Earnings [Member]Accounting Standards Update 2016-13 [Member]	Retained Earnings [Member]Cumulative Effect, Period of Adoption, Adjustment	Accumulated other comprehensive income (loss) [Member]	Treasury stock [Member]
Beginning of year at Dec. 31, 2018		$ 205,697	$ 390,315	$ 1,858,414	$ 342	$ 0	$ 1,858,756	$ (77,956)	$ (584,668)
Dividend reinvestment plan		31	1,095
Stock purchase and compensation plans		1,115	20,937
Net income	$ 189,764			189,764
Dividends to stockholders				(36,021)
Other comprehensive income	176,382							176,382
Acquisition of treasury stock									(8,071)
End of period at Sep. 30, 2019	$ 2,137,376	206,843	412,347	2,012,499				98,426	(592,739)
Dividends declared per share to stockholders	$ 0.60
Common stock, shares outstanding, beginning of period at Dec. 31, 2018	58,948,554
Dividend reinvestment plan, shares	15,650
Stock purchase and compensation plan, shares	557,257
Acquisition of treasury stock, shares	(121,892)
Common stock, shares outstanding, end of period at Sep. 30, 2019	59,399,569
Beginning of year at Jun. 30, 2019		206,665	407,382	1,968,374	0	0	1,968,374	68,506	(591,383)
Dividend reinvestment plan		9	366
Stock purchase and compensation plans		169	4,599
Net income	$ 56,150			56,150
Dividends to stockholders				(12,025)
Other comprehensive income	29,920							29,920
Acquisition of treasury stock									(1,356)
End of period at Sep. 30, 2019	$ 2,137,376	206,843	412,347	2,012,499				98,426	(592,739)
Dividends declared per share to stockholders	$ 0.20
Common stock, shares outstanding, beginning of period at Jun. 30, 2019	59,328,108
Dividend reinvestment plan, shares	4,738
Stock purchase and compensation plan, shares	83,979
Acquisition of treasury stock, shares	(17,256)
Common stock, shares outstanding, end of period at Sep. 30, 2019	59,399,569
Beginning of year at Dec. 31, 2019	$ 2,194,936	206,968	418,521	2,080,529	0	1,435	2,081,964	81,750	(592,832)
Dividend reinvestment plan		44	1,216
Stock purchase and compensation plans		911	19,137
Net income	119,294			119,294
Dividends to stockholders				(41,661)
Other comprehensive income	105,340							105,340
Acquisition of treasury stock									(7,039)
End of period at Sep. 30, 2020	$ 2,393,613	207,923	438,874	2,159,597				187,090	(599,871)
Dividends declared per share to stockholders	$ 0.69
Common stock, shares outstanding, beginning of period at Dec. 31, 2019	59,461,153
Dividend reinvestment plan, shares	21,900
Stock purchase and compensation plan, shares	455,537
Acquisition of treasury stock, shares	(103,888)
Common stock, shares outstanding, end of period at Sep. 30, 2020	59,834,702
Beginning of year at Jun. 30, 2020		207,875	435,019	2,103,629	$ 0	$ 0	$ 2,103,629	151,966	(599,814)
Dividend reinvestment plan		14	401
Stock purchase and compensation plans		34	3,454
Net income	$ 69,875			69,875
Dividends to stockholders				(13,907)
Other comprehensive income	35,124							35,124
Acquisition of treasury stock									(57)
End of period at Sep. 30, 2020	$ 2,393,613	$ 207,923	$ 438,874	$ 2,159,597				$ 187,090	$ (599,871)
Dividends declared per share to stockholders	$ 0.23
Common stock, shares outstanding, beginning of period at Jun. 30, 2020	59,811,742
Dividend reinvestment plan, shares	7,026
Stock purchase and compensation plan, shares	16,936
Acquisition of treasury stock, shares	(1,002)
Common stock, shares outstanding, end of period at Sep. 30, 2020	59,834,702

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Operating Activities
Net income	$ 119,294	$ 189,764
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization	44,435	42,346
Stock-based compensation expense	13,935	15,857
Undistributed gains of equity method investments	(5,146)	(8,832)
Distributions in excess of current year income of equity method investments	3,136	2,267
Net realized and unrealized losses (gains)	24,296	(15,295)
Loss (gain) on disposal of fixed assets	17	(21)
Changes in assets and liabilities:
Increase in reserve for loss and loss expense, net of reinsurance recoverable	190,796	134,951
Increase in unearned premiums, net of prepaid reinsurance	114,672	122,460
(Increase) decrease in net federal income taxes	(10,775)	2,408
Increase in premiums receivable	(28,239)	(89,962)
Increase in deferred policy acquisition costs	(21,523)	(26,627)
Increase in interest and dividends due or accrued	(1,507)	(1,460)
Decrease in accrued salaries and benefits	(33,677)	(16,261)
Increase in other assets	(23,388)	(35,810)
(Decrease) increase in other liabilities	(5,443)	414
Net Cash Provided by Operating Activities	380,883	316,199
Investing Activities
Purchase of fixed income securities, available-for-sale	(1,373,226)	(1,330,827)
Purchase of commercial mortgage loans	(29,800)	0
Purchase of equity securities	(87,307)	(40,233)
Purchase of other investments	(61,051)	(41,248)
Purchase of short-term investments	(4,475,128)	(4,108,414)
Sale of fixed income securities, available-for-sale	411,263	461,825
Proceeds from commercial mortgage loans	109	0
Sale of short-term investments	4,377,024	4,106,643
Redemption and maturities of fixed income securities, held-to-maturity	1,646	10,062
Redemption and maturities of fixed income securities, available-for-sale	738,238	413,220
Sale of equity securities	1,320	125,302
Sale of other investments	3,879	18,016
Distributions from other investments	12,890	19,054
Purchase of property and equipment	(17,858)	(24,424)
Fixed asset disposals	0	35
Net Cash Used in Investing Activities	(498,001)	(390,989)
Financing Activities
Dividends to stockholders	(39,972)	(34,440)
Acquisition of treasury stock	(7,039)	(8,071)
Net proceeds from stock purchase and compensation plans	5,478	5,599
Proceeds from borrowings	487,000	355,757
Repayments of borrowings	(320,000)	(250,000)
Repayments of finance lease obligations	(429)	(811)
Net Cash Provided by Financing Activities	125,038	68,034
Cash and restricted cash, beginning of year	7,975	16,919
Cash and restricted cash, end of period	15,895	10,163
Net increase (decrease) in cash and restricted cash	$ 7,920	$ (6,756)

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Consolidated Balance Sheets (Parentheticals) [Line Items]
Fixed income securities, held-to-maturity, fair value	$ 20,213	$ 21,975
Fixed income securities, available-for-sale, allowance for credit losses	7,180	0
Fixed income securities, available-for-sale, amortized cost	6,097,973	5,879,986
Commercial mortgage loan, fair value	30,595
Equity Securities, cost	158,045	72,061
Property and equipment, accumulated depreciation and amortization	$ 240,057	$ 227,566
Preferred stock, par value per share	$ 0	$ 0
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred Stock, Shares Outstanding	0	0
Common stock, par value per share	$ 2	$ 2
Common stock, shares authorized	360,000,000	360,000,000
Common stock, shares issued	103,961,596	103,484,159
Treasury stock, shares	44,126,894	44,023,006

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity (Parentheticals) - $ / shares	Sep. 30, 2020	Dec. 31, 2019
Preferred stock, par value per share	$ 0	$ 0
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Series A Preferred Stock [Member]
Preferred stock, par value per share	$ 0	$ 0
Preferred stock, shares authorized	300,000	300,000

Basis of Presentation

Basis of Presentation	9 Months Ended
	Sep. 30, 2020
Basis of Presentation And Significant Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation and Accounting Policies (a) Basis of Presentation The words "Company,” “we,” “us,” or “our” refer to Selective Insurance Group, Inc. (the "Parent") and its subsidiaries, except as expressly indicated or the context requires otherwise. We have prepared our interim unaudited consolidated financial statements (“Financial Statements”) in conformity with U.S. generally accepted accounting principles (“GAAP”) and the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”) regarding interim financial reporting. These require us to make estimates and assumptions that affect the reported financial statement balances and the disclosure of contingent assets and liabilities. Actual results could differ from those estimates. All significant intercompany accounts and transactions between the Parent and its subsidiaries are eliminated in consolidation. Our Financial Statements reflect all adjustments that, in our opinion, are normal, recurring, and necessary for a fair presentation of our results of operations and financial condition. Our Financial Statements cover the third quarters ended September 30, 2020 (“Third Quarter 2020”) and September 30, 2019 (“Third Quarter 2019”) and the nine-month periods ended September 30, 2020 ("Nine Months 2020") and September 30, 2019 ("Nine Months 2019"). Our Financial Statements do not include all information and disclosures required by GAAP and the SEC for audited annual financial statements. Because results of operations for any interim period are not necessarily indicative of results for a full year, our Financial Statements should be read in conjunction with the consolidated financial statements contained in our Annual Report on Form 10-K for the year ended December 31, 2019 (“2019 Annual Report”) filed with the SEC. (b) Accounting Policies We have made no material changes in the accounting policies disclosed in Note 2. "Summary of Significant Accounting Policies" in Item 8. “Financial Statements and Supplementary Data.” of our 2019 Annual Report other than (i) those associated with our adoption of ASU 2016-13, Financial Instruments - Credit Losses ("CECL") in the first quarter of 2020 and (ii) our recent investment allocation to commercial mortgage loans ("CMLs"). The changes to our accounting policies are related to the following items: (i) Investments; (ii) Allowance for Uncollectible Premiums Receivable; and (iii) Allowance for Uncollectible Reinsurance Recoverable. Investments Fixed Income Securities We have updated our policy associated with our review of fixed income securities for other-than-temporary impairments ("OTTI"), and we follow a two-step process: (i) We review our fixed income securities in an unrealized loss position to determine (i) if we have the intent to sell the security, or (ii) if it is more likely than not we will be required to sell the security before its anticipated recovery. If we determine that we have the intent or likely requirement to sell the security, we write down its amortized cost to its fair value. In writing down amortized cost, any amount previously recorded as an allowance for credit losses is reversed and any incremental impairment is recorded directly to earnings as OTTI. (ii) If we do not have either the intent or likely requirement to sell the security, we evaluate expected credit losses primarily by performing a discounted cash flow (“DCF”) analysis on each of our fixed income securities to determine if an allowance for credit loss is required. We incorporate the results of the DCF analysis on individual security holdings into our calculation of the allowance for credit losses as follows: • For our held-to-maturity ("HTM") portfolio, the allowance for credit losses is the shortfall between amortized cost at the reporting date and the present value of future cash flows calculated in the DCF analysis. • For our available-for-sale ("AFS") portfolio and fixed income securities included in our short-term investment portfolio, the allowance for credit losses is calculated in the same manner as for the HTM portfolio; but the allowance amount is limited to the difference between the security’s amortized cost and fair value, or the fair value floor. This treatment is appropriate, as we have the ability to recover the amortized cost of an AFS security either through (i) collection of the contractual cash flows or (ii) sale of the security. Fair value declines on our AFS securities not recorded through OTTI are recognized in Accumulated other comprehensive income ("AOCI"), after tax. Our DCF analyses calculate the present value of future cash flows using various models specific to the major security types in our portfolio. These models use security-specific information as well as forecasted macroeconomic data to determine possible expected credit loss scenarios based on projected changes in the economy. The forecasted economic data incorporated into the models is based on the Federal Reserve Board’s annual supervisory stress test review on certain large banks and financial institutions. We also have the ability to incorporate internally-developed forecast information into the models as we deem appropriate. Model scenarios include a baseline assumption with projections for moderate economic expansion, an adverse assumption with projections for a weakening economy, and a severely adverse assumption with projections for a global recession. In developing our best estimate of the allowance for credit losses, we consider our outlook as to the probability of each of these scenarios occurring over the estimated contractual cash flows of our investment portfolio. For additional information about the various assumptions we make, including the discount rates used in our DCF analyses, see Note 2. "Summary of Significant Accounting Policies" in Item 8. “Financial Statements and Supplementary Data.” of our 2019 Annual Report. The allowance for credit losses is recorded as a contra-asset reflected in the carrying value of the investment on the Consolidated Balance Sheet, and is charged to earnings as credit loss expense, which is a component of "Other-than-temporary impairment benefit (expense)" within "Net realized and unrealized gains (losses)" on our Consolidated Statements of Income. The income statement treatment is consistent with how we accounted for credit losses prior to the adoption of CECL. Subsequent changes in the expected cash flows associated with a future period's updated DCF analysis, however, are recorded as an increase to (or reversal of) credit loss expense with the offset recorded to the allowance. We charge write-offs against the allowance when: (i) we determine the recovery of amortized cost to be uncollectible based on our evaluation of the financial condition of the issuer; (ii) we have the intent, or requirement, to sell a security for which an allowance for credit losses was previously established; or (iii) we sold a security for which an allowance for credit losses was previously established. Accrued interest on fixed income securities and CMLs is recorded as a component of “Interest and dividends due or accrued” on our Consolidated Balance Sheet. If accrued interest is due but not paid within 90 days, we reverse the delinquent amount against investment income, which is a component of “Net investment income earned” on our Consolidated Statements of Income. We do not record a valuation allowance on our accrued interest balance as we reverse delinquent amounts on a timely basis. We consider a debt security to be past due at the time any principal or interest payments become 90 days delinquent. Commercial Mortgage Loans Beginning in 2020, our investment portfolio contains an allocation to CMLs. As of September 30, 2020, CMLs accounted for less than 1% of our invested assets. CMLs are loans secured by commercial property, such as an office building, multi-family apartment complex, industrial warehouse, or shopping center. We may acquire investments in CMLs through (i) direct originations under a loan syndication arrangement or (ii) a marketplace purchase. We record our investment in CMLs on the settlement date of the loan. Our CMLs are classified as held-for-investment and reported at amortized cost, net of the applicable allowance for credit losses, on our Consolidated Balance Sheet. We evaluate our CMLs for expected credit loss under the same DCF methodology described above for fixed income securities. The discount rate used in this DCF model is either (i) the effective interest rate implicit in the CML at the date of acquisition for fixed rate investments, or (ii) the effective interest rate in effect as of the reporting date for non-fixed-rate CMLs. The allowance for credit losses on our CML investments is calculated as the shortfall between amortized cost at the reporting date and the present value of future cash flows calculated in the DCF analysis. The treatment of earnings and the related classification of the expected credit losses on the Consolidated Statements of Income and the Consolidated Balance Sheet are consistent with our fixed income securities as described above. Allowance for Uncollectible Premiums Receivable We estimate an allowance for expected credit losses on our outstanding premiums receivable balance at each reporting date. In determining this allowance, we use a method that considers the aging of the receivable, based on the effective year of the related policy, along with our historical receivable loss experience. We also contemplate expected macroeconomic conditions over the expected collection period, which are short-term in nature because the majority of the balances are collected within a year or two of policy issuance. Expected credit losses on premiums receivable are charged to earnings as credit loss expense, which is a component of "Other insurance expenses" on our Consolidated Statements of Income, with an offsetting allowance recorded as a contra-asset reflected in the carrying value of the receivable. Subsequent changes in the allowance are recorded as an increase to (or reversal of) credit loss expense. We charge write-offs against the allowance when we determine the account to be uncollectible after considering information obtained from our collection efforts. Allowance for Uncollectible Reinsurance Recoverable The "Reinsurance recoverable" balance on our Consolidated Balance Sheets represents our estimate of amounts that will be recovered from reinsurers under our various treaties. Generally, amounts recoverable from reinsurers are recognized as assets at the same time and in a manner consistent with the paid and unpaid losses associated with the reinsured policies. We would consider a recoverable balance from a reinsurer to be past due if payment is not received by the first day following the invoice due date. We require collateral to secure reinsurance recoverable balances primarily from our reinsurance carriers that are not authorized, otherwise approved, or certified to do business in one or more of our ten insurance subsidiaries' domiciliary states. Our ten insurance subsidiaries are collectively referred to as the "Insurance Subsidiaries." This collateral is typically in the form of a letter of credit or cash. We estimate an allowance for expected credit losses on our outstanding reinsurance recoverable balance at each reporting date. Credit risk is mitigated to the extent we have obtained collateral. As part of our allowance calculation, we reduce the recoverable balance by the amount of the collateral. We then pool the uncollateralized balances by similar risk characteristics, including the financial strength rating of the reinsurer, and use a probability-of-default methodology to calculate the allowance. Historical default rates are sourced from AM Best and are coupled with severity assumptions in developing a baseline scenario. We then stress this scenario by incorporating forecasts of industry catastrophe losses and economic factors sourced through third-party data providers. In developing our best estimate of the allowance for credit losses, we consider our outlook as to the probability of each of these scenarios occurring.
Percent of commercial mortgage loans of our invested assets	1.00%

Accounting Pronouncements

Accounting Pronouncements - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Accounting Pronouncements	Adoption of Accounting Pronouncements In June 2016, the Financial Accounting Standards Board (“FASB”) issued ASU 2016-13, Financial Instruments - Credit Losses , and subsequent additional implementation guidance (collectively referred to as “ASU 2016-13”) that changes the way entities recognize impairment of financial assets. The new guidance requires immediate recognition of estimated credit losses expected to occur over the remaining life of many financial assets through the establishment of a valuation allowance. The valuation allowance is a measurement of expected losses based on relevant information about past events, including historical experience, current conditions, and reasonable and supportable forecasts that affect the collectability of the reported amount. Additionally, ASU 2016-03 requires the presentation of the impacted financial assets on the consolidated balance sheet net of the valuation allowance. We adopted this guidance on January 1, 2020, applied a modified retrospective approach for the adoption, and recorded a net cumulative-effect adjustment to increase the opening balance of 2020 retained earnings by $1.4 million, after tax. As prescribed in ASU 2016-13, we did not adjust the amortized cost basis of any securities for which we previously had recorded OTTI. The cumulative-effect increase to retained earnings represents the net adjustment required to (i) establish valuation allowances on our held-to-maturity ("HTM") debt securities and (ii) re-estimate valuation allowances on our premiums receivables and reinsurance recoverables under ASU 2016-13. See Note 1. "Basis of Presentation and Accounting Policies" of this Form 10-Q for accounting policy updates related to ASU 2016-13. Additionally, see Note 4. "Investments," Note 7. "Allowance for Uncollectible Premiums Receivable," and Note 8. "Reinsurance" of this Form 10-Q for additional information regarding credit losses related to the respective financial assets. In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement: Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement (“ASU 2018-13”). ASU 2018-13 modifies the disclosure requirements for fair value measurements by removing certain disclosures, and modifying and adding disclosure requirements. The additional disclosure requirements include (i) the change in unrealized gains and losses for the period included in other comprehensive income (“OCI”) for recurring Level 3 fair value measurements held at the end of the reporting period, and (ii) the range and weighted average of significant observable inputs used to develop Level 3 fair value measurements. We adopted the provisions related to removed disclosures in the fourth quarter of 2019 and adopted the remaining disclosure requirements in the first quarter of 2020. As it requires disclosure only, ASU 2018-13 has no impact on our financial condition or results of operations. In August 2018, the FASB issued ASU 2018-15, Intangibles - Goodwill and Other - Internal-Use Software: Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract (“ASU 2018-15”). ASU 2018-15 aligns the requirements for capitalizing implementation costs incurred in a cloud computing hosting service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. We adopted this guidance prospectively on January 1, 2020, and it did not have a material impact on our financial condition or results of operations. Pronouncements to be effective in the future In December 2019, the FASB issued ASU 2019-12, Income Taxes - Simplifying the Accounting for Income Taxes (“ASU 2019-12”). Among other items, ASU 2019-12 simplifies the accounting treatment of tax law changes and year-to-date losses in interim periods. An entity generally recognizes the effects of a change in tax law in the period of enactment; however, there is an exception for tax laws with delayed effective dates. Under current guidance, an entity may not adjust its annual effective tax rate for a tax law change until the period in which the law is effective. ASU 2019-12 provides that all effects of a tax law change, including adjustment of the estimated annual effective tax rate, are recognized in the period of enactment. For year-to-date losses in interim periods, an entity is required currently to estimate its annual effective tax rate for the full fiscal year at the end of each interim period and use that rate to calculate its income taxes on a year-to-date basis. When an interim period loss exceeds the anticipated loss for the year, the income tax benefit is limited to the amount that would be recognized if the year-to-date loss were the anticipated loss for the full year. ASU 2019-12 removes this limitation and an entity would compute its income tax benefit at each interim period based on its estimated annual effective tax rate. ASU 2019-12 is effective for fiscal years beginning after December 15, 2020, including interim periods within those annual periods. Early adoption is permitted. We are currently evaluating the impact of this guidance on our financial condition and results of operations. In March 2020, the FASB issued ASU 2020-04, Reference Rate Reform (Topic 848) - Facilitation of the Effects of Reference Rate Reform on Financial Reporting (“ASU 2020-04”). ASU 2020-04 provides optional expedients and exceptions to the guidance in GAAP on contract modifications and hedge accounting to ease the financial reporting burdens related to the expected market transition away from the London Interbank Offered Rate ("LIBOR") and other interbank offered rates to alternative reference rates. Companies can elect to adopt ASU 2020-04 as of the beginning of the interim period that includes March 2020, or any date thereafter through December 31, 2022. We are currently evaluating the impact of this guidance on our financial condition and results of operations.
Accounting Standards Update 2016-13 [Member] | Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption		$ 1,400

Statements of Cash Flows

Statements of Cash Flows	9 Months Ended
	Sep. 30, 2020
Supplemental Cash Flow Information [Abstract]
Statements of Cash Flows	Statements of Cash Flows Supplemental cash flow information was as follows: Nine Months ended September 30, ($ in thousands) 2020 2019 Cash paid during the period for: Interest $ 24,449 19,261 Federal income tax 34,000 42,000 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases 7,077 6,062 Operating cash flows from financing leases 13 12 Financing cash flows from finance leases 429 811 Non-cash items: Corporate actions related to fixed income securities, AFS 1 32,580 29,771 Corporate actions related to fixed income securities, HTM 1 2,596 — Corporate actions related to equity securities 1 890 14,250 Assets acquired under finance lease arrangements 119 824 Assets acquired under operating lease arrangements 22,104 13,648 Non-cash purchase of property and equipment 9 108 1 Examples of such corporate actions include exchanges, non-cash acquisitions, and stock splits. The following table provides a reconciliation of cash and restricted cash reported in the Consolidated Balance Sheets that equate to the amount reported in the Consolidated Statements of Cash Flows: ($ in thousands) September 30, 2020 December 31, 2019 Cash $ 785 300 Restricted cash 15,110 7,675 Total cash and restricted cash shown in the Statements of Cash Flows $ 15,895 7,975 Amounts included in restricted cash represent cash received from the National Flood Insurance Program ("NFIP"), which is restricted to pay flood claims under the Write Your Own program.

Investments

Investments	9 Months Ended
	Sep. 30, 2020
Investments [Abstract]
Investments	Investments (a) Information about our AFS securities as of September 30, 2020, and December 31, 2019, is as follows: September 30, 2020 ($ in thousands) Cost/ Allowance for Credit Losses Unrealized Unrealized Fair AFS fixed income securities: U.S. government and government agencies $ 110,201 — 7,374 (46) 117,529 Foreign government 15,679 (7) 1,336 — 17,008 Obligations of states and political subdivisions 1,152,794 (15) 78,841 (164) 1,231,456 Corporate securities 2,154,302 (5,358) 157,689 (7,802) 2,298,831 Collateralized loan obligations ("CLO") and other asset-backed securities ("ABS") 942,627 (1,121) 18,274 (14,198) 945,582 Residential mortgage-backed securities ("RMBS") 1,122,678 (647) 61,259 (333) 1,182,957 Commercial mortgage-backed securities ("CMBS") 599,692 (32) 46,386 (1,872) 644,174 Total AFS fixed income securities $ 6,097,973 (7,180) 371,159 (24,415) 6,437,537 December 31, 2019 ($ in thousands) Cost/ Unrealized Unrealized Fair AFS fixed income securities: U.S. government and government agencies $ 112,680 3,506 — 116,186 Foreign government 18,011 533 (2) 18,542 Obligations of states and political subdivisions 1,168,185 62,175 (270) 1,230,090 Corporate securities 1,866,881 81,906 (1,310) 1,947,477 CLO and other ABS 790,517 7,929 (5,434) 793,012 RMBS 1,409,003 43,421 (455) 1,451,969 CMBS 514,709 23,902 (267) 538,344 Total AFS fixed income securities $ 5,879,986 223,372 (7,738) 6,095,620 The following tables provide a roll forward of the allowance for credit losses on our AFS fixed income securities for the periods indicated: Quarter ended September 30, 2020 ($ in thousands) Beginning Balance Current Provision for Securities without Prior Allowance Increase (Decrease) on Securities with Prior Allowance, excluding intent (or Requirement) to Sell Securities Reductions for Securities Sold Reductions for Securities Identified as Intent (or Requirement) to Sell during the Period Ending Balance Foreign government $ 28 — (2) (19) — 7 Obligations of states and political subdivisions 17 9 (11) — — 15 Corporate securities 8,077 1,016 (3,455) (265) (15) 5,358 CLO and other ABS 1,389 — (210) (51) (7) 1,121 RMBS 831 — (157) (27) — 647 CMBS 53 — (21) — — 32 Total AFS fixed income securities $ 10,395 1,025 (3,856) (362) (22) 7,180 Nine Months ended September 30, 2020 ($ in thousands) Beginning Balance Current Provision for Securities without Prior Allowance Increase (Decrease) on Securities with Prior Allowance, excluding intent (or Requirement) to Sell Securities Reductions for Securities Sold Reductions for Securities Identified as Intent (or Requirement) to Sell during the Period Ending Balance Foreign government $ — 26 — (19) — 7 Obligations of states and political subdivisions — 15 — — — 15 Corporate securities — 6,100 — (659) (83) 5,358 CLO and other ABS — 1,237 — (109) (7) 1,121 RMBS — 690 — (43) — 647 CMBS — 32 — — — 32 Total AFS fixed income securities $ — 8,100 — (830) (90) 7,180 During 2020, we neither experienced any write-offs or recoveries of our AFS fixed income securities nor purchased any assets with credit deterioration, so these items are not included in the table above. As disclosed in Note 1. "Basis of Presentation and Accounting Policies," we do not evaluate accrued interest on our AFS securities for credit impairment as we write-off these balances in a timely manner. As of September 30, 2020, accrued interest on AFS securities amounted to $45.3 million and we did not record any write-offs of accrued interest during 2020. (b) Quantitative information about unrealized losses on our AFS portfolio is provided below. September 30, 2020 Less than 12 months 12 months or longer Total ($ in thousands) Fair Value Unrealized Fair Value Unrealized Fair Value Unrealized AFS fixed income securities: U.S. government and government agencies $ 4,855 (46) — — 4,855 (46) Obligations of states and political subdivisions 15,929 (164) — — 15,929 (164) Corporate securities 100,989 (7,444) 2,695 (358) 103,684 (7,802) CLO and other ABS 302,492 (7,804) 149,893 (6,394) 452,385 (14,198) RMBS 55,128 (300) 2,316 (33) 57,444 (333) CMBS 80,308 (1,320) 14,342 (552) 94,650 (1,872) Total AFS fixed income securities $ 559,701 (17,078) 169,246 (7,337) 728,947 (24,415) December 31, 2019 Less than 12 months 12 months or longer Total ($ in thousands) Fair Unrealized Fair Value Unrealized Fair Value Unrealized AFS fixed income securities: Foreign government $ 1,416 (2) — — 1,416 (2) Obligations of states and political subdivisions 35,838 (270) — — 35,838 (270) Corporate securities 84,832 (480) 20,182 (830) 105,014 (1,310) CLO and other ABS 205,191 (1,938) 204,385 (3,496) 409,576 (5,434) RMBS 126,089 (425) 5,375 (30) 131,464 (455) CMBS 62,893 (264) 828 (3) 63,721 (267) Total AFS fixed income securities $ 516,259 (3,379) 230,770 (4,359) 747,029 (7,738) We currently do not intend to sell any of the securities in the tables above, nor is it likely we will be required to sell any of them. After considering these factors and our review of these securities under our methodology for analyzing OTTI, we have concluded that they are temporarily impaired because we believe (i) they will mature at par value, (ii) they have not incurred a credit impairment, and (iii) future values of these securities will fluctuate with changes in interest rates. This conclusion reflects our current judgment as to the financial position and future prospects of the entity that issued the investment security and underlying collateral. The COVID-19-related governmental orders have caused uncertainty and volatility in the financial markets. While market conditions improved during Third Quarter 2020, gross unrealized losses on our AFS fixed income securities portfolio increased to $24.4 million at September 30, 2020, from $7.7 million at December 31, 2019. This increase was driven by widening credit spreads as a result of the uncertainty in the marketplace, and was partially offset by a significant decline in benchmark United States Treasury rates. (c) Fixed income securities at September 30, 2020, are shown below by contractual maturity. Mortgage-backed securities are included in the maturity tables using the estimated average life of each security. Expected maturities may differ from contractual maturities because issuers may have the right to call or prepay obligations, with or without call or prepayment penalties. AFS HTM ($ in thousands) Fair Value Carrying Value Fair Value Due in one year or less $ 336,142 1,456 1,490 Due after one year through five years 3,714,414 15,131 16,293 Due after five years through 10 years 1,960,132 2,500 2,430 Due after 10 years 426,849 — — Total fixed income securities $ 6,437,537 19,087 20,213 (d) The following table summarizes our other investment portfolio by strategy: Other Investments September 30, 2020 December 31, 2019 ($ in thousands) Carrying Value Remaining Commitment Maximum Exposure to Loss 1 Carrying Value Remaining Commitment Maximum Exposure to Loss 1 Alternative Investments Private equity $ 146,810 110,173 256,983 118,352 93,138 211,490 Private credit 49,254 96,131 145,385 42,532 105,340 147,872 Real assets 21,859 19,070 40,929 23,256 20,741 43,997 Total alternative investments 217,923 225,374 443,297 184,140 219,219 403,359 Other securities 40,725 — 40,725 32,667 — 32,667 Total other investments $ 258,648 225,374 484,022 216,807 219,219 436,026 1 The maximum exposure to loss includes both the carry value of these investments and the related remaining commitments. In addition, tax credits that have been previously recognized in Other securities are subject to the risk of recapture, which we do not consider significant. We are contractually committed to make additional investments up to the remaining commitments stated above; but we do not have a future obligation to fund losses or debts on behalf of these investments. We have not provided any non-contractual financial support at any time during 2020 or 2019. The following table shows gross summarized financial information for our other investments portfolio, including the portion we do not own. The majority of these investments are carried under the equity method of accounting and report results to us on a one-quarter lag. The following table provides (i) the gross summarized financial statement information for these investments for the three-month and nine-month periods ended June 30, and (ii) the portion of these results that are included in our Third Quarter results: Income Statement Information Quarter ended September 30, Nine Months ended September 30, ($ in millions) 2020 2019 2020 2019 Net investment (loss) income $ 83.4 (14.0) 92.9 10.1 Realized (losses) gains 731.3 121.1 1,075.0 370.4 Net change in unrealized appreciation (depreciation) 2,230.4 1,739.4 571.6 4,517.4 Net income $ 3,045.1 1,846.5 1,739.5 4,897.9 Insurance Subsidiaries’ alternative investments income $ 18.7 5.2 8.9 13.0 As noted above, the majority of our alternative investments report their results to us on a one-quarter lag, so the $18.7 million of gains in the table above reflects the improvement in the financial markets during the second quarter of 2020. (e) Certain Insurance Subsidiaries, as members of the Federal Home Loan Bank of Indianapolis ("FHLBI") and the Federal Home Loan Bank of New York ("FHLBNY"), have pledged certain AFS fixed income securities as collateral. To comply with insurance laws, certain Insurance Subsidiaries also had certain securities deposited with various state and regulatory agencies at September 30, 2020. We retain all rights regarding all securities pledged as collateral. The following table summarizes the market value of these securities at September 30, 2020: ($ in millions) FHLBI Collateral FHLBNY Collateral State and Total U.S. government and government agencies $ — — 22.7 22.7 Obligations of states and political subdivisions — — 5.1 5.1 RMBS 133.0 205.2 — 338.2 CMBS 7.2 36.7 — 43.9 Total pledged as collateral $ 140.2 241.9 27.8 409.9 (f) We did not have exposure to any credit concentration risk of a single issuer greater than 10% of our stockholders' equity, other than certain U.S. government-backed investments, as of September 30, 2020, or December 31, 2019. (g) The components of pre-tax net investment income earned were as follows: Quarter ended September 30, Nine Months ended September 30, ($ in thousands) 2020 2019 2020 2019 Fixed income securities $ 51,285 50,749 152,617 150,689 CMLs 245 — 463 — Equity securities 1,948 1,885 5,523 5,265 Short-term investments 244 1,410 1,830 5,213 Other investments 18,671 5,267 9,167 13,421 Investment expenses (4,208) (3,485) (11,004) (9,639) Net investment income earned $ 68,185 55,826 158,596 164,949 The increase in net investment income earned in Third Quarter 2020 compared to Third Quarter 2019 was driven by our alternative investments in our other investments portfolio, and reflect the improvement in the equity markets from the second quarter of 2020, as our results on these holdings are recorded on a one-quarter lag. The decrease in net investment income earned Nine Months 2020 compared to Nine Months 2019 was driven by our alternative investments within our other investments portfolio, and reflects deterioration in the equity markets related to the financial market volatility that existed in the year due to COVID-19. (h) The following table summarizes OTTI by asset type for the periods indicated: Quarter ended September 30, 2020 2019 ($ in thousands) Credit Loss Other Impairment Expense Recognized in Earnings Recognized in Earnings HTM fixed income securities: Corporate securities $ 3 — 3 — Total HTM fixed income securities 3 — 3 — AFS fixed income securities: Foreign government 3 — 3 — Obligations of states and political subdivisions 2 — 2 — Corporate securities 2,454 — 2,454 (1,681) CLO and other ABS 217 (44) 173 — RMBS 157 — 157 — CMBS 21 — 21 — Total AFS fixed income securities 2,854 (44) 2,810 (1,681) CMLs (2) — (2) — Short term investments (1) — (1) — Other investments — — — (610) Total OTTI benefit (expense) $ 2,854 (44) 2,810 (2,291) Nine Months ended September 30, 2020 2019 ($ in thousands) Credit Loss (Expense) Benefit Other Impairment Expense Recognized in Earnings Recognized in Earnings HTM fixed income securities: Corporate securities $ 4 — 4 — Total HTM fixed income securities 4 — 4 — AFS fixed income securities: U.S. government and government agencies — (14) (14) — Foreign government (25) — (25) — Obligations of states and political subdivisions (15) (62) (77) (65) Corporate securities (6,018) (12,103) (18,121) (2,455) CLO and other ABS (1,230) (2,137) (3,367) — RMBS (690) (91) (781) — CMBS (32) (1,852) (1,884) — Total AFS fixed income securities (8,010) (16,259) (24,269) (2,520) CMLs (220) — (220) — Short-term investments (1) — (1) — Other investments — — — (846) Total OTTI expense $ (8,227) (16,259) (24,486) (3,366) OTTI amounted to $24.5 million in Nine Months 2020 and included $16.3 million of impairments on securities we intended to sell to provide our investment managers flexibility to trade and optimize our investment portfolio in the COVID-19-related market volatility and uncertainty. The remaining $8.2 million of OTTI in Nine Months 2020 related to our allowance for credit losses and included an approximate $2.9 million reduction of this allowance in Third Quarter 2020 from improving market conditions during the quarter as compared to June 30, 2020. (i) Net realized and unrealized gains and losses (excluding OTTI) for Third Quarter 2020 and 2019 included the following: Quarter ended September 30, Nine Months ended September 30, ($ in thousands) 2020 2019 2020 2019 Net realized gains (losses) on the disposals of securities: Fixed income securities $ 561 (1,141) 7,137 2,063 CMLs 1 — 2 — Equity securities — 21,602 (3) 24,733 Short-term investments 11 (36) 157 (21) Other investments — — (5) (23) Net realized gains (losses) on the disposal of securities 573 20,425 7,288 26,752 OTTI benefit (expense) 2,810 (2,291) (24,486) (3,366) Net realized gains (losses) 3,383 18,134 (17,198) 23,386 Unrealized gains (losses) recognized in income on equity securities 4,338 (20,317) (7,098) (8,091) Total net realized and unrealized investment gains (losses) $ 7,721 (2,183) $ (24,296) 15,295 During Third Quarter 2020, the $9.9 million increase in net realized and unrealized investment gains was primarily driven by the improvements in the allowance for credit losses on our AFS fixed income securities as discussed above. Excluding OTTI, realized and unrealized gains and losses were impacted in Third Quarter 2020 by improvements in market conditions that resulted in unrealized gains on our equity portfolio. In the comparable quarter last year, we sold a significant portion of our public equity securities, realizing net gains of $21.6 million. These realized gains were substantially offset by the reversal of previously-recorded unrealized gains related to the securities sold, which accounted for $21.4 million of the $20.3 million reduction in the table above. For Nine Months 2020, net realized and unrealized investment losses were $24.3 million, compared to net gains of $15.3 million for Nine Months 2019. This fluctuation was driven by the increase in OTTI expense discussed above, coupled with the decrease in realized gains on the disposal of securities, which were higher last year due to the referenced public equity sales. Unrealized gains (losses) recognized in income on equity securities, as reflected in the table above, include the following: Quarter ended September 30, Nine Months ended September 30, ($ in thousands) 2020 2019 2020 2019 Unrealized gains (losses) recognized in income on equity securities: On securities remaining in our portfolio at September 30, 2020 $ 4,338 1,109 (7,101) 1,805 On securities sold in each respective period — (21,426) 3 (9,896) Total unrealized gains (losses) recognized in income on equity securities $ 4,338 (20,317) (7,098) (8,091) The components of net realized gains on disposals of securities for the periods indicated were as follows: Quarter ended September 30, Nine Months ended September 30, ($ in thousands) 2020 2019 2020 2019 HTM fixed income securities Gains $ 1 — 2 1 Losses — — — (15) AFS fixed income securities Gains 2,955 1,078 14,770 5,565 Losses (2,395) (2,219) (7,635) (3,488) CMLs Gains 1 — 2 — Losses — — — — Equity securities Gains — 21,630 — 24,868 Losses — (28) (3) (135) Short-term investments Gains 18 2 355 18 Losses (7) (38) (198) (39) Other investments Gains — — — 7 Losses — — (5) (30) Total net realized gains on disposals of securities $ 573 20,425 7,288 26,752 Realized gains and losses on the sale of investments are determined on the basis of the cost of the specific investments sold.

Indebtedness

Indebtedness	9 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Indebtedness	Indebtedness The table below provides a summary of our outstanding debt at September 30, 2020, and December 31, 2019: Outstanding Debt Issuance Date Maturity Date Interest Rate Original Amount 2020 Carry Value ($ in thousands) Unamortized Issuance Costs Debt Discount September 30, 2020 December 31, 2019 Description Short-term Issuance: FHLBNY 9/14/2020 11/16/2020 0.36 % 100,000 — — 100,000 — FHLBI 3/19/2020 12/14/2020 0.58 % 67,000 — — 67,000 — Total short-term debt — — 167,000 — Other Outstanding: FHLBI 12/16/2016 12/16/2026 3.03 % 60,000 — — 60,000 60,000 FHLBNY 8/15/2016 8/16/2021 1.56 % 25,000 — — 25,000 25,000 FHLBNY 7/21/2016 7/21/2021 1.61 % 25,000 — — 25,000 25,000 Senior Notes 11/3/2005 11/1/2035 6.70 % 100,000 329 505 99,166 99,125 Senior Notes 11/16/2004 11/15/2034 7.25 % 50,000 170 87 49,743 49,725 Senior Notes 3/1/2019 3/1/2049 5.375 % 300,000 2,986 5,781 291,233 291,010 Finance lease obligations 424 737 Total long-term debt 3,485 6,373 550,566 550,597 Total debt 3,485 6,373 717,566 550,597 Our long-term debt balance was level with December 31, 2019. We, however, increased our short-term debt by $302 million during the first quarter of 2020 as a contingency in light of the COVID-19-related volatility and uncertainty in the financial markets. We repaid the $50 million line of credit in May 2020, and the $85 million FHLBNY borrowing in September 2020. The remaining $167 million short-term borrowings are still outstanding as of September 30, 2020. The proceeds from these short-term borrowings were invested in high-quality money market funds, and for the most part, were made to increase liquidity and operating flexibility. Our short-term borrowings through Nine Months 2020 consisted of the following: • On February 18, 2020, Selective Insurance Company of America (“SICA”) borrowed short-term funds of $85 million from the FHLBNY at an interest rate of 1.81%. This borrowing was refinanced upon its maturity on March 18, 2020, at a lower interest rate of 0.68%. This borrowing was repaid on September 18, 2020. • On March 12, 2020, SICA borrowed $100 million from the FHLBNY at an interest rate of 0.78%. This borrowing was refinanced upon its maturity on September 14, 2020, at a lower interest rate of 0.36%. This borrowing matures on November 16, 2020. • On March 19, 2020, Selective Insurance Company of South Carolina ("SISC") and Selective Insurance Company of the Southeast ("SISE") borrowed $39 million and $28 million, respectively, from the FHLBI at an interest rate of 0.58%. These borrowings mature on December 14, 2020. • On March 24, 2020, the Parent borrowed $50 million on its line of credit issued by the Bank of Montreal at an interest rate of 2.244%. This borrowing was repaid on May 8, 2020. The remaining $167 million in short-term borrowings are contractually due in the fourth quarter of 2020, and we expect to repay them by year-end. As of September 30, 2020, we were compliant with our required financial debt covenants under the line of credit. For additional information on our indebtedness and debt covenants, see Note 10. "Indebtedness" in Item 8. "Financial Statements and Supplementary Data." of our 2019 Annual Report.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements We primarily measure the financial assets in our investment portfolio at fair value as disclosed on the Consolidated Balance Sheets. The following table presents the carrying amounts and estimated fair values of our financial liabilities as of September 30, 2020, and December 31, 2019: September 30, 2020 December 31, 2019 ($ in thousands) Carrying Amount Fair Value Carrying Amount Fair Value Financial Liabilities Short-term debt: 0.36% Borrowings from FHLBNY $ 100,000 100,005 — — 0.58% Borrowings from FHLBI 67,000 67,050 — — Total short-term debt 167,000 167,055 — — Long-term debt: 7.25% Senior Notes 49,913 67,350 49,910 66,365 6.70% Senior Notes 99,495 130,651 99,480 123,104 5.375% Senior Notes 294,219 365,756 294,157 357,025 1.61% borrowings from FHLBNY 25,000 25,255 25,000 24,901 1.56% borrowings from FHLBNY 25,000 25,269 25,000 24,875 3.03% borrowings from FHLBI 60,000 67,972 60,000 63,002 Subtotal long-term debt 553,627 682,253 553,547 659,272 Unamortized debt issuance costs (3,485) (3,687) Finance lease obligations 424 737 Total long-term debt $ 550,566 550,597 For more information about our short-term borrowings, refer to Note 5. "Indebtedness." For a discussion of the fair value hierarchy and techniques used to value our financial assets and liabilities, refer to Note 2. "Summary of Significant Accounting Policies" in Item 8. "Financial Statements and Supplementary Data." of our 2019 Annual Report. The following tables provide quantitative disclosures of our financial assets that were measured and recorded at fair value at September 30, 2020, and December 31, 2019: September 30, 2020 Fair Value Measurements Using ($ in thousands) Assets Quoted Prices in 1 Significant Other Observable Inputs (Level 2) 1 Significant Unobservable Description Measured on a recurring basis: AFS fixed income securities: U.S. government and government agencies $ 117,529 43,287 74,242 — Foreign government 17,008 — 17,008 — Obligations of states and political subdivisions 1,231,456 — 1,228,602 2,854 Corporate securities 2,298,831 — 2,261,195 37,636 CLO and other ABS 945,582 — 900,862 44,720 RMBS 1,182,957 — 1,182,957 — CMBS 644,174 — 644,174 — Total AFS fixed income securities 6,437,537 43,287 6,309,040 85,210 Equity securities: Common stock 1 150,153 103,603 — — Preferred stock 1,671 1,671 — — Total equity securities 151,824 105,274 — — Short-term investments 380,890 379,317 1,573 — Total assets measured at fair value $ 6,970,251 527,878 6,310,613 85,210 December 31, 2019 Fair Value Measurements Using ($ in thousands) Assets Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) 1 Significant Other Observable Inputs (Level 2) 1 Significant Unobservable Description Measured on a recurring basis: AFS fixed income securities: U.S. government and government agencies $ 116,186 41,083 75,103 — Foreign government 18,542 — 18,542 — Obligations of states and political subdivisions 1,230,090 — 1,230,090 — Corporate securities 1,947,477 — 1,930,426 17,051 CLO and other ABS 793,012 3,635 772,343 17,034 RMBS 1,451,969 — 1,451,969 — CMBS 538,344 — 538,344 — Total AFS fixed income securities 6,095,620 44,718 6,016,817 34,085 Equity securities: Common stock 1 69,900 32,145 — — Preferred stock 3,037 3,037 — — Total equity securities 72,937 35,182 — — Short-term investments 282,490 265,306 17,184 — Total assets measured at fair value $ 6,451,047 345,206 6,034,001 34,085 1 Investments amounting to $46.6 million at September 30, 2020, and $37.8 million at December 31, 2019, were measured at fair value using net asset value per share (or its practical expedient) and are not classified in the fair value hierarchy. These investments are not redeemable and the timing of liquidations of the underlying assets is unknown at each reporting period. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to total assets measured at fair value. The following table provides a summary of Level 3 changes in Nine Months 2020 and Nine Months 2019: September 30, 2020 ($ in thousands) Obligations of states and political subdivisions Corporate Securities CLO and Other ABS Total Fair value, December 31, 2019 — 17,051 17,034 34,085 Total net (losses) gains for the period included in: OCI (36) (2,415) 732 (1,719) Net realized and unrealized (losses) gains — (456) (247) (703) Net investment income earned — — 3 3 Purchases — 19,002 11,751 30,753 Sales — — — — Issuances — — — — Settlements — (138) (1,030) (1,168) Transfers into Level 3 2,890 4,592 26,401 33,883 Transfers out of Level 3 — — (9,924) (9,924) Fair value, September 30, 2020 2,854 37,636 44,720 85,210 Change in unrealized (losses) gains for the period included in earnings for assets held at period end — (456) (247) (703) Change in unrealized gains (losses) for the period included in OCI for assets held at period end (36) (2,415) 732 (1,719) September 30, 2019 ($ in thousands) Corporate Securities CLO and Other ABS Total Fair value, December 31, 2018 — 7,409 7,409 Total net (losses) gains for the period included in: OCI (69) (14) (83) Net investment income earned — 244 244 Purchases — 18,404 18,404 Sales — — — Issuances — — — Settlements — (105) (105) Transfers into Level 3 16,419 13,603 30,022 Transfers out of Level 3 — (19,662) (19,662) Fair value, September 30, 2019 16,350 19,879 36,229 Change in unrealized gains (losses) for the period included in earnings for assets held at period end — — — The following tables provide quantitative information regarding our financial assets and liabilities that were disclosed at fair value at September 30, 2020, and December 31, 2019: September 30, 2020 Fair Value Measurements Using ($ in thousands) Assets/ Quoted Prices in Significant Other Significant Financial Assets HTM: Obligations of states and political subdivisions $ 4,849 — 4,849 — Corporate securities 15,364 — 15,364 — Total HTM fixed income securities $ 20,213 — 20,213 — CMLs $ 30,595 — 2,540 28,055 Financial Liabilities Short-term debt: 0.36% Borrowings from FHLBNY $ 100,005 — 100,005 — 0.58% Borrowings from FHLBI 67,050 — 67,050 — Total short-term debt $ 167,055 — 167,055 — Long-term debt: 7.25% Senior Notes $ 67,350 — 67,350 — 6.70% Senior Notes 130,651 — 130,651 — 5.375% Senior Notes 365,756 — 365,756 — 1.61% borrowings from FHLBNY 25,255 — 25,255 — 1.56% borrowings from FHLBNY 25,269 — 25,269 — 3.03% borrowings from FHLBI 67,972 — 67,972 — Total long-term debt $ 682,253 — 682,253 — December 31, 2019 Fair Value Measurements Using ($ in thousands) Assets/ Quoted Prices in Significant Other Significant Financial Assets HTM: Obligations of states and political subdivisions $ 4,921 — 4,921 — Corporate securities 17,054 — 17,054 — Total HTM fixed income securities $ 21,975 — 21,975 — Financial Liabilities Long-term debt: 7.25% Senior Notes $ 66,365 — 66,365 — 6.70% Senior Notes 123,104 — 123,104 — 5.375% Senior Notes 357,025 — 357,025 — 1.61% borrowings from FHLBNY 24,901 — 24,901 — 1.56% borrowings from FHLBNY 24,875 — 24,875 — 3.03% borrowings from FHLBI 63,002 — 63,002 — Total long-term debt $ 659,272 — 659,272 —

Allowance for Uncollectible Pre

Allowance for Uncollectible Premiums Receivable (Notes)	9 Months Ended
	Sep. 30, 2020
Premiums Receivable [Abstract]
Allowance for Uncollectible Premiums Receivable Note [Text Block]	Premiums Receivable The following table provides a roll forward of the allowance for credit losses on our premiums receivable balance for the periods indicated: ($ in thousands) Quarter ended September 30, 2020 Nine Months ended September 30, 2020 Balance at beginning of period $ 21,000 $ 6,400 Cumulative effect adjustment 1 — 1,058 Balance at beginning of period, as adjusted $ 21,000 $ 7,458 Current period provision for expected credit losses 802 16,369 Write-offs charged against the allowance for credit losses (996) (3,272) Recoveries 194 445 Allowance for credit losses, end of period $ 21,000 $ 21,000 1 See Note 2. "Adoption of Accounting Pronouncements" above for additional information regarding our adoption of ASU 2016-13. In Nine Months 2020, we recognized an additional allowance for credit losses of $13.5 million, net of write-offs and recoveries. We based this increase on an evaluation of the recoverability of our premiums receivable in light of (i) the billing accommodations we announced during the first quarter of 2020, and (ii) the impact of certain state regulations that provided for deferral of payments without cancellation for a period up to 90 days and increased earned but uncollected premiums. The billing accommodations included individualized payment flexibility and suspending the effect of policy cancellations, late payment notices, and late or reinstatement fees.

Reinsurance

Reinsurance	3 Months Ended
	Jun. 30, 2020
Reinsurance Disclosures [Abstract]
Reinsurance	Reinsurance We evaluate and monitor the financial condition of our reinsurers under voluntary reinsurance arrangements to minimize our exposure to significant losses from reinsurer insolvencies. The following table provides (i) a disaggregation of our reinsurance recoverable balance by financial strength rating, and (ii) an aging analysis of our past due reinsurance recoverable balances as of September 30, 2020: September 30, 2020 ($ in thousands) Current Past Due Total Reinsurance Recoverables Financial strength rating of rated reinsurers 1 A++ $ 23,497 $ 230 $ 23,727 A+ 251,341 3,102 254,443 A 103,560 1,569 105,129 A- 115,196 — 115,196 B++ 95 288 383 B+ 10 — 10 Total rated reinsurers $ 493,699 $ 5,189 $ 498,888 Non-rated reinsurers Federal and state pools $ 111,399 $ — $ 111,399 Other than federal and state pools 2,919 81 3,000 Total non-rated reinsurers $ 114,318 $ 81 $ 114,399 Total reinsurance recoverable, gross $ 608,017 $ 5,270 $ 613,287 Less: allowance for credit losses 2 (1,831) Total reinsurance recoverable, net $ 611,456 1 Credit ratings as of September 30, 2020. 2 Represents our current expectation of credit losses on total current and past due reinsurance recoverables, and is not identifiable by reinsurer. We evaluate our estimate of expected credit losses through the methodology outlined in Note 1. “Basis of Presentation and Accounting Policies” above. The following table provides a rollforward of the allowance for credit losses on our reinsurance recoverable balance for the periods indicated: ($ in thousands) Quarter ended September 30, 2020 Nine Months ended September 30, 2020 Balance at beginning of period $ 2,396 $ 4,400 Cumulative effect adjustment 1 — (2,903) Balance at beginning of period, as adjusted $ 2,396 $ 1,497 Current period provision for expected credit losses (565) 334 Write-offs charged against the allowance for credit losses — — Recoveries — — Allowance for credit losses, end of period $ 1,831 $ 1,831 1 See Note 2. "Adoption of Accounting Pronouncements" for additional information regarding our adoption of ASU 2016-13. The following table contains a listing of direct, assumed, and ceded reinsurance amounts for premiums written, premiums earned, and loss and loss expenses incurred for the periods indicated. For more information concerning reinsurance, refer to Note 8. “Reinsurance” in Item 8. “Financial Statements and Supplementary Data.” of our 2019 Annual Report. Quarter ended September 30, Nine Months ended September 30, ($ in thousands) 2020 2019 2020 2019 Premiums written: Direct $ 839,275 785,680 $ 2,420,350 2,359,441 Assumed 5,450 6,882 17,902 18,770 Ceded (125,217) (115,634) (346,665) (326,939) Net $ 719,508 676,928 $ 2,091,587 2,051,272 Premiums earned: Direct $ 803,957 752,872 $ 2,292,495 2,221,257 Assumed 6,147 6,356 18,375 18,660 Ceded (115,563) (105,608) (333,955) (311,105) Net $ 694,541 653,620 $ 1,976,915 1,928,812 Loss and loss expenses incurred: Direct $ 530,192 437,617 $ 1,407,000 1,297,975 Assumed 4,232 4,362 13,430 13,975 Ceded (86,622) (43,304) (168,355) (145,712) Net $ 447,802 398,675 $ 1,252,075 1,166,238 Direct premiums written ("DPW") increased in Third Quarter 2020 and Nine Months 2020 compared to Third Quarter 2019 and Nine Months 2019, respectively. Nine Months 2020 was reduced by a $75 million return audit and mid-term endorsement premium accrual recorded during the first quarter of 2020. This accrual reflects a premium reduction due to lower payroll and sales exposures on the workers compensation and general liability lines of business resulting from the economic impacts of the COVID-19 pandemic. In addition, DPW for Nine Months 2020 was reduced by a $19.7 million premium credit to our personal and commercial automobile policyholders. Because of the unprecedented nature of the COVID-19-related governmental directives and the associated expected short-term favorable claims frequency impact, we obtained regulatory approval during April to provide this premium credit to our personal and commercial automobile customers. The premium credit to customers with in-force policies was equivalent to 15% of their April and May premiums. The $19.7 million of personal and commercial auto premium actions impacted DPW and direct premiums earned. Because lower exposures drove the reduction in premium, there was a reduction in direct loss and loss expenses incurred. The reduction in direct loss and loss expenses incurred for the premium credit was $13.3 million in casualty lines and $6.4 million in non-catastrophe property losses. Direct loss and loss expenses in Nine Months 2020 were impacted by $10.0 million in ultimate net losses estimated and recorded in the first quarter of 2020 for losses related to a small portion of our policies that provide a $25,000 sub-limited coverage for specified extra expenses to clean or disinfect a property when ordered by a Board of Health. COVID-19 Impact Quarter ended September 30, 2020 Nine Months ended September 30, 2020 ($ in thousands) Premium Audit Premium Credit Total Premium Audit Property Premium Credit Total DPW $ — — — $ (75,000) — (19,740) (94,740) Direct premiums earned (16,303) — (16,303) (64,636) — (19,740) (84,376) Direct loss and loss expenses incurred (9,468) — (9,468) (37,541) 10,000 (19,740) (47,281) Direct and ceded loss and loss expenses incurred in Third Quarter and Nine Months 2020 also were impacted by increased catastrophe losses, due to the severity of the storms and individual claims that met the retention of our property excess of loss treaty. Catastrophe losses were $79.5 million in Third Quarter 2020, compared to $24.2 million in Third Quarter 2019, and $195.9 million in Nine Months 2020, compared to $74.5 million in Nine Months 2019. Ceded premiums written, ceded premiums earned, and ceded loss and loss expenses incurred related to our participation in the NFIP, to which we cede 100% of our flood premiums, losses, and loss expenses are as follows: Ceded to NFIP Quarter ended September 30, Nine Months ended September 30, ($ in thousands) 2020 2019 2020 2019 Ceded premiums written $ (77,318) (74,863) $ (213,592) (206,451) Ceded premiums earned (68,427) (65,846) (202,656) (191,914) Ceded loss and loss expenses incurred (48,132) (27,459) (66,219) (62,208)

Reserve for Loss and Loss Expen

Reserve for Loss and Loss Expense	9 Months Ended
	Sep. 30, 2020
Insurance Loss Reserves [Abstract]
Reserve for Loss and Loss Expense	Reserve for Loss and Loss Expense The table below provides a roll forward of reserve for loss and loss expense balances: Nine Months ended September 30, ($ in thousands) 2020 2019 Gross reserve for loss and loss expense, at beginning of year $ 4,067,163 3,893,868 Less: reinsurance recoverable on unpaid loss and loss expense, at beginning of year 1 547,066 537,388 Net reserve for loss and loss expense, at beginning of year 3,520,097 3,356,480 Incurred loss and loss expense for claims occurring in the: Current year 1,295,285 1,200,878 Prior years (43,210) (34,640) Total incurred loss and loss expense 1,252,075 1,166,238 Paid loss and loss expense for claims occurring in the: Current year 421,981 384,436 Prior years 646,974 631,589 Total paid loss and loss expense 1,068,955 1,016,025 Net reserve for loss and loss expense, at end of period 3,703,217 3,506,693 Add: Reinsurance recoverable on unpaid loss and loss expense, at end of period 590,059 548,938 Gross reserve for loss and loss expense at end of period $ 4,293,276 4,055,631 1 Includes an adjustment of $2.9 million related to our adoption of ASU 2016-13. Refer to Note 2. "Adoption of Accounting Pronouncements" for additional information. Our current year incurred losses of $1,295.3 million were impacted by catastrophe losses that were $195.9 million in Nine Months 2020, compared to $74.5 million in Nine Months 2019. In addition, the current year incurred losses include ultimate net losses of $10.0 million for COVID-19-related losses related to a small portion of our policies that provide a $25,000 sub-limited coverage for specified extra expenses to clean or disinfect a property when ordered by a Board of Health. As of September 30, 2020, we have not incurred losses related to this exposure and the $10.0 million in ultimate net losses remains all IBNR. In most instances COVID-19 does not cause a direct physical loss to property, so we do not expect material business interruption losses from COVID-19 given the terms, conditions, and exclusions of our policies. Our practice has been to include or attach to all standard lines commercial property and businessowners policies an exclusion that states that all loss or property damage caused by or resulting from any virus, bacterium, or other microorganism that induces or is capable of inducing physical distress, illness, or disease is not a covered cause of loss. Prior year reserve development in Nine Months 2020 was favorable by $43.2 million, which included $50.0 million of casualty reserve development that was partially offset by $6.8 million of unfavorable property reserve development. The favorable casualty reserve development included $40.0 million of development in our workers compensation lines of business and $20.0 million in our general liability line of business, partially offset by $10.0 million of unfavorable reserve development in our commercial automobile line of business.

Segment Information

Segment Information	9 Months Ended
	Sep. 30, 2020
Segment Reporting [Abstract]
Segment Information	Segment Information We evaluate the results of our four reportable segments as follows: • Our Standard Commercial Lines, Standard Personal Lines, and E&S Lines are evaluated on before and after-tax underwriting results (net premiums earned, incurred loss and loss expense, policyholder dividends, policy acquisition costs, and other underwriting expenses), return on equity ("ROE") contribution, and combined ratios. • Our Investments segment is primarily evaluated on after-tax net investment income and its ROE contribution. After-tax net realized and unrealized gains and losses, which are not included in non-GAAP operating income, are also included in our Investment segment results. In computing each segment's results, we do not make adjustments for interest expense or corporate expenses. No segment has a separate investment portfolio or allocated assets. The following summaries present revenues (net investment income and net realized and unrealized gains and losses on investments for the Investments segment) and pre-tax income for the individual segments: Revenue by Segment Quarter ended September 30, Nine Months ended September 30, ($ in thousands) 2020 2019 2020 2019 Standard Commercial Lines: Net premiums earned: Commercial automobile $ 160,937 141,182 449,162 408,706 Workers compensation 75,595 75,478 204,207 232,657 General liability 181,459 169,084 509,312 495,402 Commercial property 97,997 89,215 287,279 262,418 Businessowners policies 27,605 26,371 82,157 78,624 Bonds 9,226 8,990 28,075 26,861 Other 5,266 4,841 15,477 14,326 Miscellaneous income 5,521 2,782 11,107 7,544 Total Standard Commercial Lines revenue 563,606 517,943 1,586,776 1,526,538 Standard Personal Lines: Net premiums earned: Personal automobile 42,458 43,226 123,134 129,777 Homeowners 31,395 31,529 94,537 95,672 Other 2,123 1,983 6,066 5,709 Miscellaneous income 598 380 1,520 991 Total Standard Personal Lines revenue 76,574 77,118 225,257 232,149 E&S Lines: Net premiums earned: Casualty lines 43,650 47,171 130,444 136,455 Property lines 16,830 14,550 47,065 42,205 Total E&S Lines revenue 60,480 61,721 177,509 178,660 Investments: Net investment income 68,185 55,826 158,596 164,949 Net realized and unrealized investment gains (losses) 7,721 (2,183) (24,296) 15,295 Total Investments revenue 75,906 53,643 134,300 180,244 Total revenues $ 776,566 710,425 2,123,842 2,117,591 Income Before and After Federal Income Tax Quarter ended September 30, Nine Months ended September 30, ($ in thousands) 2020 2019 2020 2019 Standard Commercial Lines: Underwriting gain, before federal income tax $ 42,718 30,016 76,574 92,974 Underwriting gain, after federal income tax 33,746 23,713 60,493 73,450 Combined ratio 92.3 % 94.2 95.1 93.9 ROE contribution 5.7 4.5 3.5 5.0 Standard Personal Lines: Underwriting (loss) gain, before federal income tax $ (14,404) (631) (20,342) 7,074 Underwriting (loss) gain, after federal income tax (11,379) (499) (16,070) 5,588 Combined ratio 119.0 % 100.8 109.1 96.9 ROE contribution (1.9) (0.1) (0.9) 0.4 E&S Lines: Underwriting (loss) gain, before federal income tax $ (7,277) 1,916 (3,965) 9,439 Underwriting (loss) gain, after federal income tax (5,748) 1,514 (3,132) 7,457 Combined ratio 112.0 % 96.9 102.2 94.7 ROE contribution (1.0) 0.3 (0.2) 0.5 Investments: Net investment income $ 68,185 55,826 158,596 164,949 Net realized and unrealized investment gains (losses) 7,721 (2,183) (24,296) 15,295 Total investment segment income, before federal income tax 75,906 53,643 134,300 180,244 Tax on investment segment income 14,676 10,884 24,338 34,733 Total investment segment income, after federal income tax $ 61,230 42,759 109,962 145,511 ROE contribution of after-tax net investment income 9.4 8.6 7.5 9.1 Reconciliation of Segment Results to Income Before Federal Income Tax Quarter ended September 30, Nine Months ended September 30, ($ in thousands) 2020 2019 2020 2019 Underwriting gain Standard Commercial Lines $ 42,718 30,016 76,574 92,974 Standard Personal Lines (14,404) (631) (20,342) 7,074 E&S Lines (7,277) 1,916 (3,965) 9,439 Investment income 75,906 53,643 134,300 180,244 Total all segments 96,943 84,944 186,567 289,731 Interest expense (7,781) (7,397) (23,310) (26,289) Corporate expenses (3,905) (6,369) (19,310) (28,345) Income, before federal income tax $ 85,257 71,178 143,947 235,097

Retirement Plans

Retirement Plans	9 Months Ended
	Sep. 30, 2020
Retirement Benefits [Abstract]
Retirement Plans	Retirement Plans The primary pension plan for our employees is the Retirement Income Plan for Selective Insurance Company of America (the “Pension Plan”). SICA also sponsors the Supplemental Excess Retirement Plan (the “Excess Plan”) and a life insurance benefit plan. All plans are closed to new entrants and benefits ceased accruing under the Pension Plan and the Excess Plan after March 31, 2016. For more information about SICA's retirement plans, see Note 14. “Retirement Plans” in Item 8. “Financial Statements and Supplementary Data.” of our 2019 Annual Report. The following tables provide information about the Pension Plan: Pension Plan Pension Plan Quarter ended September 30, Nine Months ended September 30, ($ in thousands) 2020 2019 2020 2019 Net Periodic Pension Cost (Benefit): Interest cost $ 2,828 3,376 8,484 10,129 Expected return on plan assets (5,477) (5,278) (16,430) (15,835) Amortization of unrecognized net actuarial loss 704 644 2,112 1,931 Total net periodic pension cost (benefit) 1 $ (1,945) (1,258) (5,834) (3,775) 1 The components of net periodic pension cost (benefit) are included within "Loss and loss expense incurred" and "Other insurance expenses" on the Consolidated Statements of Income. Pension Plan Nine Months ended September 30, 2020 2019 Weighted-Average Expense Assumptions: Discount rate 3.33 % 4.46 % Effective interest rate for calculation of interest cost 2.95 4.12 Expected return on plan assets 5.80 6.50

Comprehensive Income

Comprehensive Income	3 Months Ended
	Sep. 30, 2020
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Comprehensive Income	Comprehensive Income The following are the components of comprehensive income, both gross and net of tax, for Third Quarter and Nine Months 2020 and 2019 : Third Quarter 2020 ($ in thousands) Gross Tax Net Net income $ 85,257 15,382 69,875 Components of OCI: Unrealized gains on investment securities : Unrealized holding gains during the period 37,836 7,947 29,889 Non-credit portion of OTTI recognized in OCI 9,239 1,940 7,299 Amounts reclassified into net income: HTM securities (1) (1) — Realized gains on disposals and intent-to-sell OTTI on AFS securities (515) (109) (406) Credit loss benefit recognized in OTTI (2,853) (599) (2,254) Total unrealized gains on investment securities 43,706 9,178 34,528 Defined benefit pension and post-retirement plans: Amounts reclassified into net income: Net actuarial loss 754 158 596 Total defined benefit pension and post-retirement plans 754 158 596 Other comprehensive income 44,460 9,336 35,124 Comprehensive income $ 129,717 24,718 104,999 Third Quarter 2019 ($ in thousands) Gross Tax Net Net income $ 71,178 15,028 56,150 Components of OCI: Unrealized gains on investment securities : Unrealized holding gains during the period 34,392 7,224 27,168 Amounts reclassified into net income: HTM securities (3) (1) (2) Realized losses on disposals and OTTI of AFS securities 2,821 592 2,229 Total unrealized gains on investment securities 37,210 7,815 29,395 Defined benefit pension and post-retirement plans: Amounts reclassified into net income: Net actuarial loss 665 140 525 Total defined benefit pension and post-retirement plans 665 140 525 Other comprehensive income 37,875 7,955 29,920 Comprehensive income $ 109,053 22,983 86,070 Nine Months 2020 ($ in thousands) Gross Tax Net Net income $ 143,947 24,653 119,294 Components of OCI: Unrealized gains on investment securities: Unrealized holding gains during the period 132,623 27,852 104,771 Non-credit portion of OTTI recognized in OCI (18,672) (3,921) (14,751) Amounts reclassified into net income: HTM securities (7) (2) (5) Realized losses on disposals and intent-to-sell OTTI on AFS securities 9,126 1,916 7,210 Credit loss expense recognized in OTTI 8,010 1,682 6,328 Total unrealized gains on investment securities 131,080 27,527 103,553 Defined benefit pension and post-retirement plans: Amounts reclassified into net income: Net actuarial loss 2,261 474 1,787 Total defined benefit pension and post-retirement plans 2,261 474 1,787 Other comprehensive income 133,341 28,001 105,340 Comprehensive income $ 277,288 52,654 224,634 Nine Months 2019 ($ in thousands) Gross Tax Net Net income $ 235,097 45,333 189,764 Components of OCI: Unrealized gains on investment securities: Unrealized holding gains during the period 220,864 46,381 174,483 Amounts reclassified into net income: HTM securities (33) (7) (26) Realized losses on disposals and OTTI of AFS securities 444 93 351 Total unrealized gains on investment securities 221,275 46,467 174,808 Defined benefit pension and post-retirement plans: Amounts reclassified into net income: Net actuarial loss 1,993 419 1,574 Total defined benefit pension and post-retirement plans 1,993 419 1,574 Other comprehensive income 223,268 46,886 176,382 Comprehensive income $ 458,365 92,219 366,146 The following are the balances and changes in each component of AOCI (net of taxes) as of September 30, 2020: September 30, 2020 Defined Benefit Net Unrealized Gains (Losses) on Investment Securities Total AOCI ($ in thousands) OTTI Related 1 HTM All Investments Balance, December 31, 2019 $ (71) 25 170,439 170,393 (88,643) 81,750 OCI before reclassifications (14,751) — 104,771 90,020 — 90,020 Amounts reclassified from AOCI 6,328 (5) 7,210 13,533 1,787 15,320 Net current period OCI (8,423) (5) 111,981 103,553 1,787 105,340 Balance, September 30, 2020 $ (8,494) 20 282,420 273,946 (86,856) 187,090 1 Represents unrealized gains and losses on AFS securities with credit-related OTTI recognized in earnings. The reclassifications out of AOCI were as follows: Quarter ended September 30, Nine Months ended September 30, Affected Line Item in the Unaudited Consolidated Statements of Income ($ in thousands) 2020 2019 2020 2019 HTM related Unrealized losses (gains) on HTM disposals $ 4 (3) 5 (12) Net realized and unrealized gains (losses) Amortization of net unrealized gains on HTM securities (5) — (12) (21) Net investment income earned (1) (3) (7) (33) Income before federal income tax 1 1 2 7 Total federal income tax expense — (2) (5) (26) Net income Net realized (gains) losses on disposals and intent-to-sell OTTI Net realized (gains) losses on disposals and intent-to-sell OTTI (515) 2,821 9,126 444 Net realized and unrealized gains (losses) (515) 2,821 9,126 444 Income before federal income tax 109 (592) (1,916) (93) Total federal income tax expense (406) 2,229 7,210 351 Net income OTTI related Credit loss (benefit) expense recognized in OTTI (2,853) — 8,010 — Net realized and unrealized gains (losses) (2,853) — 8,010 — Income before federal income tax 599 — (1,682) — Total federal income tax expense (2,254) — 6,328 — Net income Defined benefit pension and post-retirement life plans Net actuarial loss 162 146 486 436 Loss and loss expense incurred 592 519 1,775 1,557 Other insurance expenses Total defined benefit pension and post-retirement life 754 665 2,261 1,993 Income before federal income tax (158) (140) (474) (419) Total federal income tax expense 596 525 1,787 1,574 Net income Total reclassifications for the period $ (2,064) 2,752 15,320 1,899 Net income

Litigation

Litigation	9 Months Ended
	Sep. 30, 2020
Loss Contingency, Information about Litigation Matters [Abstract]
Litigation	Litigation As of September 30, 2020, we do not believe we are involved in any legal action that could have a material adverse effect on our consolidated financial condition, results of operations, or cash flows. In the ordinary course of conducting business, we are parties in various legal actions. Most are claims litigation involving our Insurance Subsidiaries as (i) liability insurers defending or providing indemnity for third-party claims brought against our customers, (ii) insurers defending first-party coverage claims brought against them, or (iii) liability insurers seeking declaratory judgment on our insurance coverage obligations. We account for such activity through the establishment of unpaid loss and loss expense reserves. In ordinary course claims litigation, we expect that any potential ultimate liability, after consideration of provisions made for potential losses and costs of defense, will not be material to our consolidated financial condition, results of operations, or cash flows. All of our commercial property and businessowners policies require direct physical loss of or damage to property by a covered cause of loss. It also is our practice to include in, or attach to, all standard lines commercial property and businessowners policies an exclusion that states that all loss or property damage caused by or resulting from any virus, bacterium, or other microorganism that induces or is capable of inducing physical distress, illness, or disease is not a covered cause of loss ("Virus Exclusion"). Whether COVID-19-related contamination, the existence of the COVID-19 pandemic, and the resulting COVID-19-related government shutdown orders cause physical loss of or damage to property is the subject of much public debate and first-party coverage litigation against some insurers, including us. The Virus Exclusion also is the subject of first-party coverage litigation against some insurers, including us. We cannot predict the outcome of litigation over these two coverage issues, including interpretation of provisions similar or identical to those in our insurance policies. From time to time, our Insurance Subsidiaries also are named as defendants in other legal actions, some of which assert claims for substantial amounts. Plaintiffs may style these actions as putative class actions and seek judicial certification of a state or national class for allegations involving our business practices, such as improper reimbursement of medical providers paid under workers compensation and personal and commercial automobile insurance policies or improper reimbursement for automobile

Statements of Cash Flows (Table

Statements of Cash Flows (Tables)	9 Months Ended
	Sep. 30, 2020
Supplemental Cash Flow Information [Abstract]
Schedule of Cash Flow, Supplemental Disclosures	Nine Months ended September 30, ($ in thousands) 2020 2019 Cash paid during the period for: Interest $ 24,449 19,261 Federal income tax 34,000 42,000 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases 7,077 6,062 Operating cash flows from financing leases 13 12 Financing cash flows from finance leases 429 811 Non-cash items: Corporate actions related to fixed income securities, AFS 1 32,580 29,771 Corporate actions related to fixed income securities, HTM 1 2,596 — Corporate actions related to equity securities 1 890 14,250 Assets acquired under finance lease arrangements 119 824 Assets acquired under operating lease arrangements 22,104 13,648 Non-cash purchase of property and equipment 9 108 1 Examples of such corporate actions include exchanges, non-cash acquisitions, and stock splits.
Schedule of Cash and Restricted Cash	($ in thousands) September 30, 2020 December 31, 2019 Cash $ 785 300 Restricted cash 15,110 7,675 Total cash and restricted cash shown in the Statements of Cash Flows $ 15,895 7,975

Investments (Tables)

Investments (Tables)	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020
Schedule of Investments [Line Items]
Schedule of Available-for-sale Securities		September 30, 2020 ($ in thousands) Cost/ Allowance for Credit Losses Unrealized Unrealized Fair AFS fixed income securities: U.S. government and government agencies $ 110,201 — 7,374 (46) 117,529 Foreign government 15,679 (7) 1,336 — 17,008 Obligations of states and political subdivisions 1,152,794 (15) 78,841 (164) 1,231,456 Corporate securities 2,154,302 (5,358) 157,689 (7,802) 2,298,831 Collateralized loan obligations ("CLO") and other asset-backed securities ("ABS") 942,627 (1,121) 18,274 (14,198) 945,582 Residential mortgage-backed securities ("RMBS") 1,122,678 (647) 61,259 (333) 1,182,957 Commercial mortgage-backed securities ("CMBS") 599,692 (32) 46,386 (1,872) 644,174 Total AFS fixed income securities $ 6,097,973 (7,180) 371,159 (24,415) 6,437,537 December 31, 2019 ($ in thousands) Cost/ Unrealized Unrealized Fair AFS fixed income securities: U.S. government and government agencies $ 112,680 3,506 — 116,186 Foreign government 18,011 533 (2) 18,542 Obligations of states and political subdivisions 1,168,185 62,175 (270) 1,230,090 Corporate securities 1,866,881 81,906 (1,310) 1,947,477 CLO and other ABS 790,517 7,929 (5,434) 793,012 RMBS 1,409,003 43,421 (455) 1,451,969 CMBS 514,709 23,902 (267) 538,344 Total AFS fixed income securities $ 5,879,986 223,372 (7,738) 6,095,620
Debt Securities, Available-for-sale, Allowance for Credit Loss [Table Text Block]		Quarter ended September 30, 2020 ($ in thousands) Beginning Balance Current Provision for Securities without Prior Allowance Increase (Decrease) on Securities with Prior Allowance, excluding intent (or Requirement) to Sell Securities Reductions for Securities Sold Reductions for Securities Identified as Intent (or Requirement) to Sell during the Period Ending Balance Foreign government $ 28 — (2) (19) — 7 Obligations of states and political subdivisions 17 9 (11) — — 15 Corporate securities 8,077 1,016 (3,455) (265) (15) 5,358 CLO and other ABS 1,389 — (210) (51) (7) 1,121 RMBS 831 — (157) (27) — 647 CMBS 53 — (21) — — 32 Total AFS fixed income securities $ 10,395 1,025 (3,856) (362) (22) 7,180 Nine Months ended September 30, 2020 ($ in thousands) Beginning Balance Current Provision for Securities without Prior Allowance Increase (Decrease) on Securities with Prior Allowance, excluding intent (or Requirement) to Sell Securities Reductions for Securities Sold Reductions for Securities Identified as Intent (or Requirement) to Sell during the Period Ending Balance Foreign government $ — 26 — (19) — 7 Obligations of states and political subdivisions — 15 — — — 15 Corporate securities — 6,100 — (659) (83) 5,358 CLO and other ABS — 1,237 — (109) (7) 1,121 RMBS — 690 — (43) — 647 CMBS — 32 — — — 32 Total AFS fixed income securities $ — 8,100 — (830) (90) 7,180
Schedule of Fair Value and Gross Pre-Tax Net Unrealized Loss of Securities by Length of Time, AFS		September 30, 2020 Less than 12 months 12 months or longer Total ($ in thousands) Fair Value Unrealized Fair Value Unrealized Fair Value Unrealized AFS fixed income securities: U.S. government and government agencies $ 4,855 (46) — — 4,855 (46) Obligations of states and political subdivisions 15,929 (164) — — 15,929 (164) Corporate securities 100,989 (7,444) 2,695 (358) 103,684 (7,802) CLO and other ABS 302,492 (7,804) 149,893 (6,394) 452,385 (14,198) RMBS 55,128 (300) 2,316 (33) 57,444 (333) CMBS 80,308 (1,320) 14,342 (552) 94,650 (1,872) Total AFS fixed income securities $ 559,701 (17,078) 169,246 (7,337) 728,947 (24,415) December 31, 2019 Less than 12 months 12 months or longer Total ($ in thousands) Fair Unrealized Fair Value Unrealized Fair Value Unrealized AFS fixed income securities: Foreign government $ 1,416 (2) — — 1,416 (2) Obligations of states and political subdivisions 35,838 (270) — — 35,838 (270) Corporate securities 84,832 (480) 20,182 (830) 105,014 (1,310) CLO and other ABS 205,191 (1,938) 204,385 (3,496) 409,576 (5,434) RMBS 126,089 (425) 5,375 (30) 131,464 (455) CMBS 62,893 (264) 828 (3) 63,721 (267) Total AFS fixed income securities $ 516,259 (3,379) 230,770 (4,359) 747,029 (7,738)
Schedule of Fixed Maturity Securities By Contractual Maturities		AFS HTM ($ in thousands) Fair Value Carrying Value Fair Value Due in one year or less $ 336,142 1,456 1,490 Due after one year through five years 3,714,414 15,131 16,293 Due after five years through 10 years 1,960,132 2,500 2,430 Due after 10 years 426,849 — — Total fixed income securities $ 6,437,537 19,087 20,213
Schedule of Other Investment Portfolio By Strategy And Remaining Commitment Amount and Maximum Exposure to Loss Associated With Each Strategy		Other Investments September 30, 2020 December 31, 2019 ($ in thousands) Carrying Value Remaining Commitment Maximum Exposure to Loss 1 Carrying Value Remaining Commitment Maximum Exposure to Loss 1 Alternative Investments Private equity $ 146,810 110,173 256,983 118,352 93,138 211,490 Private credit 49,254 96,131 145,385 42,532 105,340 147,872 Real assets 21,859 19,070 40,929 23,256 20,741 43,997 Total alternative investments 217,923 225,374 443,297 184,140 219,219 403,359 Other securities 40,725 — 40,725 32,667 — 32,667 Total other investments $ 258,648 225,374 484,022 216,807 219,219 436,026 1 The maximum exposure to loss includes both the carry value of these investments and the related remaining commitments. In addition, tax credits that have been previously recognized in Other securities are subject to the risk of recapture, which we do not consider significant.
Schedule of Aggregated Summarized Income Statement Financial Information For Partnerships In Our Alternative Investment Portfolio		Income Statement Information Quarter ended September 30, Nine Months ended September 30, ($ in millions) 2020 2019 2020 2019 Net investment (loss) income $ 83.4 (14.0) 92.9 10.1 Realized (losses) gains 731.3 121.1 1,075.0 370.4 Net change in unrealized appreciation (depreciation) 2,230.4 1,739.4 571.6 4,517.4 Net income $ 3,045.1 1,846.5 1,739.5 4,897.9 Insurance Subsidiaries’ alternative investments income $ 18.7 5.2 8.9 13.0
Schedule of Securities Pledged As Collateral		($ in millions) FHLBI Collateral FHLBNY Collateral State and Total U.S. government and government agencies $ — — 22.7 22.7 Obligations of states and political subdivisions — — 5.1 5.1 RMBS 133.0 205.2 — 338.2 CMBS 7.2 36.7 — 43.9 Total pledged as collateral $ 140.2 241.9 27.8 409.9
Schedule of Pre-Tax Net Investment Income Earned		Quarter ended September 30, Nine Months ended September 30, ($ in thousands) 2020 2019 2020 2019 Fixed income securities $ 51,285 50,749 152,617 150,689 CMLs 245 — 463 — Equity securities 1,948 1,885 5,523 5,265 Short-term investments 244 1,410 1,830 5,213 Other investments 18,671 5,267 9,167 13,421 Investment expenses (4,208) (3,485) (11,004) (9,639) Net investment income earned $ 68,185 55,826 158,596 164,949
Schedule Of O T T I By Asset Type [Table Text Block]	Quarter ended September 30, 2020 2019 ($ in thousands) Credit Loss Other Impairment Expense Recognized in Earnings Recognized in Earnings HTM fixed income securities: Corporate securities $ 3 — 3 — Total HTM fixed income securities 3 — 3 — AFS fixed income securities: Foreign government 3 — 3 — Obligations of states and political subdivisions 2 — 2 — Corporate securities 2,454 — 2,454 (1,681) CLO and other ABS 217 (44) 173 — RMBS 157 — 157 — CMBS 21 — 21 — Total AFS fixed income securities 2,854 (44) 2,810 (1,681) CMLs (2) — (2) — Short term investments (1) — (1) — Other investments — — — (610) Total OTTI benefit (expense) $ 2,854 (44) 2,810 (2,291) Nine Months ended September 30, 2020 2019 ($ in thousands) Credit Loss (Expense) Benefit Other Impairment Expense Recognized in Earnings Recognized in Earnings HTM fixed income securities: Corporate securities $ 4 — 4 — Total HTM fixed income securities 4 — 4 — AFS fixed income securities: U.S. government and government agencies — (14) (14) — Foreign government (25) — (25) — Obligations of states and political subdivisions (15) (62) (77) (65) Corporate securities (6,018) (12,103) (18,121) (2,455) CLO and other ABS (1,230) (2,137) (3,367) — RMBS (690) (91) (781) — CMBS (32) (1,852) (1,884) — Total AFS fixed income securities (8,010) (16,259) (24,269) (2,520) CMLs (220) — (220) — Short-term investments (1) — (1) — Other investments — — — (846) Total OTTI expense $ (8,227) (16,259) (24,486) (3,366)
Schedule of Components of Net Realized and Unrealized Gains and Losses Excluding OTTI Charges		Quarter ended September 30, Nine Months ended September 30, ($ in thousands) 2020 2019 2020 2019 Net realized gains (losses) on the disposals of securities: Fixed income securities $ 561 (1,141) 7,137 2,063 CMLs 1 — 2 — Equity securities — 21,602 (3) 24,733 Short-term investments 11 (36) 157 (21) Other investments — — (5) (23) Net realized gains (losses) on the disposal of securities 573 20,425 7,288 26,752 OTTI benefit (expense) 2,810 (2,291) (24,486) (3,366) Net realized gains (losses) 3,383 18,134 (17,198) 23,386 Unrealized gains (losses) recognized in income on equity securities 4,338 (20,317) (7,098) (8,091) Total net realized and unrealized investment gains (losses) $ 7,721 (2,183) $ (24,296) 15,295
Schedule of Realized Gains and Losses on Disposals of Securities		Quarter ended September 30, Nine Months ended September 30, ($ in thousands) 2020 2019 2020 2019 HTM fixed income securities Gains $ 1 — 2 1 Losses — — — (15) AFS fixed income securities Gains 2,955 1,078 14,770 5,565 Losses (2,395) (2,219) (7,635) (3,488) CMLs Gains 1 — 2 — Losses — — — — Equity securities Gains — 21,630 — 24,868 Losses — (28) (3) (135) Short-term investments Gains 18 2 355 18 Losses (7) (38) (198) (39) Other investments Gains — — — 7 Losses — — (5) (30) Total net realized gains on disposals of securities $ 573 20,425 7,288 26,752
Equity Securities [Member]
Schedule of Investments [Line Items]
Schedule of Components of Net Realized and Unrealized Gains and Losses Excluding OTTI Charges		Quarter ended September 30, Nine Months ended September 30, ($ in thousands) 2020 2019 2020 2019 Unrealized gains (losses) recognized in income on equity securities: On securities remaining in our portfolio at September 30, 2020 $ 4,338 1,109 (7,101) 1,805 On securities sold in each respective period — (21,426) 3 (9,896) Total unrealized gains (losses) recognized in income on equity securities $ 4,338 (20,317) (7,098) (8,091)

Indebtedness (Tables)

Indebtedness (Tables)	9 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Schedule of Outstanding Debt	Outstanding Debt Issuance Date Maturity Date Interest Rate Original Amount 2020 Carry Value ($ in thousands) Unamortized Issuance Costs Debt Discount September 30, 2020 December 31, 2019 Description Short-term Issuance: FHLBNY 9/14/2020 11/16/2020 0.36 % 100,000 — — 100,000 — FHLBI 3/19/2020 12/14/2020 0.58 % 67,000 — — 67,000 — Total short-term debt — — 167,000 — Other Outstanding: FHLBI 12/16/2016 12/16/2026 3.03 % 60,000 — — 60,000 60,000 FHLBNY 8/15/2016 8/16/2021 1.56 % 25,000 — — 25,000 25,000 FHLBNY 7/21/2016 7/21/2021 1.61 % 25,000 — — 25,000 25,000 Senior Notes 11/3/2005 11/1/2035 6.70 % 100,000 329 505 99,166 99,125 Senior Notes 11/16/2004 11/15/2034 7.25 % 50,000 170 87 49,743 49,725 Senior Notes 3/1/2019 3/1/2049 5.375 % 300,000 2,986 5,781 291,233 291,010 Finance lease obligations 424 737 Total long-term debt 3,485 6,373 550,566 550,597 Total debt 3,485 6,373 717,566 550,597

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Schedule of Carrying Values and Estimated Fair Values of Financial Liabilities	September 30, 2020 December 31, 2019 ($ in thousands) Carrying Amount Fair Value Carrying Amount Fair Value Financial Liabilities Short-term debt: 0.36% Borrowings from FHLBNY $ 100,000 100,005 — — 0.58% Borrowings from FHLBI 67,000 67,050 — — Total short-term debt 167,000 167,055 — — Long-term debt: 7.25% Senior Notes 49,913 67,350 49,910 66,365 6.70% Senior Notes 99,495 130,651 99,480 123,104 5.375% Senior Notes 294,219 365,756 294,157 357,025 1.61% borrowings from FHLBNY 25,000 25,255 25,000 24,901 1.56% borrowings from FHLBNY 25,000 25,269 25,000 24,875 3.03% borrowings from FHLBI 60,000 67,972 60,000 63,002 Subtotal long-term debt 553,627 682,253 553,547 659,272 Unamortized debt issuance costs (3,485) (3,687) Finance lease obligations 424 737 Total long-term debt $ 550,566 550,597
Schedule of Quantitative Disclosures of Our Financial Assets That Were Measured At Fair Value	September 30, 2020 Fair Value Measurements Using ($ in thousands) Assets Quoted Prices in 1 Significant Other Observable Inputs (Level 2) 1 Significant Unobservable Description Measured on a recurring basis: AFS fixed income securities: U.S. government and government agencies $ 117,529 43,287 74,242 — Foreign government 17,008 — 17,008 — Obligations of states and political subdivisions 1,231,456 — 1,228,602 2,854 Corporate securities 2,298,831 — 2,261,195 37,636 CLO and other ABS 945,582 — 900,862 44,720 RMBS 1,182,957 — 1,182,957 — CMBS 644,174 — 644,174 — Total AFS fixed income securities 6,437,537 43,287 6,309,040 85,210 Equity securities: Common stock 1 150,153 103,603 — — Preferred stock 1,671 1,671 — — Total equity securities 151,824 105,274 — — Short-term investments 380,890 379,317 1,573 — Total assets measured at fair value $ 6,970,251 527,878 6,310,613 85,210 December 31, 2019 Fair Value Measurements Using ($ in thousands) Assets Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) 1 Significant Other Observable Inputs (Level 2) 1 Significant Unobservable Description Measured on a recurring basis: AFS fixed income securities: U.S. government and government agencies $ 116,186 41,083 75,103 — Foreign government 18,542 — 18,542 — Obligations of states and political subdivisions 1,230,090 — 1,230,090 — Corporate securities 1,947,477 — 1,930,426 17,051 CLO and other ABS 793,012 3,635 772,343 17,034 RMBS 1,451,969 — 1,451,969 — CMBS 538,344 — 538,344 — Total AFS fixed income securities 6,095,620 44,718 6,016,817 34,085 Equity securities: Common stock 1 69,900 32,145 — — Preferred stock 3,037 3,037 — — Total equity securities 72,937 35,182 — — Short-term investments 282,490 265,306 17,184 — Total assets measured at fair value $ 6,451,047 345,206 6,034,001 34,085
Schedule of Changes in Fair Value of Securities Using Level 3 Inputs	September 30, 2020 ($ in thousands) Obligations of states and political subdivisions Corporate Securities CLO and Other ABS Total Fair value, December 31, 2019 — 17,051 17,034 34,085 Total net (losses) gains for the period included in: OCI (36) (2,415) 732 (1,719) Net realized and unrealized (losses) gains — (456) (247) (703) Net investment income earned — — 3 3 Purchases — 19,002 11,751 30,753 Sales — — — — Issuances — — — — Settlements — (138) (1,030) (1,168) Transfers into Level 3 2,890 4,592 26,401 33,883 Transfers out of Level 3 — — (9,924) (9,924) Fair value, September 30, 2020 2,854 37,636 44,720 85,210 Change in unrealized (losses) gains for the period included in earnings for assets held at period end — (456) (247) (703) Change in unrealized gains (losses) for the period included in OCI for assets held at period end (36) (2,415) 732 (1,719) September 30, 2019 ($ in thousands) Corporate Securities CLO and Other ABS Total Fair value, December 31, 2018 — 7,409 7,409 Total net (losses) gains for the period included in: OCI (69) (14) (83) Net investment income earned — 244 244 Purchases — 18,404 18,404 Sales — — — Issuances — — — Settlements — (105) (105) Transfers into Level 3 16,419 13,603 30,022 Transfers out of Level 3 — (19,662) (19,662) Fair value, September 30, 2019 16,350 19,879 36,229 Change in unrealized gains (losses) for the period included in earnings for assets held at period end — — —
Schedule of Quantitative Information of Our Financial Assets and Liabilities That Were Disclosed at Fair Value	September 30, 2020 Fair Value Measurements Using ($ in thousands) Assets/ Quoted Prices in Significant Other Significant Financial Assets HTM: Obligations of states and political subdivisions $ 4,849 — 4,849 — Corporate securities 15,364 — 15,364 — Total HTM fixed income securities $ 20,213 — 20,213 — CMLs $ 30,595 — 2,540 28,055 Financial Liabilities Short-term debt: 0.36% Borrowings from FHLBNY $ 100,005 — 100,005 — 0.58% Borrowings from FHLBI 67,050 — 67,050 — Total short-term debt $ 167,055 — 167,055 — Long-term debt: 7.25% Senior Notes $ 67,350 — 67,350 — 6.70% Senior Notes 130,651 — 130,651 — 5.375% Senior Notes 365,756 — 365,756 — 1.61% borrowings from FHLBNY 25,255 — 25,255 — 1.56% borrowings from FHLBNY 25,269 — 25,269 — 3.03% borrowings from FHLBI 67,972 — 67,972 — Total long-term debt $ 682,253 — 682,253 — December 31, 2019 Fair Value Measurements Using ($ in thousands) Assets/ Quoted Prices in Significant Other Significant Financial Assets HTM: Obligations of states and political subdivisions $ 4,921 — 4,921 — Corporate securities 17,054 — 17,054 — Total HTM fixed income securities $ 21,975 — 21,975 — Financial Liabilities Long-term debt: 7.25% Senior Notes $ 66,365 — 66,365 — 6.70% Senior Notes 123,104 — 123,104 — 5.375% Senior Notes 357,025 — 357,025 — 1.61% borrowings from FHLBNY 24,901 — 24,901 — 1.56% borrowings from FHLBNY 24,875 — 24,875 — 3.03% borrowings from FHLBI 63,002 — 63,002 — Total long-term debt $ 659,272 — 659,272 —

Allowance for Uncollectible P_2

Allowance for Uncollectible Premiums Receivable (Tables)	9 Months Ended
	Sep. 30, 2020
Premiums Receivable [Abstract]
Premium Receivable, Allowance for Credit Loss [Table Text Block]	($ in thousands) Quarter ended September 30, 2020 Nine Months ended September 30, 2020 Balance at beginning of period $ 21,000 $ 6,400 Cumulative effect adjustment 1 — 1,058 Balance at beginning of period, as adjusted $ 21,000 $ 7,458 Current period provision for expected credit losses 802 16,369 Write-offs charged against the allowance for credit losses (996) (3,272) Recoveries 194 445 Allowance for credit losses, end of period $ 21,000 $ 21,000

Reinsurance (Tables)

Reinsurance (Tables)	9 Months Ended
	Sep. 30, 2020
Reinsurance Disclosures [Abstract]
Reinsurance Recoverable, Credit Quality Indicator [Table Text Block]	September 30, 2020 ($ in thousands) Current Past Due Total Reinsurance Recoverables Financial strength rating of rated reinsurers 1 A++ $ 23,497 $ 230 $ 23,727 A+ 251,341 3,102 254,443 A 103,560 1,569 105,129 A- 115,196 — 115,196 B++ 95 288 383 B+ 10 — 10 Total rated reinsurers $ 493,699 $ 5,189 $ 498,888 Non-rated reinsurers Federal and state pools $ 111,399 $ — $ 111,399 Other than federal and state pools 2,919 81 3,000 Total non-rated reinsurers $ 114,318 $ 81 $ 114,399 Total reinsurance recoverable, gross $ 608,017 $ 5,270 $ 613,287 Less: allowance for credit losses 2 (1,831) Total reinsurance recoverable, net $ 611,456 1 Credit ratings as of September 30, 2020.
Reinsurance Recoverable, Allowance for Credit Loss [Table Text Block]	($ in thousands) Quarter ended September 30, 2020 Nine Months ended September 30, 2020 Balance at beginning of period $ 2,396 $ 4,400 Cumulative effect adjustment 1 — (2,903) Balance at beginning of period, as adjusted $ 2,396 $ 1,497 Current period provision for expected credit losses (565) 334 Write-offs charged against the allowance for credit losses — — Recoveries — — Allowance for credit losses, end of period $ 1,831 $ 1,831 1 See Note 2. "Adoption of Accounting Pronouncements" for additional information regarding our adoption of ASU 2016-13.
Schedule of List Of Direct, Assumed, And Ceded Reinsurance Amounts	Quarter ended September 30, Nine Months ended September 30, ($ in thousands) 2020 2019 2020 2019 Premiums written: Direct $ 839,275 785,680 $ 2,420,350 2,359,441 Assumed 5,450 6,882 17,902 18,770 Ceded (125,217) (115,634) (346,665) (326,939) Net $ 719,508 676,928 $ 2,091,587 2,051,272 Premiums earned: Direct $ 803,957 752,872 $ 2,292,495 2,221,257 Assumed 6,147 6,356 18,375 18,660 Ceded (115,563) (105,608) (333,955) (311,105) Net $ 694,541 653,620 $ 1,976,915 1,928,812 Loss and loss expenses incurred: Direct $ 530,192 437,617 $ 1,407,000 1,297,975 Assumed 4,232 4,362 13,430 13,975 Ceded (86,622) (43,304) (168,355) (145,712) Net $ 447,802 398,675 $ 1,252,075 1,166,238
COVID 19 Impact [Table Text Block]	COVID-19 Impact Quarter ended September 30, 2020 Nine Months ended September 30, 2020 ($ in thousands) Premium Audit Premium Credit Total Premium Audit Property Premium Credit Total DPW $ — — — $ (75,000) — (19,740) (94,740) Direct premiums earned (16,303) — (16,303) (64,636) — (19,740) (84,376) Direct loss and loss expenses incurred (9,468) — (9,468) (37,541) 10,000 (19,740) (47,281)
Schedule of Ceded Premiums and Losses Related to Flood Operations	Ceded to NFIP Quarter ended September 30, Nine Months ended September 30, ($ in thousands) 2020 2019 2020 2019 Ceded premiums written $ (77,318) (74,863) $ (213,592) (206,451) Ceded premiums earned (68,427) (65,846) (202,656) (191,914) Ceded loss and loss expenses incurred (48,132) (27,459) (66,219) (62,208)

Reserve for Loss and Loss Exp_2

Reserve for Loss and Loss Expense (Tables)	9 Months Ended
	Sep. 30, 2020
Insurance Loss Reserves [Abstract]
Schedule of Liability for Unpaid Claims and Claims Adjustment Expense	Nine Months ended September 30, ($ in thousands) 2020 2019 Gross reserve for loss and loss expense, at beginning of year $ 4,067,163 3,893,868 Less: reinsurance recoverable on unpaid loss and loss expense, at beginning of year 1 547,066 537,388 Net reserve for loss and loss expense, at beginning of year 3,520,097 3,356,480 Incurred loss and loss expense for claims occurring in the: Current year 1,295,285 1,200,878 Prior years (43,210) (34,640) Total incurred loss and loss expense 1,252,075 1,166,238 Paid loss and loss expense for claims occurring in the: Current year 421,981 384,436 Prior years 646,974 631,589 Total paid loss and loss expense 1,068,955 1,016,025 Net reserve for loss and loss expense, at end of period 3,703,217 3,506,693 Add: Reinsurance recoverable on unpaid loss and loss expense, at end of period 590,059 548,938 Gross reserve for loss and loss expense at end of period $ 4,293,276 4,055,631 1 Includes an adjustment of $2.9 million related to our adoption of ASU 2016-13. Refer to Note 2. "Adoption of Accounting Pronouncements" for additional information.

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2020
Segment Reporting [Abstract]
Schedule of Revenue By Segment	Revenue by Segment Quarter ended September 30, Nine Months ended September 30, ($ in thousands) 2020 2019 2020 2019 Standard Commercial Lines: Net premiums earned: Commercial automobile $ 160,937 141,182 449,162 408,706 Workers compensation 75,595 75,478 204,207 232,657 General liability 181,459 169,084 509,312 495,402 Commercial property 97,997 89,215 287,279 262,418 Businessowners policies 27,605 26,371 82,157 78,624 Bonds 9,226 8,990 28,075 26,861 Other 5,266 4,841 15,477 14,326 Miscellaneous income 5,521 2,782 11,107 7,544 Total Standard Commercial Lines revenue 563,606 517,943 1,586,776 1,526,538 Standard Personal Lines: Net premiums earned: Personal automobile 42,458 43,226 123,134 129,777 Homeowners 31,395 31,529 94,537 95,672 Other 2,123 1,983 6,066 5,709 Miscellaneous income 598 380 1,520 991 Total Standard Personal Lines revenue 76,574 77,118 225,257 232,149 E&S Lines: Net premiums earned: Casualty lines 43,650 47,171 130,444 136,455 Property lines 16,830 14,550 47,065 42,205 Total E&S Lines revenue 60,480 61,721 177,509 178,660 Investments: Net investment income 68,185 55,826 158,596 164,949 Net realized and unrealized investment gains (losses) 7,721 (2,183) (24,296) 15,295 Total Investments revenue 75,906 53,643 134,300 180,244 Total revenues $ 776,566 710,425 2,123,842 2,117,591
Schedule of Income Before and After Federal Income Tax	Income Before and After Federal Income Tax Quarter ended September 30, Nine Months ended September 30, ($ in thousands) 2020 2019 2020 2019 Standard Commercial Lines: Underwriting gain, before federal income tax $ 42,718 30,016 76,574 92,974 Underwriting gain, after federal income tax 33,746 23,713 60,493 73,450 Combined ratio 92.3 % 94.2 95.1 93.9 ROE contribution 5.7 4.5 3.5 5.0 Standard Personal Lines: Underwriting (loss) gain, before federal income tax $ (14,404) (631) (20,342) 7,074 Underwriting (loss) gain, after federal income tax (11,379) (499) (16,070) 5,588 Combined ratio 119.0 % 100.8 109.1 96.9 ROE contribution (1.9) (0.1) (0.9) 0.4 E&S Lines: Underwriting (loss) gain, before federal income tax $ (7,277) 1,916 (3,965) 9,439 Underwriting (loss) gain, after federal income tax (5,748) 1,514 (3,132) 7,457 Combined ratio 112.0 % 96.9 102.2 94.7 ROE contribution (1.0) 0.3 (0.2) 0.5 Investments: Net investment income $ 68,185 55,826 158,596 164,949 Net realized and unrealized investment gains (losses) 7,721 (2,183) (24,296) 15,295 Total investment segment income, before federal income tax 75,906 53,643 134,300 180,244 Tax on investment segment income 14,676 10,884 24,338 34,733 Total investment segment income, after federal income tax $ 61,230 42,759 109,962 145,511 ROE contribution of after-tax net investment income 9.4 8.6 7.5 9.1
Schedule of Reconciliation of Segment Results to Income Before Federal Income Tax	Reconciliation of Segment Results to Income Before Federal Income Tax Quarter ended September 30, Nine Months ended September 30, ($ in thousands) 2020 2019 2020 2019 Underwriting gain Standard Commercial Lines $ 42,718 30,016 76,574 92,974 Standard Personal Lines (14,404) (631) (20,342) 7,074 E&S Lines (7,277) 1,916 (3,965) 9,439 Investment income 75,906 53,643 134,300 180,244 Total all segments 96,943 84,944 186,567 289,731 Interest expense (7,781) (7,397) (23,310) (26,289) Corporate expenses (3,905) (6,369) (19,310) (28,345) Income, before federal income tax $ 85,257 71,178 143,947 235,097

Retirement Plans (Table)

Retirement Plans (Table)	9 Months Ended
	Sep. 30, 2020
Retirement Benefits [Abstract]
Schedule of Components of Net Periodic Benefit Cost	Pension Plan Pension Plan Quarter ended September 30, Nine Months ended September 30, ($ in thousands) 2020 2019 2020 2019 Net Periodic Pension Cost (Benefit): Interest cost $ 2,828 3,376 8,484 10,129 Expected return on plan assets (5,477) (5,278) (16,430) (15,835) Amortization of unrecognized net actuarial loss 704 644 2,112 1,931 Total net periodic pension cost (benefit) 1 $ (1,945) (1,258) (5,834) (3,775) 1 The components of net periodic pension cost (benefit) are included within "Loss and loss expense incurred" and "Other insurance expenses" on the Consolidated Statements of Income.
Schedule of Weighted-Average Expense Assumptions	Pension Plan Nine Months ended September 30, 2020 2019 Weighted-Average Expense Assumptions: Discount rate 3.33 % 4.46 % Effective interest rate for calculation of interest cost 2.95 4.12 Expected return on plan assets 5.80 6.50

Comprehensive Income (Tables)

Comprehensive Income (Tables)	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Schedule of Components of Comprehensive Income-Gross and Net of Tax	Third Quarter 2020 ($ in thousands) Gross Tax Net Net income $ 85,257 15,382 69,875 Components of OCI: Unrealized gains on investment securities : Unrealized holding gains during the period 37,836 7,947 29,889 Non-credit portion of OTTI recognized in OCI 9,239 1,940 7,299 Amounts reclassified into net income: HTM securities (1) (1) — Realized gains on disposals and intent-to-sell OTTI on AFS securities (515) (109) (406) Credit loss benefit recognized in OTTI (2,853) (599) (2,254) Total unrealized gains on investment securities 43,706 9,178 34,528 Defined benefit pension and post-retirement plans: Amounts reclassified into net income: Net actuarial loss 754 158 596 Total defined benefit pension and post-retirement plans 754 158 596 Other comprehensive income 44,460 9,336 35,124 Comprehensive income $ 129,717 24,718 104,999 Third Quarter 2019 ($ in thousands) Gross Tax Net Net income $ 71,178 15,028 56,150 Components of OCI: Unrealized gains on investment securities : Unrealized holding gains during the period 34,392 7,224 27,168 Amounts reclassified into net income: HTM securities (3) (1) (2) Realized losses on disposals and OTTI of AFS securities 2,821 592 2,229 Total unrealized gains on investment securities 37,210 7,815 29,395 Defined benefit pension and post-retirement plans: Amounts reclassified into net income: Net actuarial loss 665 140 525 Total defined benefit pension and post-retirement plans 665 140 525 Other comprehensive income 37,875 7,955 29,920 Comprehensive income $ 109,053 22,983 86,070 Nine Months 2020 ($ in thousands) Gross Tax Net Net income $ 143,947 24,653 119,294 Components of OCI: Unrealized gains on investment securities: Unrealized holding gains during the period 132,623 27,852 104,771 Non-credit portion of OTTI recognized in OCI (18,672) (3,921) (14,751) Amounts reclassified into net income: HTM securities (7) (2) (5) Realized losses on disposals and intent-to-sell OTTI on AFS securities 9,126 1,916 7,210 Credit loss expense recognized in OTTI 8,010 1,682 6,328 Total unrealized gains on investment securities 131,080 27,527 103,553 Defined benefit pension and post-retirement plans: Amounts reclassified into net income: Net actuarial loss 2,261 474 1,787 Total defined benefit pension and post-retirement plans 2,261 474 1,787 Other comprehensive income 133,341 28,001 105,340 Comprehensive income $ 277,288 52,654 224,634 Nine Months 2019 ($ in thousands) Gross Tax Net Net income $ 235,097 45,333 189,764 Components of OCI: Unrealized gains on investment securities: Unrealized holding gains during the period 220,864 46,381 174,483 Amounts reclassified into net income: HTM securities (33) (7) (26) Realized losses on disposals and OTTI of AFS securities 444 93 351 Total unrealized gains on investment securities 221,275 46,467 174,808 Defined benefit pension and post-retirement plans: Amounts reclassified into net income: Net actuarial loss 1,993 419 1,574 Total defined benefit pension and post-retirement plans 1,993 419 1,574 Other comprehensive income 223,268 46,886 176,382 Comprehensive income $ 458,365 92,219 366,146	Third Quarter 2020 ($ in thousands) Gross Tax Net Net income $ 85,257 15,382 69,875 Components of OCI: Unrealized gains on investment securities : Unrealized holding gains during the period 37,836 7,947 29,889 Non-credit portion of OTTI recognized in OCI 9,239 1,940 7,299 Amounts reclassified into net income: HTM securities (1) (1) — Realized gains on disposals and intent-to-sell OTTI on AFS securities (515) (109) (406) Credit loss benefit recognized in OTTI (2,853) (599) (2,254) Total unrealized gains on investment securities 43,706 9,178 34,528 Defined benefit pension and post-retirement plans: Amounts reclassified into net income: Net actuarial loss 754 158 596 Total defined benefit pension and post-retirement plans 754 158 596 Other comprehensive income 44,460 9,336 35,124 Comprehensive income $ 129,717 24,718 104,999 Third Quarter 2019 ($ in thousands) Gross Tax Net Net income $ 71,178 15,028 56,150 Components of OCI: Unrealized gains on investment securities : Unrealized holding gains during the period 34,392 7,224 27,168 Amounts reclassified into net income: HTM securities (3) (1) (2) Realized losses on disposals and OTTI of AFS securities 2,821 592 2,229 Total unrealized gains on investment securities 37,210 7,815 29,395 Defined benefit pension and post-retirement plans: Amounts reclassified into net income: Net actuarial loss 665 140 525 Total defined benefit pension and post-retirement plans 665 140 525 Other comprehensive income 37,875 7,955 29,920 Comprehensive income $ 109,053 22,983 86,070 Nine Months 2020 ($ in thousands) Gross Tax Net Net income $ 143,947 24,653 119,294 Components of OCI: Unrealized gains on investment securities: Unrealized holding gains during the period 132,623 27,852 104,771 Non-credit portion of OTTI recognized in OCI (18,672) (3,921) (14,751) Amounts reclassified into net income: HTM securities (7) (2) (5) Realized losses on disposals and intent-to-sell OTTI on AFS securities 9,126 1,916 7,210 Credit loss expense recognized in OTTI 8,010 1,682 6,328 Total unrealized gains on investment securities 131,080 27,527 103,553 Defined benefit pension and post-retirement plans: Amounts reclassified into net income: Net actuarial loss 2,261 474 1,787 Total defined benefit pension and post-retirement plans 2,261 474 1,787 Other comprehensive income 133,341 28,001 105,340 Comprehensive income $ 277,288 52,654 224,634 Nine Months 2019 ($ in thousands) Gross Tax Net Net income $ 235,097 45,333 189,764 Components of OCI: Unrealized gains on investment securities: Unrealized holding gains during the period 220,864 46,381 174,483 Amounts reclassified into net income: HTM securities (33) (7) (26) Realized losses on disposals and OTTI of AFS securities 444 93 351 Total unrealized gains on investment securities 221,275 46,467 174,808 Defined benefit pension and post-retirement plans: Amounts reclassified into net income: Net actuarial loss 1,993 419 1,574 Total defined benefit pension and post-retirement plans 1,993 419 1,574 Other comprehensive income 223,268 46,886 176,382 Comprehensive income $ 458,365 92,219 366,146
Schedule of Components of Accumulated Other Comprehensive Income Net of Tax		September 30, 2020 Defined Benefit Net Unrealized Gains (Losses) on Investment Securities Total AOCI ($ in thousands) OTTI Related 1 HTM All Investments Balance, December 31, 2019 $ (71) 25 170,439 170,393 (88,643) 81,750 OCI before reclassifications (14,751) — 104,771 90,020 — 90,020 Amounts reclassified from AOCI 6,328 (5) 7,210 13,533 1,787 15,320 Net current period OCI (8,423) (5) 111,981 103,553 1,787 105,340 Balance, September 30, 2020 $ (8,494) 20 282,420 273,946 (86,856) 187,090
Schedule of Reclassifications Out Of Accumulated Other Comprehensive Income		Quarter ended September 30, Nine Months ended September 30, Affected Line Item in the Unaudited Consolidated Statements of Income ($ in thousands) 2020 2019 2020 2019 HTM related Unrealized losses (gains) on HTM disposals $ 4 (3) 5 (12) Net realized and unrealized gains (losses) Amortization of net unrealized gains on HTM securities (5) — (12) (21) Net investment income earned (1) (3) (7) (33) Income before federal income tax 1 1 2 7 Total federal income tax expense — (2) (5) (26) Net income Net realized (gains) losses on disposals and intent-to-sell OTTI Net realized (gains) losses on disposals and intent-to-sell OTTI (515) 2,821 9,126 444 Net realized and unrealized gains (losses) (515) 2,821 9,126 444 Income before federal income tax 109 (592) (1,916) (93) Total federal income tax expense (406) 2,229 7,210 351 Net income OTTI related Credit loss (benefit) expense recognized in OTTI (2,853) — 8,010 — Net realized and unrealized gains (losses) (2,853) — 8,010 — Income before federal income tax 599 — (1,682) — Total federal income tax expense (2,254) — 6,328 — Net income Defined benefit pension and post-retirement life plans Net actuarial loss 162 146 486 436 Loss and loss expense incurred 592 519 1,775 1,557 Other insurance expenses Total defined benefit pension and post-retirement life 754 665 2,261 1,993 Income before federal income tax (158) (140) (474) (419) Total federal income tax expense 596 525 1,787 1,574 Net income Total reclassifications for the period $ (2,064) 2,752 15,320 1,899 Net income

Statements of Cash Flows (Cash

Statements of Cash Flows (Cash Flow Supplemental Disclosures) (Details) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019
Federal income tax		$ 34,000	$ 42,000
Operating cash flows from operating leases		7,077	6,062
Operating cash flows from financing leases		13	12
Financing cash flows from finance leases		429	811
Assets acquired under finance lease arrangements		119	824
Assets acquired under operating lease arrangements		22,104	13,648
Non-cash purchase of property and equipment		9	108
Interest Paid, Operating and Investing Activities		24,449	19,261
Available-for-sale Securities
Corporate actions related to securities	[1]	32,580	29,771
Equity Securities [Member]
Corporate actions related to securities	[1]	890	14,250
Held-to-maturity Securities [Member]
Corporate actions related to securities	[1]	$ 2,596	$ 0
[1]	Examples of such corporate actions include exchanges, non-cash acquisitions, and stock splits.

Statements of Cash Flows (Sched

Statements of Cash Flows (Schedule of Cash and Restricted Cash) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Schedule of Cash and Restricted Cash [Line Items]
Cash	$ 785	$ 300
Restricted cash	15,110	7,675
Total cash and restricted cash shown in the Statements of Cash Flows	$ 15,895	$ 7,975	$ 10,163	$ 16,919

Investments (Available-For-Sale

Investments (Available-For-Sale Securities Disclosure) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Cost/Amortized Cost	$ 6,097,973	$ 6,097,973	$ 5,879,986
Allowance for credit losses, Period beginning balance	10,395	0
Allowance for credit losses, ending balance at September 30, 2020	7,180	7,180
Interest and dividends due or accrued	46,392	46,392	44,846
Current provision for securities without prior allowance	1,025	8,100
Increase or (Decrease) on securities with prior allowance, excluding intent (or Requirements) to sell securities	(3,856)	0
Reductions for securities sold	(362)	(830)
Reductions for securities identified as intent (or requirement) to sell during the period	(22)	(90)
Unrealized Gains	371,159	371,159	223,372
Unrealized Losses	(24,415)	(24,415)	(7,738)
Debt Securities, Available-for-sale, Fair Value	6,437,537	6,437,537	6,095,620
Available-for-sale Securities [Member]
Debt Securities, Available-for-sale [Line Items]
AFS Unrealized Losses	24,400	24,400	7,700
Available-for-sale Securities | U.S. Government and Government Agencies [Member]
Debt Securities, Available-for-sale [Line Items]
Cost/Amortized Cost	110,201	110,201	112,680
Allowance for credit losses, ending balance at September 30, 2020	0	0
Unrealized Gains	7,374	7,374	3,506
Unrealized Losses	(46)	(46)	0
Debt Securities, Available-for-sale, Fair Value	117,529	117,529	116,186
Available-for-sale Securities | Foreign Government [Member]
Debt Securities, Available-for-sale [Line Items]
Cost/Amortized Cost	15,679	15,679	18,011
Allowance for credit losses, Period beginning balance	28	0
Allowance for credit losses, ending balance at September 30, 2020	7	7
Current provision for securities without prior allowance	0	26
Increase or (Decrease) on securities with prior allowance, excluding intent (or Requirements) to sell securities	(2)	0
Reductions for securities sold	(19)	(19)
Reductions for securities identified as intent (or requirement) to sell during the period	0	0
Unrealized Gains	1,336	1,336	533
Unrealized Losses	0	0	(2)
Debt Securities, Available-for-sale, Fair Value	17,008	17,008	18,542
Available-for-sale Securities | Obligations of States and Political Subdivisions [Member]
Debt Securities, Available-for-sale [Line Items]
Cost/Amortized Cost	1,152,794	1,152,794	1,168,185
Allowance for credit losses, Period beginning balance	17	0
Allowance for credit losses, ending balance at September 30, 2020	15	15
Current provision for securities without prior allowance	9	15
Increase or (Decrease) on securities with prior allowance, excluding intent (or Requirements) to sell securities	(11)	0
Reductions for securities sold	0	0
Reductions for securities identified as intent (or requirement) to sell during the period	0	0
Unrealized Gains	78,841	78,841	62,175
Unrealized Losses	(164)	(164)	(270)
Debt Securities, Available-for-sale, Fair Value	1,231,456	1,231,456	1,230,090
Available-for-sale Securities | Corporate Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost/Amortized Cost	2,154,302	2,154,302	1,866,881
Allowance for credit losses, Period beginning balance	8,077	0
Allowance for credit losses, ending balance at September 30, 2020	5,358	5,358
Current provision for securities without prior allowance	1,016	6,100
Increase or (Decrease) on securities with prior allowance, excluding intent (or Requirements) to sell securities	(3,455)	0
Reductions for securities sold	(265)	(659)
Reductions for securities identified as intent (or requirement) to sell during the period	(15)	(83)
Unrealized Gains	157,689	157,689	81,906
Unrealized Losses	(7,802)	(7,802)	(1,310)
Debt Securities, Available-for-sale, Fair Value	2,298,831	2,298,831	1,947,477
Available-for-sale Securities | Collateralized Loan Obligations and Other Asset Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost/Amortized Cost	942,627	942,627	790,517
Allowance for credit losses, Period beginning balance	1,389	0
Allowance for credit losses, ending balance at September 30, 2020	1,121	1,121
Current provision for securities without prior allowance	0	1,237
Increase or (Decrease) on securities with prior allowance, excluding intent (or Requirements) to sell securities	(210)	0
Reductions for securities sold	(51)	(109)
Reductions for securities identified as intent (or requirement) to sell during the period	(7)	(7)
Unrealized Gains	18,274	18,274	7,929
Unrealized Losses	(14,198)	(14,198)	(5,434)
Debt Securities, Available-for-sale, Fair Value	945,582	945,582	793,012
Available-for-sale Securities | Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost/Amortized Cost	1,122,678	1,122,678	1,409,003
Allowance for credit losses, Period beginning balance	831	0
Allowance for credit losses, ending balance at September 30, 2020	647	647
Current provision for securities without prior allowance	0	690
Increase or (Decrease) on securities with prior allowance, excluding intent (or Requirements) to sell securities	(157)	0
Reductions for securities sold	(27)	(43)
Reductions for securities identified as intent (or requirement) to sell during the period	0	0
Unrealized Gains	61,259	61,259	43,421
Unrealized Losses	(333)	(333)	(455)
Debt Securities, Available-for-sale, Fair Value	1,182,957	1,182,957	1,451,969
Available-for-sale Securities | Commercial Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost/Amortized Cost	599,692	599,692	514,709
Allowance for credit losses, Period beginning balance	53	0
Allowance for credit losses, ending balance at September 30, 2020	32	32
Current provision for securities without prior allowance	0	32
Increase or (Decrease) on securities with prior allowance, excluding intent (or Requirements) to sell securities	(21)	0
Reductions for securities sold	0	0
Reductions for securities identified as intent (or requirement) to sell during the period	0	0
Unrealized Gains	46,386	46,386	23,902
Unrealized Losses	(1,872)	(1,872)	(267)
Debt Securities, Available-for-sale, Fair Value	644,174	644,174	$ 538,344
Available-for-sale Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Interest and dividends due or accrued	45,300	45,300
Current provision for securities without prior allowance	2,854	(8,010)
Available-for-sale Securities [Member] | U.S. Government and Government Agencies [Member]
Debt Securities, Available-for-sale [Line Items]
Current provision for securities without prior allowance		0
Available-for-sale Securities [Member] | Foreign Government [Member]
Debt Securities, Available-for-sale [Line Items]
Current provision for securities without prior allowance	3	(25)
Available-for-sale Securities [Member] | Obligations of States and Political Subdivisions [Member]
Debt Securities, Available-for-sale [Line Items]
Current provision for securities without prior allowance	2	(15)
Available-for-sale Securities [Member] | Corporate Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Current provision for securities without prior allowance	2,454	(6,018)
Available-for-sale Securities [Member] | Collateralized Loan Obligations and Other Asset Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Current provision for securities without prior allowance	217	(1,230)
Available-for-sale Securities [Member] | Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Current provision for securities without prior allowance	157	(690)
Available-for-sale Securities [Member] | Commercial Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Current provision for securities without prior allowance	$ 21	$ (32)

Investments (Fair Value and Gro

Investments (Fair Value and Gross Pre-Tax Net Unrealized Loss of Securities By Length of Time) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Available-for-sale Securities
AFS Fair Value, Less than 12 Months	$ 559,701	$ 516,259
AFS Unrealized Losses, Less than 12 months	(17,078)	(3,379)
AFS Fair Value, 12 months or longer	169,246	230,770
AFS Unrealized Losses, 12 months or longer	(7,337)	(4,359)
AFS Fair Value	728,947	747,029
AFS Unrealized Losses	(24,415)	(7,738)
Available-for-sale Securities | U.S. Government and Government Agencies [Member]
AFS Fair Value, Less than 12 Months	4,855
AFS Unrealized Losses, Less than 12 months	(46)
AFS Fair Value, 12 months or longer	0
AFS Unrealized Losses, 12 months or longer	0
AFS Fair Value	4,855
AFS Unrealized Losses	(46)
Available-for-sale Securities | Foreign Government [Member]
AFS Fair Value, Less than 12 Months		1,416
AFS Unrealized Losses, Less than 12 months		(2)
AFS Fair Value, 12 months or longer		0
AFS Unrealized Losses, 12 months or longer		0
AFS Fair Value		1,416
AFS Unrealized Losses		(2)
Available-for-sale Securities | Obligations of States and Political Subdivisions [Member]
AFS Fair Value, Less than 12 Months	15,929	35,838
AFS Unrealized Losses, Less than 12 months	(164)	(270)
AFS Fair Value, 12 months or longer	0	0
AFS Unrealized Losses, 12 months or longer	0	0
AFS Fair Value	15,929	35,838
AFS Unrealized Losses	(164)	(270)
Available-for-sale Securities | Corporate Securities [Member]
AFS Fair Value, Less than 12 Months	100,989	84,832
AFS Unrealized Losses, Less than 12 months	(7,444)	(480)
AFS Fair Value, 12 months or longer	2,695	20,182
AFS Unrealized Losses, 12 months or longer	(358)	(830)
AFS Fair Value	103,684	105,014
AFS Unrealized Losses	(7,802)	(1,310)
Available-for-sale Securities | Collateralized Loan Obligations and Other Asset Backed Securities [Member]
AFS Fair Value, Less than 12 Months	302,492	205,191
AFS Unrealized Losses, Less than 12 months	(7,804)	(1,938)
AFS Fair Value, 12 months or longer	149,893	204,385
AFS Unrealized Losses, 12 months or longer	(6,394)	(3,496)
AFS Fair Value	452,385	409,576
AFS Unrealized Losses	(14,198)	(5,434)
Available-for-sale Securities | Residential Mortgage Backed Securities [Member]
AFS Fair Value, Less than 12 Months	55,128	126,089
AFS Unrealized Losses, Less than 12 months	(300)	(425)
AFS Fair Value, 12 months or longer	2,316	5,375
AFS Unrealized Losses, 12 months or longer	(33)	(30)
AFS Fair Value	57,444	131,464
AFS Unrealized Losses	(333)	(455)
Available-for-sale Securities | Commercial Mortgage Backed Securities [Member]
AFS Fair Value, Less than 12 Months	80,308	62,893
AFS Unrealized Losses, Less than 12 months	(1,320)	(264)
AFS Fair Value, 12 months or longer	14,342	828
AFS Unrealized Losses, 12 months or longer	(552)	(3)
AFS Fair Value	94,650	63,721
AFS Unrealized Losses	(1,872)	(267)
Available-for-sale Securities [Member]
AFS Unrealized Losses	$ (24,400)	$ (7,700)

Investments (Fixed Income Secur

Investments (Fixed Income Securities by Contractual Maturity) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Schedule of Fixed Income Securities [Line Items]
Due in one year or less fair value, AFS	$ 336,142
Due after one year through five years fair value, AFS	3,714,414
Due after five years through 10 years fair value, AFS	1,960,132
Due after 10 years fair value, AFS	426,849
AFS, Fair Value	6,437,537	$ 6,095,620
Due in one year or less carrying value, HTM	1,456
Due after one year through five years carrying value, HTM	15,131
Due after five years through 10 years carrying value, HTM	2,500
Due after 10 years carrying value, HTM	0
HTM, Carrying Value	19,087	20,800
Due in one year or less fair value, HTM	1,490
Due after one year through five years fair value, HTM	16,293
Due after five years through 10 years fair value, HTM	2,430
Due after 10 years fair value, HTM	0
HTM, Fair Value	$ 20,213	$ 21,975

Investments (Other Investment P

Investments (Other Investment Portfolio by Strategy and the Remaining Commitment Amount and Maximum Exposure to Loss Associated With Each Strategy) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Net investment income earned		$ 68,185	$ 55,826	$ 158,596	$ 164,949
Carrying Value		258,648		258,648		$ 216,807
Alternative Investments [Member]
Net investment income earned		18,700	$ 5,200	8,900	$ 13,000
Other Securities [Member]
Carrying Value		40,725		40,725		32,667
Remaining Commitment		0		0		0
Maximum Exposure to Loss	[1]	40,725		40,725		32,667
Alternative Investments [Member]
Carrying Value		217,923		217,923		184,140
Remaining Commitment		225,374		225,374		219,219
Maximum Exposure to Loss	[1]	443,297		443,297		403,359
Alternative Investments [Member] | Private Equity Funds [Member]
Carrying Value		146,810		146,810		118,352
Remaining Commitment		110,173		110,173		93,138
Maximum Exposure to Loss	[1]	256,983		256,983		211,490
Alternative Investments [Member] | Private Credit Funds [Member]
Carrying Value		49,254		49,254		42,532
Remaining Commitment		96,131		96,131		105,340
Maximum Exposure to Loss	[1]	145,385		145,385		147,872
Alternative Investments [Member] | Real Assets [Member]
Carrying Value		21,859		21,859		23,256
Remaining Commitment		19,070		19,070		20,741
Maximum Exposure to Loss	[1]	40,929		40,929		43,997
Other Investments [Member]
Carrying Value		258,648		258,648		216,807
Remaining Commitment		225,374		225,374		219,219
Maximum Exposure to Loss	[1]	$ 484,022		$ 484,022		$ 436,026
[1]	The maximum exposure to loss includes both the carry value of these investments and the related remaining commitments. In addition, tax credits that have been previously recognized in Other securities are subject to the risk of recapture, which we do not consider significant.

Investments (Aggregated Income

Investments (Aggregated Income Statement Summarized Financial Information for Partnerhips in our Alternative Investment Portfolio) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Net investment income earned	$ 68,185	$ 55,826	$ 158,596	$ 164,949
Carrying Value	258,648		258,648		$ 216,807
Alternative Investments [Member]
Schedule of Equity Method Investments [Line Items]
Net investment income earned	18,700	5,200	8,900	13,000
Investments accounted for under the equity method [Member]
Schedule of Equity Method Investments [Line Items]
Net investment (loss) income	83,400	(14,000)	92,900	10,100
Realized (losses) gains	731,300	121,100	1,075,000	370,400
Net change in unrealized appreciation (depreciation)	2,230,400	1,739,400	571,600	4,517,400
Equity Method Investment, Summarized Financial Information, Net Income (Loss)	$ 3,045,100	$ 1,846,500	$ 1,739,500	$ 4,897,900

Investments (Investments Pledge

Investments (Investments Pledged as Collateral) (Details) $ in Millions	Sep. 30, 2020USD ($)
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities Pledged as Collateral On Deposit With Various State And Regulatory Agencies	$ 27.8
Securities Pledged As Collateral	409.9
Federal Home Loan Bank of Indianapolis [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities Pledged as Collateral on FHLB	140.2
Federal Home Loan Bank of New York [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities Pledged as Collateral on FHLB	241.9
U.S. Government and Government Agencies [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities Pledged as Collateral On Deposit With Various State And Regulatory Agencies	22.7
Securities Pledged As Collateral	22.7
U.S. Government and Government Agencies [Member] | Federal Home Loan Bank of Indianapolis [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities Pledged as Collateral on FHLB	0
U.S. Government and Government Agencies [Member] | Federal Home Loan Bank of New York [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities Pledged as Collateral on FHLB	0
Obligations of States and Political Subdivisions [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities Pledged as Collateral On Deposit With Various State And Regulatory Agencies	5.1
Securities Pledged As Collateral	5.1
Obligations of States and Political Subdivisions [Member] | Federal Home Loan Bank of Indianapolis [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities Pledged as Collateral on FHLB	0
Obligations of States and Political Subdivisions [Member] | Federal Home Loan Bank of New York [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities Pledged as Collateral on FHLB	0
Residential Mortgage Backed Securities [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities Pledged as Collateral On Deposit With Various State And Regulatory Agencies	0
Securities Pledged As Collateral	338.2
Residential Mortgage Backed Securities [Member] | Federal Home Loan Bank of Indianapolis [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities Pledged as Collateral on FHLB	133
Residential Mortgage Backed Securities [Member] | Federal Home Loan Bank of New York [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities Pledged as Collateral on FHLB	205.2
Commercial Mortgage Backed Securities [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities Pledged as Collateral On Deposit With Various State And Regulatory Agencies	0
Securities Pledged As Collateral	43.9
Commercial Mortgage Backed Securities [Member] | Federal Home Loan Bank of Indianapolis [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities Pledged as Collateral on FHLB	7.2
Commercial Mortgage Backed Securities [Member] | Federal Home Loan Bank of New York [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Securities Pledged as Collateral on FHLB	$ 36.7

Investments (Credit Concentrati

Investments (Credit Concentration Risk) (Details)	Sep. 30, 2020	Dec. 31, 2019
Investments [Abstract]
Maximum exposure to credit concentration risk of the Company's stockholder's equity other than certain U.S. government-backed investments	10.00%	10.00%

Investments (Net Investment Inc

Investments (Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Net Investment Income [Line Items]
Net investment income earned	$ 68,185	$ 55,826	$ 158,596	$ 164,949
Fixed Income Securities [Member]
Net Investment Income [Line Items]
Net investment income earned	51,285	50,749	152,617	150,689
Commercial Mortgage Loans [Member]
Net Investment Income [Line Items]
Net investment income earned	245	0	463	0
Equity Securities [Member]
Net Investment Income [Line Items]
Net investment income earned	1,948	1,885	5,523	5,265
Short-Term Investments [Member]
Net Investment Income [Line Items]
Net investment income earned	244	1,410	1,830	5,213
Other Investments [Member]
Net Investment Income [Line Items]
Net investment income earned	18,671	5,267	9,167	13,421
Investment Expenses [Member]
Net Investment Income [Line Items]
Net investment income earned	(4,208)	(3,485)	(11,004)	(9,639)
Alternative Investments [Member]
Net Investment Income [Line Items]
Net investment income earned	$ 18,700	$ 5,200	$ 8,900	$ 13,000

Investments (OTTI) (Details)

Investments (OTTI) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Current Provision for Securities without Prior Allowance	$ 1,025		$ 8,100
Credit Loss, (Expense) Benefit	2,854		(8,227)
Other Impairment Expense	(44)		(16,259)
OTTI benefit (expense) recognized in earnings	2,810	$ (2,291)	(24,486)	$ (3,366)
Other Investments [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Other Impairment Expense	0		0
OTTI benefit (expense) recognized in earnings	0	(610)	0	(846)
Other investments, Credit Loss (Expense) Benefit	0		0
Short-Term Investments [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Other Impairment Expense	0		0
OTTI benefit (expense) recognized in earnings	(1)	0	(1)	0
Short term investments, allowance for credit loss	(1)		(1)
Commercial Mortgage Loans [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Other Impairment Expense	0		0
OTTI benefit (expense) recognized in earnings	(2)	0	(220)	0
CML, Credit Loss (Expense) Benefit	(2)		(220)
Available-for-sale Securities [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Current Provision for Securities without Prior Allowance	2,854		(8,010)
Other Impairment Expense	(44)		(16,259)
OTTI benefit (expense) recognized in earnings	2,810	(1,681)	(24,269)	(2,520)
Available-for-sale Securities [Member] | U.S. Government and Government Agencies [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Current Provision for Securities without Prior Allowance			0
Other Impairment Expense			(14)
OTTI benefit (expense) recognized in earnings			(14)	0
Available-for-sale Securities [Member] | Foreign Government [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Current Provision for Securities without Prior Allowance	3		(25)
Other Impairment Expense	0		0
OTTI benefit (expense) recognized in earnings	3	0	(25)	0
Available-for-sale Securities [Member] | Obligations of States and Political Subdivisions [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Current Provision for Securities without Prior Allowance	2		(15)
Other Impairment Expense	0		(62)
OTTI benefit (expense) recognized in earnings	2	0	(77)	(65)
Available-for-sale Securities [Member] | Corporate Securities [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Current Provision for Securities without Prior Allowance	2,454		(6,018)
Other Impairment Expense	0		(12,103)
OTTI benefit (expense) recognized in earnings	2,454	(1,681)	(18,121)	(2,455)
Available-for-sale Securities [Member] | Collateralized Loan Obligations and Other Asset Backed Securities [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Current Provision for Securities without Prior Allowance	217		(1,230)
Other Impairment Expense	(44)		(2,137)
OTTI benefit (expense) recognized in earnings	173	0	(3,367)	0
Available-for-sale Securities [Member] | Residential Mortgage Backed Securities [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Current Provision for Securities without Prior Allowance	157		(690)
Other Impairment Expense	0		(91)
OTTI benefit (expense) recognized in earnings	157	0	(781)	0
Available-for-sale Securities [Member] | Commercial Mortgage Backed Securities [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Current Provision for Securities without Prior Allowance	21		(32)
Other Impairment Expense	0		(1,852)
OTTI benefit (expense) recognized in earnings	21	0	(1,884)	0
Held-to-maturity Securities [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Held to Maturity, Credit Loss (Expense) Benefit	3		4
Other Impairment Expense	0		0
OTTI benefit (expense) recognized in earnings	3	0	4	0
Held-to-maturity Securities [Member] | Corporate Securities [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Held to Maturity, Credit Loss (Expense) Benefit	3		4
Other Impairment Expense	0		0
OTTI benefit (expense) recognized in earnings	$ 3	$ 0	4	$ 0
Other than temporary impairment losses, investments [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
OTTI benefit (expense) recognized in earnings			$ (24,500)

Investments (Schedule of Compon

Investments (Schedule of Components of Net Realized and Unrealized Gains and Losses Excluding OTTI (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Gain (Loss) on Securities [Line Items]
Net realized gains (losses) on disposals of securities (excluding OTTI)	$ 573	$ 20,425	$ 7,288	$ 26,752
OTTI benefit (expense)	2,810	(2,291)	(24,486)	(3,366)
Net realized gains (losses)	3,383	18,134	(17,198)	23,386
Total unrealized gains (losses) recognized in income on equity securities	4,338	(20,317)	(7,098)	(8,091)
Total net realized and unrealized investment gains (losses)	7,721	(2,183)	(24,296)	15,295
Increase in net realized and unrealized investment gains	9,900
Unrealized (Gain) Loss on Equity Securities Sold	0	(21,426)	3	(9,896)
Fixed Income Securities [Member]
Gain (Loss) on Securities [Line Items]
Net realized gains (losses) on disposals of securities (excluding OTTI)	561	(1,141)	7,137	2,063
Commercial Mortgage Loans [Member]
Gain (Loss) on Securities [Line Items]
Net realized gains (losses) on disposals of securities (excluding OTTI)	1	0	2	0
Equity Securities [Member]
Gain (Loss) on Securities [Line Items]
Net realized gains (losses) on disposals of securities (excluding OTTI)	0	21,602	(3)	24,733
Unrealized (Gain) Loss on Equity Securities Sold		21,400
Short-Term Investments [Member]
Gain (Loss) on Securities [Line Items]
Net realized gains (losses) on disposals of securities (excluding OTTI)	11	(36)	157	(21)
Other Investments [Member]
Gain (Loss) on Securities [Line Items]
Net realized gains (losses) on disposals of securities (excluding OTTI)	$ 0	$ 0	$ (5)	$ (23)

Investments (Unrealized Gains (

Investments (Unrealized Gains (Losses) on Equity Securities) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Gain (Loss) on Securities [Line Items]
Unrealized gains (losses) recognized in income on equity securities on securities remaining in our portfolio at September 30, 2020	$ 4,338	$ 1,109	$ (7,101)	$ 1,805
Unrealized gains (losses) recognized in income on equity securities on securities sold in each respective period	0	(21,426)	3	(9,896)
Total unrealized gains (losses) recognized in income on equity securities	$ 4,338	$ (20,317)	$ (7,098)	$ (8,091)

Investments (Net Realized Gains

Investments (Net Realized Gains (Losses) on Disposals) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Schedule of Realized Gains (Losses) on Disposals Excluding OTTI [Line Items]
HTM gains (losses)	$ 1	$ 0	$ 2	$ 1
CMLs gains	1	0	2	0
CMLs losses	0	0	0	0
Equity securities Gains	0	21,630	0	24,868
Equity securities Losses	0	(28)	(3)	(135)
Short-term investments Gains	18	2	355	18
Short-term investments Losses	(7)	(38)	(198)	(39)
Other investments Gains	0	0	0	7
Other investments Losses	0	0	(5)	(30)
Net realized investment gains on disposals	573	20,425	7,288	26,752
Gain (Loss) on Investments [Member]
Schedule of Realized Gains (Losses) on Disposals Excluding OTTI [Line Items]
HTM gains (losses)	0	0	0	(15)
Available-for-sale Securities
Schedule of Realized Gains (Losses) on Disposals Excluding OTTI [Line Items]
AFS fixed income securities Gains	2,955	1,078	14,770	5,565
AFS fixed income securities Losses	$ (2,395)	$ (2,219)	$ (7,635)	$ (3,488)

Indebtedness (Schedule of Outst

Indebtedness (Schedule of Outstanding Debt) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Unamortized debt issuance costs	$ 3,485
Unamortized debt discount	6,373
Short-term Debt	167,000		$ 0
Long-term Debt	550,566		550,597
Finance lease liabilities	424		737
Total debt	$ 717,566		550,597
Three Point Zero Three Percent Borrowing From Federal Home Loan Bank Due December 16, 2026 [Member]
Debt Instrument [Line Items]
Interest Rate	3.03%
Original Amount	$ 60,000
Unamortized debt issuance costs	0
Unamortized debt discount	0
Long Term Debt Excluding Debt Discount And Debt Issuance Costs	$ 60,000		60,000
One Point Fifty Six Percent Borrowing From Federal Home Loan Bank Due August 16, 2021 [Member]
Debt Instrument [Line Items]
Interest Rate	1.56%
Original Amount	$ 25,000
Unamortized debt issuance costs	0
Unamortized debt discount	0
Long Term Debt Excluding Debt Discount And Debt Issuance Costs	$ 25,000		25,000
One Point Sixty One Percent Borrowing From Federal Home Loan Bank Due July 21, 2021 [Member]
Debt Instrument [Line Items]
Interest Rate	1.61%
Original Amount	$ 25,000
Unamortized debt issuance costs	0
Unamortized debt discount	0
Long Term Debt Excluding Debt Discount And Debt Issuance Costs	$ 25,000		25,000
Six Point Seventy Percent Senior Notes [Member]
Debt Instrument [Line Items]
Interest Rate	6.70%
Original Amount	$ 100,000
Unamortized debt issuance costs	329
Unamortized debt discount	505
Long Term Debt Excluding Debt Discount And Debt Issuance Costs	$ 99,166		99,125
Seven Point Twenty Five Percent Senior Notes [Member]
Debt Instrument [Line Items]
Interest Rate	7.25%
Original Amount	$ 50,000
Unamortized debt issuance costs	170
Unamortized debt discount	87
Long Term Debt Excluding Debt Discount And Debt Issuance Costs	$ 49,743		49,725
Five Point Three Hundred Seventy Five Senior Notes [Member]
Debt Instrument [Line Items]
Interest Rate	5.375%
Original Amount	$ 300,000
Unamortized debt issuance costs	2,986
Unamortized debt discount	5,781
Long Term Debt Excluding Debt Discount And Debt Issuance Costs	291,233		291,010
Long-term Debt
Debt Instrument [Line Items]
Unamortized debt issuance costs	3,485
Unamortized debt discount	6,373
Long-term Debt	$ 550,566		550,597
Zero Point Fifty Eight Percent Borrowing from FHLBI Due December 14, 2020. [Member]
Debt Instrument [Line Items]
Interest Rate	0.58%
Unamortized debt issuance costs	$ 0
Unamortized debt discount	0
Short-term Debt	$ 67,000		0
Zero Point Thirty Six Percent Borrowing from FHLBNY Due November 16, 2020 [Member]
Debt Instrument [Line Items]
Interest Rate	0.36%
Unamortized debt issuance costs	$ 0
Unamortized debt discount	0
Short-term Debt	100,000		0
Short-term Debt
Debt Instrument [Line Items]
Unamortized debt issuance costs	0
Unamortized debt discount	0
Short-term Debt	$ 167,000	$ 302,000	$ 0

Indebtedness (Short Term Debt A

Indebtedness (Short Term Debt Activity) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Short-term Debt [Line Items]
Short-term Debt	$ 167,000		$ 0
Short-term Debt [Member]
Short-term Debt [Line Items]
Short-term Debt	167,000	$ 302,000	0
Zero Point Fifty Eight Percent Borrowing from FHLBI Due December 14, 2020. [Member]
Short-term Debt [Line Items]
Short-term Debt	67,000		0
Zero Point Thirty Six Percent Borrowing from FHLBNY Due November 16, 2020 [Member]
Short-term Debt [Line Items]
Short-term Debt	$ 100,000		$ 0
Federal Home Loan Bank, Advances, Interest Rate	0.36%
Selective Insurance Group [Member]
Short-term Debt [Line Items]
Line of Credit	$ 50,000
Line of Credit Interest Rate	2.244%
Selective Insurance Company of South Carolina [Member] | Zero Point Fifty Eight Percent Borrowing from FHLBI Due December 14, 2020. [Member]
Short-term Debt [Line Items]
Federal Home Loan Bank Advances	$ 39,000
Federal Home Loan Bank, Advances, Interest Rate	0.58%
Selective Insurance Company of the Southeast [Member] | Zero Point Fifty Eight Percent Borrowing from FHLBI Due December 14, 2020. [Member]
Short-term Debt [Line Items]
Federal Home Loan Bank Advances	$ 28,000
Federal Home Loan Bank, Advances, Interest Rate	0.58%
Selective Insurance Company of America [Member] | Zero Point Sixty Eight Percent Borrowing from FHLBNY Due September 18, 2020. [Member]
Short-term Debt [Line Items]
Federal Home Loan Bank Advances	$ 85,000
Federal Home Loan Bank, Advances, Interest Rate	0.68%
Selective Insurance Company of America [Member] | Zero Point Thirty Six Percent Borrowing from FHLBNY Due November 16, 2020. [Member]
Short-term Debt [Line Items]
Federal Home Loan Bank Advances	$ 100,000
Federal Home Loan Bank, Advances, Interest Rate	0.78%
Selective Insurance Company of America [Member] | One Point Eighty One Percent Borrowing from FHLBNY Due March 18, 2020 [Member]
Short-term Debt [Line Items]
Federal Home Loan Bank, Advances, Interest Rate	1.81%

Fair Value Measurements (Carryi

Fair Value Measurements (Carrying Values and Estimated Fair Values of Financial Liabilities) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt	$ 167,000		$ 0
Short-term Debt, Fair Value	167,055		0
Finance lease liabilities	424		737
Long-term debt	550,566		550,597
Long-term debt, fair value	682,253		659,272
Unamortized debt issuance costs	(3,485)
Seven Point Twenty Five Percent Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	67,350		66,365
Unamortized debt issuance costs	(170)
Seven Point Twenty Five Percent Senior Notes [Member] | Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	49,913		49,910
Six Point Seventy Percent Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	130,651		123,104
Unamortized debt issuance costs	(329)
Six Point Seventy Percent Senior Notes [Member] | Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	99,495		99,480
Five Point Three Hundred Seventy Five Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	365,756		357,025
Unamortized debt issuance costs	(2,986)
Five Point Three Hundred Seventy Five Senior Notes [Member] | Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	294,219		294,157
One Point Sixty One Percent Borrowing From Federal Home Loan Bank Due July 21, 2021 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	25,255		24,901
Unamortized debt issuance costs	0
One Point Sixty One Percent Borrowing From Federal Home Loan Bank Due July 21, 2021 [Member] | Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	25,000		25,000
One Point Fifty Six Percent Borrowing From Federal Home Loan Bank Due August 16, 2021 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	25,269		24,875
Unamortized debt issuance costs	0
One Point Fifty Six Percent Borrowing From Federal Home Loan Bank Due August 16, 2021 [Member] | Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	25,000		25,000
Three Point Zero Three Percent Borrowing From Federal Home Loan Bank Due December 16, 2026 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	67,972		63,002
Unamortized debt issuance costs	0
Three Point Zero Three Percent Borrowing From Federal Home Loan Bank Due December 16, 2026 [Member] | Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	60,000		60,000
Long Term Debt Excluding Issuance Costs and Finance Lease Obligations [Member] | Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	553,627		553,547
Unamortized Debt Issuance Costs [Member] | Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unamortized debt issuance costs	(3,485)		(3,687)
Zero Point Thirty Six Percent Borrowing from FHLBNY Due November 16, 2020 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt	100,000		0
Short-term Debt, Fair Value	100,005		0
Unamortized debt issuance costs	0
Zero Point Thirty Six Percent Borrowing from FHLBNY Due November 16, 2020 [Member] | Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt	100,000		0
Zero Point Fifty Eight Percent Borrowing from FHLBI Due December 14, 2020. [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt	67,000		0
Short-term Debt, Fair Value	67,050		0
Unamortized debt issuance costs	0
Zero Point Fifty Eight Percent Borrowing from FHLBI Due December 14, 2020. [Member] | Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt	67,000		0
Short-term Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt	167,000	$ 302,000	0
Unamortized debt issuance costs	0
Short-term Debt [Member] | Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt	$ 167,000		$ 0

Fair Value Measurements (Quanti

Fair Value Measurements (Quantitative Disclosures of Fair Value Assets) (Details) - USD ($) $ in Thousands		Sep. 30, 2020	Dec. 31, 2019
AFS Fixed Income Securities		$ 6,437,537	$ 6,095,620
Equity Securities		151,824	72,937
Short-term investments		380,890	282,490
Net Asset Value	[1]	46,600	37,800
Fair Value, Recurring [Member]
AFS Fixed Income Securities		6,437,537	6,095,620
Equity Securities		151,824	72,937
Short-term investments		380,890	282,490
Total assets measured at fair value		6,970,251	6,451,047
U.S. Government and Government Agencies [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		117,529	116,186
Foreign Government [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		17,008	18,542
Obligations of States and Political Subdivisions [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		1,231,456	1,230,090
Corporate Securities [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		2,298,831	1,947,477
Collateralized Loan Obligations and Other Asset Backed Securities [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		945,582	793,012
Residential Mortgage Backed Securities [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		1,182,957	1,451,969
Commercial Mortgage Backed Securities [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		644,174	538,344
Common Stock [Member] | Fair Value, Recurring [Member]
Equity Securities	[1]	150,153	69,900
Preferred Stock [Member] | Fair Value, Recurring [Member]
Equity Securities		1,671	3,037
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		43,287	44,718
Equity Securities		105,274	35,182
Short-term investments		379,317	265,306
Total assets measured at fair value		527,878	345,206
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | U.S. Government and Government Agencies [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		43,287	41,083
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Foreign Government [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		0	0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Obligations of States and Political Subdivisions [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		0	0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Corporate Securities [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		0	0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Collateralized Loan Obligations and Other Asset Backed Securities [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		0	3,635
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Residential Mortgage Backed Securities [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		0	0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Commercial Mortgage Backed Securities [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		0	0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Common Stock [Member] | Fair Value, Recurring [Member]
Equity Securities	[1]	103,603	32,145
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Preferred Stock [Member] | Fair Value, Recurring [Member]
Equity Securities		1,671	3,037
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		6,309,040	6,016,817
Equity Securities		0	0
Short-term investments		1,573	17,184
Total assets measured at fair value		6,310,613	6,034,001
Significant Other Observable Inputs (Level 2) [Member] | U.S. Government and Government Agencies [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		74,242	75,103
Significant Other Observable Inputs (Level 2) [Member] | Foreign Government [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		17,008	18,542
Significant Other Observable Inputs (Level 2) [Member] | Obligations of States and Political Subdivisions [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		1,228,602	1,230,090
Significant Other Observable Inputs (Level 2) [Member] | Corporate Securities [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		2,261,195	1,930,426
Significant Other Observable Inputs (Level 2) [Member] | Collateralized Loan Obligations and Other Asset Backed Securities [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		900,862	772,343
Significant Other Observable Inputs (Level 2) [Member] | Residential Mortgage Backed Securities [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		1,182,957	1,451,969
Significant Other Observable Inputs (Level 2) [Member] | Commercial Mortgage Backed Securities [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		644,174	538,344
Significant Other Observable Inputs (Level 2) [Member] | Common Stock [Member] | Fair Value, Recurring [Member]
Equity Securities	[1]	0	0
Significant Other Observable Inputs (Level 2) [Member] | Preferred Stock [Member] | Fair Value, Recurring [Member]
Equity Securities		0	0
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		85,210	34,085
Equity Securities		0	0
Short-term investments		0	0
Total assets measured at fair value		85,210	34,085
Significant Unobservable Inputs (Level 3) [Member] | U.S. Government and Government Agencies [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		0	0
Significant Unobservable Inputs (Level 3) [Member] | Foreign Government [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		0	0
Significant Unobservable Inputs (Level 3) [Member] | Obligations of States and Political Subdivisions [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		2,854	0
Significant Unobservable Inputs (Level 3) [Member] | Corporate Securities [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		37,636	17,051
Significant Unobservable Inputs (Level 3) [Member] | Collateralized Loan Obligations and Other Asset Backed Securities [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		44,720	17,034
Significant Unobservable Inputs (Level 3) [Member] | Residential Mortgage Backed Securities [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		0	0
Significant Unobservable Inputs (Level 3) [Member] | Commercial Mortgage Backed Securities [Member] | Fair Value, Recurring [Member]
AFS Fixed Income Securities		0	0
Significant Unobservable Inputs (Level 3) [Member] | Common Stock [Member] | Fair Value, Recurring [Member]
Equity Securities	[1]	0	0
Significant Unobservable Inputs (Level 3) [Member] | Preferred Stock [Member] | Fair Value, Recurring [Member]
Equity Securities		$ 0	$ 0
[1]	Investments amounting to $46.6 million at September 30, 2020, and $37.8 million at December 31, 2019, were measured at fair value using net asset value per share (or its practical expedient) and are not classified in the fair value hierarchy. These investments are not redeemable and the timing of liquidations of the underlying assets is unknown at each reporting period. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to total assets measured at fair value.

Fair Value Measurements (Change

Fair Value Measurements (Change in Fair Value of Securities Using Level 3 Inputs) (Details) - Available-for-sale Securities [Member] - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Obligations of States and Political Subdivisions [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, December 31,	$ 0
Total net (losses) gains for the period included in OCI	(36)
Purchases	0
Sales	0
Issuances	0
Settlements	0
Transfers into Level 3	2,890
Transfers out of Level 3	0
Fair value, September 30	2,854
Period change unrealized (losses) gains in earnings for assets held at period end	0
Period change unrealized gains (losses) in OCI for assets held at period end	(36)
Corporate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, December 31,	17,051	$ 0
Total net (losses) gains for the period included in OCI	(2,415)	(69)
Purchases	19,002	0
Sales	0	0
Issuances	0	0
Settlements	(138)	0
Transfers into Level 3	4,592	16,419
Transfers out of Level 3	0	0
Fair value, September 30	37,636	16,350
Period change unrealized (losses) gains in earnings for assets held at period end	(456)	0
Period change unrealized gains (losses) in OCI for assets held at period end	(2,415)
Collateralized Loan Obligations and Other Asset Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, December 31,	17,034	7,409
Total net (losses) gains for the period included in OCI	732	(14)
Purchases	11,751	18,404
Sales	0	0
Issuances	0	0
Settlements	(1,030)	(105)
Transfers into Level 3	26,401	13,603
Transfers out of Level 3	(9,924)	(19,662)
Fair value, September 30	44,720	19,879
Period change unrealized (losses) gains in earnings for assets held at period end	(247)	0
Period change unrealized gains (losses) in OCI for assets held at period end	732
Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, December 31,	34,085	7,409
Total net (losses) gains for the period included in OCI	(1,719)	(83)
Purchases	30,753	18,404
Sales	0	0
Issuances	0	0
Settlements	(1,168)	(105)
Transfers into Level 3	33,883	30,022
Transfers out of Level 3	(9,924)	(19,662)
Fair value, September 30	85,210	36,229
Period change unrealized (losses) gains in earnings for assets held at period end	(703)	0
Period change unrealized gains (losses) in OCI for assets held at period end	(1,719)
Gain (Loss) on Investments [Member] | Obligations of States and Political Subdivisions [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total net (losses) gains for the period included in net income	0
Gain (Loss) on Investments [Member] | Corporate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total net (losses) gains for the period included in net income	(456)
Gain (Loss) on Investments [Member] | Collateralized Loan Obligations and Other Asset Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total net (losses) gains for the period included in net income	(247)
Gain (Loss) on Investments [Member] | Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total net (losses) gains for the period included in net income	(703)
Net Investment Income Earned [Member] | Obligations of States and Political Subdivisions [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total net (losses) gains for the period included in net income	0
Net Investment Income Earned [Member] | Corporate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total net (losses) gains for the period included in net income	0	0
Net Investment Income Earned [Member] | Collateralized Loan Obligations and Other Asset Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total net (losses) gains for the period included in net income	3	244
Net Investment Income Earned [Member] | Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total net (losses) gains for the period included in net income	$ 3	$ 244

Fair Value Measurements (Quan_2

Fair Value Measurements (Quantitative Information of Our Financial Assets and Liabilities That Were Disclosed at Fair Value) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	$ 167,055	$ 0
Fixed income securities, held-to-maturity - fair value	20,213	21,975
Long-term debt, fair value	682,253	659,272
Commercial mortgage loan, fair value	30,595
Seven Point Twenty Five Percent Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	67,350	66,365
Six Point Seventy Percent Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	130,651	123,104
Five Point Three Hundred Seventy Five Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	365,756	357,025
One Point Sixty One Percent Borrowing From Federal Home Loan Bank Due July 21, 2021 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	25,255	24,901
One Point Fifty Six Percent Borrowing From Federal Home Loan Bank Due August 16, 2021 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	25,269	24,875
Three Point Zero Three Percent Borrowing From Federal Home Loan Bank Due December 16, 2026 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	67,972	63,002
Long-term Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	682,253	659,272
Obligations of States and Political Subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed income securities, held-to-maturity - fair value	4,849	4,921
Corporate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed income securities, held-to-maturity - fair value	15,364	17,054
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	0
Fixed income securities, held-to-maturity - fair value	0	0
Long-term debt, fair value	0	0
Commercial mortgage loan, fair value	0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Seven Point Twenty Five Percent Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Six Point Seventy Percent Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Five Point Three Hundred Seventy Five Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | One Point Sixty One Percent Borrowing From Federal Home Loan Bank Due July 21, 2021 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | One Point Fifty Six Percent Borrowing From Federal Home Loan Bank Due August 16, 2021 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Three Point Zero Three Percent Borrowing From Federal Home Loan Bank Due December 16, 2026 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Obligations of States and Political Subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed income securities, held-to-maturity - fair value	0	0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Corporate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed income securities, held-to-maturity - fair value	0	0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	167,055
Fixed income securities, held-to-maturity - fair value	20,213	21,975
Long-term debt, fair value	682,253	659,272
Commercial mortgage loan, fair value	2,540
Significant Other Observable Inputs (Level 2) [Member] | Seven Point Twenty Five Percent Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	67,350	66,365
Significant Other Observable Inputs (Level 2) [Member] | Six Point Seventy Percent Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	130,651	123,104
Significant Other Observable Inputs (Level 2) [Member] | Five Point Three Hundred Seventy Five Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	365,756	357,025
Significant Other Observable Inputs (Level 2) [Member] | One Point Sixty One Percent Borrowing From Federal Home Loan Bank Due July 21, 2021 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	25,255	24,901
Significant Other Observable Inputs (Level 2) [Member] | One Point Fifty Six Percent Borrowing From Federal Home Loan Bank Due August 16, 2021 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	25,269	24,875
Significant Other Observable Inputs (Level 2) [Member] | Three Point Zero Three Percent Borrowing From Federal Home Loan Bank Due December 16, 2026 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	67,972	63,002
Significant Other Observable Inputs (Level 2) [Member] | Obligations of States and Political Subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed income securities, held-to-maturity - fair value	4,849	4,921
Significant Other Observable Inputs (Level 2) [Member] | Corporate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed income securities, held-to-maturity - fair value	15,364	17,054
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	0
Fixed income securities, held-to-maturity - fair value	0	0
Long-term debt, fair value	0	0
Commercial mortgage loan, fair value	28,055
Significant Unobservable Inputs (Level 3) [Member] | Seven Point Twenty Five Percent Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Significant Unobservable Inputs (Level 3) [Member] | Six Point Seventy Percent Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Significant Unobservable Inputs (Level 3) [Member] | Five Point Three Hundred Seventy Five Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Significant Unobservable Inputs (Level 3) [Member] | One Point Sixty One Percent Borrowing From Federal Home Loan Bank Due July 21, 2021 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Significant Unobservable Inputs (Level 3) [Member] | One Point Fifty Six Percent Borrowing From Federal Home Loan Bank Due August 16, 2021 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Significant Unobservable Inputs (Level 3) [Member] | Three Point Zero Three Percent Borrowing From Federal Home Loan Bank Due December 16, 2026 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
Significant Unobservable Inputs (Level 3) [Member] | Obligations of States and Political Subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed income securities, held-to-maturity - fair value	0	0
Significant Unobservable Inputs (Level 3) [Member] | Corporate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed income securities, held-to-maturity - fair value	0	0
Zero Point Thirty Six Percent Borrowing from FHLBNY Due November 16, 2020 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	100,005	0
Zero Point Thirty Six Percent Borrowing from FHLBNY Due November 16, 2020 [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	0
Zero Point Thirty Six Percent Borrowing from FHLBNY Due November 16, 2020 [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	100,005
Zero Point Thirty Six Percent Borrowing from FHLBNY Due November 16, 2020 [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	0
Zero Point Fifty Eight Percent Borrowing from FHLBI Due December 14, 2020. [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	67,050	$ 0
Zero Point Fifty Eight Percent Borrowing from FHLBI Due December 14, 2020. [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	0
Zero Point Fifty Eight Percent Borrowing from FHLBI Due December 14, 2020. [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	67,050
Zero Point Fifty Eight Percent Borrowing from FHLBI Due December 14, 2020. [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term Debt, Fair Value	$ 0

Allowance for Uncollectible P_3

Allowance for Uncollectible Premiums Receivable (Details) - USD ($) $ in Thousands		3 Months Ended	9 Months Ended
		Sep. 30, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Premiums Receiveable, Allowance for Credit Loss [Line Items]
Premium Receivable, Allowance for Credit Loss		$ 21,000	$ 21,000		$ 6,400
Premiums Receivable [Member]
Premiums Receiveable, Allowance for Credit Loss [Line Items]
Premium Receivable, Allowance for Credit Loss		21,000	21,000	$ 21,000	7,458
Current period provision for expected credit losses		802	16,369
Write-offs charged against the allowance for credit losses		(996)	(3,272)
Recoveries		$ 194	445
Allowance for credit losses, net of write-offs			$ 13,500
Premiums Receivable [Member] | Retained Earnings [Member] | Accounting Standards Update 2016-13 [Member]
Premiums Receiveable, Allowance for Credit Loss [Line Items]
Premium Receivable, Allowance for Credit Loss	[1]			0	1,058
Premiums Receivable [Member] | Accounting Standards Update 2016-13 [Member]
Premiums Receiveable, Allowance for Credit Loss [Line Items]
Premium Receivable, Allowance for Credit Loss				$ 21,000	$ 6,400
[1]	See Note 2. "Adoption of Accounting Pronouncements" above for additional information regarding our adoption of ASU 2016-13.

Reinsurance Recoverable Credit

Reinsurance Recoverable Credit Ratings (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverable, Credit Quality Indicator, Date Updated	Sep. 30, 2020
Reinsurance recoverable	$ 613,287		$ 577,635
Reinsurance Recoverable, Allowance for Credit Loss	(1,831)	$ (2,396)	(4,400)
Reinsurance recoverable, net of allowance for credit losses	611,456		$ 573,235
AM Best, A++ Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	23,727
Reinsurance Recoverable, Current	23,497
Reinsurance Recoverable, Past Due	230
AM Best, A+ Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	254,443
Reinsurance Recoverable, Current	251,341
Reinsurance Recoverable, Past Due	3,102
AM Best, A Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	105,129
Reinsurance Recoverable, Current	103,560
Reinsurance Recoverable, Past Due	1,569
AM Best, A- Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	115,196
Reinsurance Recoverable, Current	115,196
Reinsurance Recoverable, Past Due	0
AM Best, B++ Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	383
Reinsurance Recoverable, Current	95
Reinsurance Recoverable, Past Due	288
AM Best, B+ Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	10
Reinsurance Recoverable, Current	10
Reinsurance Recoverable, Past Due	0
AM Best Rated Reinsurer [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	498,888
Reinsurance Recoverable, Current	493,699
Reinsurance Recoverable, Past Due	5,189
Total federal and state pools [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	111,399
Reinsurance Recoverable, Current	111,399
Reinsurance Recoverable, Past Due	0
Other than Federal And State Pools [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	3,000
Reinsurance Recoverable, Current	2,919
Reinsurance Recoverable, Past Due	81
Total Non Rated Reinsurer [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	114,399
Reinsurance Recoverable, Current	114,318
Reinsurance Recoverable, Past Due	81
Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments, Gross [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverable, Current	608,017
Reinsurance Recoverable, Past Due	$ 5,270

Reinsurance Allowance for Credi

Reinsurance Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for credit losses, beginning of period	$ 2,396	$ 4,400
Current period provision for expected credit losses	(565)	334
Write-offs charged against the allowance for credit losses	0	0
Recoveries	0	0
Allowance for credit losses, end of period	1,831	1,831
Reinsurance Recoverable [Domain]
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for credit losses, beginning of period	2,396	1,497
Retained Earnings [Member] | Reinsurance Recoverable [Domain] | Accounting Standards Update 2016-13 [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for credit losses, beginning of period	$ 0	$ (2,903)	[1],[2]
[1]	Includes an adjustment of $2.9 million related to our adoption of ASU 2016-13. Refer to Note 2. "Adoption of Accounting Pronouncements" for additional information.
[2]	See Note 2. "Adoption of Accounting Pronouncements" for additional information regarding our adoption of ASU 2016-13.

Reinsurance (List of Direct, As

Reinsurance (List of Direct, Assumed, and Ceded Reinsurance Amounts) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Premiums earned:
Net	$ 694,541	$ 653,620	$ 1,976,915	$ 1,928,812
Loss and loss expenses incurred:
Net	447,802	398,675	1,252,075	1,166,238
Loss from Catastrophes	79,500	24,200	195,900	74,500
Direct Assumed and Ceded Reinsurance Amounts [Member]
Premiums written:
Direct	839,275	785,680	2,420,350	2,359,441
Assumed	5,450	6,882	17,902	18,770
Ceded	(125,217)	(115,634)	(346,665)	(326,939)
Net	719,508	676,928	2,091,587	2,051,272
Premiums earned:
Direct	803,957	752,872	2,292,495	2,221,257
Assumed	6,147	6,356	18,375	18,660
Ceded	(115,563)	(105,608)	(333,955)	(311,105)
Net	694,541	653,620	1,976,915	1,928,812
Loss and loss expenses incurred:
Direct	530,192	437,617	1,407,000	1,297,975
Assumed	4,232	4,362	13,430	13,975
Ceded	(86,622)	(43,304)	(168,355)	(145,712)
Net	$ 447,802	$ 398,675	$ 1,252,075	$ 1,166,238

Reinsurance (Ceded Premiums and

Reinsurance (Ceded Premiums and Losses Related to Flood Operations) (Details) - National Flood Insurance Program [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Percentage of NFIP claims ceded by federal government			100.00%
Ceded premiums written	$ (77,318)	$ (74,863)	$ (213,592)	$ (206,451)
Ceded premiums earned	(68,427)	(65,846)	(202,656)	(191,914)
Ceded loss and loss expenses incurred	$ (48,132)	$ (27,459)	$ (66,219)	$ (62,208)

Reinsurance COVID 19 Impact (De

Reinsurance COVID 19 Impact (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2020
COVID 19 Impact [Line Items]
Policyholder Premium Credit		15.00%
Non Catastrophic Loss [Member]
COVID 19 Impact [Line Items]
Direct Loss and Loss Expenses Incurred			$ (6,400)
COVID-19 [Member]
COVID 19 Impact [Line Items]
Direct Premiums Written	$ 0		(94,740)
Direct Premiums Earned	(16,303)		(84,376)
Direct Loss and Loss Expenses Incurred	(9,468)		(47,281)
Return audit and midterm endorsement premium [Member] | COVID-19 [Member]
COVID 19 Impact [Line Items]
Direct Premiums Written	0		(75,000)
Direct Premiums Earned	(16,303)		(64,636)
Direct Loss and Loss Expenses Incurred	(9,468)		(37,541)
Premium Credit [Member] | COVID-19 [Member]
COVID 19 Impact [Line Items]
Direct Premiums Written	0		(19,740)
Direct Premiums Earned	0		(19,740)
Direct Loss and Loss Expenses Incurred	0		(19,740)
COVID-19 [Member] | Commercial Property [Member]
COVID 19 Impact [Line Items]
Direct Premiums Written			0
Direct Premiums Earned			0
Direct Loss and Loss Expenses Incurred			(10,000)
Commercial & Personal Automobile [Member] | Premium Credit [Member] | COVID-19 [Member]
COVID 19 Impact [Line Items]
Direct Premiums Written	$ (19,700)
Casualty Insurance Product Line [Member] | Commercial & Personal Automobile [Member]
COVID 19 Impact [Line Items]
Direct Loss and Loss Expenses Incurred			(13,300)
Return audit and midterm endorsement premium [Member] | COVID-19 [Member]
COVID 19 Impact [Line Items]
Direct Premiums Written			$ (75,000)

Reserve for Loss and Loss Exp_3

Reserve for Loss and Loss Expense (Rollforward of Reserve for Loss and Loss Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020		Sep. 30, 2019	Jun. 30, 2020	Dec. 31, 2019
Liability for Claims and Claims Adjustment Expense [Line Items]
Gross reserve for loss and loss expense, at beginning of year			$ 4,067,163		$ 3,893,868
Less: reinsurance recoverable on unpaid loss and loss expense, at beginning of year			547,066	[1]	537,388
Net reserve for loss and loss expense, at beginning of year			3,520,097		3,356,480
Incurred loss and loss expense for claims occurring in the current year			1,295,285		1,200,878
Total incurred loss and loss expense			1,252,075		1,166,238
Paid loss and loss expense for claims occurring in the current year			421,981		384,436
Paid loss and loss expense for claims occurring in the prior years			646,974		631,589
Total paid loss and loss expense			1,068,955		1,016,025
Net reserve for loss and loss expense, at end of period	$ 3,703,217	$ 3,506,693	3,703,217		3,506,693
Add: reinsurance recoverable on unpaid loss and loss expense, at end of period	590,059	548,938	590,059		548,938
Gross reserve for loss and loss expense, at end of period	4,293,276	4,055,631	4,293,276		4,055,631
Loss Reserve for COVID-19			10,000
Loss from Catastrophes	79,500	$ 24,200	195,900		74,500
Allowance for credit losses	$ (1,831)		(1,831)			$ (2,396)	$ (4,400)
Change in Historical Claim Rate Experience [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior year development			(43,210)		(34,640)
Casualty Insurance Product Line [Member] | Change in Historical Claim Rate Experience [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior year development			(50,000)		(41,000)
Property Insurance [Member] | Change in Historical Claim Rate Experience [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior year development			6,800		6,400
Workers' Compensation Insurance [Member] | Casualty Insurance Product Line [Member] | Change in Historical Claim Rate Experience [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior year development			(40,000)		(33,000)
General Liability [Member] | Casualty Insurance Product Line [Member] | Change in Historical Claim Rate Experience [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior year development			(20,000)		(10,000)
Personal Automobile [Member] | Casualty Insurance Product Line [Member] | Change in Historical Claim Rate Experience [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior year development					$ 2,000
Commercial Automobile [Member] | Casualty Insurance Product Line [Member] | Change in Historical Claim Rate Experience [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior year development			$ 10,000
Reinsurance Recoverable [Domain]
Liability for Claims and Claims Adjustment Expense [Line Items]
Allowance for credit losses						(2,396)	(1,497)
Reinsurance Recoverable [Domain] | Retained Earnings [Member] | Accounting Standards Update 2016-13 [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Allowance for credit losses						$ 0	$ 2,903	[1],[2]
[1]	Includes an adjustment of $2.9 million related to our adoption of ASU 2016-13. Refer to Note 2. "Adoption of Accounting Pronouncements" for additional information.
[2]	See Note 2. "Adoption of Accounting Pronouncements" for additional information regarding our adoption of ASU 2016-13.

Segment Information Narrative (

Segment Information Narrative (Details)	9 Months Ended
	Sep. 30, 2020
Number of Operating Segments	4

Segment Information (Revenue by

Segment Information (Revenue by Segment) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Total net premiums earned	$ 694,541	$ 653,620	$ 1,976,915	$ 1,928,812
Miscellaneous income	6,119	3,162	12,627	8,535
Net investment income	68,185	55,826	158,596	164,949
Net realized and unrealized investment gains (losses)	7,721	(2,183)	(24,296)	15,295
Total Investments revenue	75,906	53,643	134,300	180,244
Total revenues	776,566	710,425	2,123,842	2,117,591
Standard Commercial Lines [Member]
Segment Reporting Information [Line Items]
Miscellaneous income	5,521	2,782	11,107	7,544
Total revenues	563,606	517,943	1,586,776	1,526,538
Standard Commercial Lines [Member] | Commercial Automobile [Member]
Segment Reporting Information [Line Items]
Total net premiums earned	160,937	141,182	449,162	408,706
Standard Commercial Lines [Member] | Workers Compensation [Member]
Segment Reporting Information [Line Items]
Total net premiums earned	75,595	75,478	204,207	232,657
Standard Commercial Lines [Member] | General Liability [Member]
Segment Reporting Information [Line Items]
Total net premiums earned	181,459	169,084	509,312	495,402
Standard Commercial Lines [Member] | Commercial Property [Member]
Segment Reporting Information [Line Items]
Total net premiums earned	97,997	89,215	287,279	262,418
Standard Commercial Lines [Member] | Business Owners Policies [Member]
Segment Reporting Information [Line Items]
Total net premiums earned	27,605	26,371	82,157	78,624
Standard Commercial Lines [Member] | Bonds Segment [Member]
Segment Reporting Information [Line Items]
Total net premiums earned	9,226	8,990	28,075	26,861
Standard Commercial Lines [Member] | Other Commercial [Member]
Segment Reporting Information [Line Items]
Total net premiums earned	5,266	4,841	15,477	14,326
Standard Personal Lines [Member]
Segment Reporting Information [Line Items]
Miscellaneous income	598	380	1,520	991
Total revenues	76,574	77,118	225,257	232,149
Standard Personal Lines [Member] | Personal Automobile [Member]
Segment Reporting Information [Line Items]
Total net premiums earned	42,458	43,226	123,134	129,777
Standard Personal Lines [Member] | Homeowners [Member]
Segment Reporting Information [Line Items]
Total net premiums earned	31,395	31,529	94,537	95,672
Standard Personal Lines [Member] | Other Personal [Member]
Segment Reporting Information [Line Items]
Total net premiums earned	2,123	1,983	6,066	5,709
Excess And Surplus Operations [Member]
Segment Reporting Information [Line Items]
Total revenues	60,480	61,721	177,509	178,660
Excess And Surplus Operations [Member] | Casualty Insurance Product Line [Member]
Segment Reporting Information [Line Items]
Total net premiums earned	43,650	47,171	130,444	136,455
Excess And Surplus Operations [Member] | Property Insurance [Member]
Segment Reporting Information [Line Items]
Total net premiums earned	$ 16,830	$ 14,550	$ 47,065	$ 42,205

Segment Information (Income Bef

Segment Information (Income Before and After Federal Income Tax) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Net investment income	$ 68,185	$ 55,826	$ 158,596	$ 164,949
Net realized and unrealized investment gains (losses)	7,721	(2,183)	(24,296)	15,295
Total investment segment income, before federal income tax	75,906	53,643	134,300	180,244
Tax on investment income	14,676	10,884	24,338	34,733
Total investment segment income, after federal income tax	61,230	42,759	109,962	145,511
Standard Commercial Lines [Member]
Segment Reporting Information [Line Items]
Underwriting gain (loss), before federal income tax	42,718	30,016	76,574	92,974
Underwriting gain (loss), after federal income tax	$ 33,746	$ 23,713	$ 60,493	$ 73,450
Combined ratio	92.30%	94.20%	95.10%	93.90%
ROE Contribution	5.70%	4.50%	3.50%	5.00%
Standard Personal Lines [Member]
Segment Reporting Information [Line Items]
Underwriting gain (loss), before federal income tax	$ (14,404)	$ (631)	$ (20,342)	$ 7,074
Underwriting gain (loss), after federal income tax	$ (11,379)	$ (499)	$ (16,070)	$ 5,588
Combined ratio	119.00%	100.80%	109.10%	96.90%
ROE Contribution	(1.90%)	(0.10%)	(0.90%)	0.40%
Excess And Surplus Operations [Member]
Segment Reporting Information [Line Items]
Underwriting gain (loss), before federal income tax	$ (7,277)	$ 1,916	$ (3,965)	$ 9,439
Underwriting gain (loss), after federal income tax	$ (5,748)	$ 1,514	$ (3,132)	$ 7,457
Combined ratio	112.00%	96.90%	102.20%	94.70%
ROE Contribution	(1.00%)	0.30%	(0.20%)	0.50%
Investments [Member]
Segment Reporting Information [Line Items]
ROE Contribution	9.40%	8.60%	7.50%	9.10%

Segment Information (Reconcilia

Segment Information (Reconciliation of Segment Results to Income Before Federal Income Tax (Details)) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Investment income	$ 75,906	$ 53,643	$ 134,300	$ 180,244
Interest expense	(7,781)	(7,397)	(23,310)	(26,289)
Corporate expenses	(3,905)	(6,369)	(19,310)	(28,345)
Income before federal income tax	85,257	71,178	143,947	235,097
Standard Commercial Lines [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Underwriting gain (loss), before federal income tax	42,718	30,016	76,574	92,974
Standard Personal Lines [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Underwriting gain (loss), before federal income tax	(14,404)	(631)	(20,342)	7,074
Excess And Surplus Operations [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Underwriting gain (loss), before federal income tax	(7,277)	1,916	(3,965)	9,439
Operating Segments [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total income, before federal income tax all segments	$ 96,943	$ 84,944	$ 186,567	$ 289,731

Retirement Plans (Components of

Retirement Plans (Components of Net Periodic Benefit Cost) (Details) - Pension Plan [Member] - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Interest cost		$ 2,828	$ 3,376	$ 8,484	$ 10,129
Expected return on plan assets		(5,477)	(5,278)	(16,430)	(15,835)
Amortization of unrecognized net actuarial loss		704	644	2,112	1,931
Total net periodic pension cost (benefit)	[1]	$ (1,945)	$ (1,258)	$ (5,834)	$ (3,775)
[1]	The components of net periodic pension cost (benefit) are included within "Loss and loss expense incurred" and "Other insurance expenses" on the Consolidated Statements of Income.

Retirement Plans (Weighted-Aver

Retirement Plans (Weighted-Average Expense Assumptions) (Details) - Pension Plan [Member]	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.33%	4.46%
Effective interest rate for calculation of interest cost	2.95%	4.12%
Expected return on plan assets	5.80%	6.50%

Comprehensive Income (Component

Comprehensive Income (Components of Comprehensive Income-Gross and Net of Tax) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Net income, Gross	$ 85,257	$ 71,178	$ 143,947	$ 235,097
Unrealized holding gains during the period, Gross	37,836	34,392	132,623	220,864
Non-Credit Portion of OTTI Recognized in OCI; Gross	9,239		(18,672)
Amounts reclassified into net income: HTM securities, Gross	(1)	(3)	(7)	(33)
Realized (gains) losses on disposals and intent-to-sell OTTI on AFS securities, Gross	(515)	2,821	9,126	444
Credit loss (benefit) expense recognized in OTTI, Gross	(2,853)		8,010
Total unrealized gains on investment securities, Gross	43,706	37,210	131,080	221,275
Amount reclassified into net income: Net actuarial loss, Gross	754	665	2,261	1,993
Total defined benefit pension and post-retirement benefit plans, Gross	754	665	2,261	1,993
Other comprehensive income, Gross	44,460	37,875	133,341	223,268
Comprehensive income before tax	129,717	109,053	277,288	458,365
Net income, Tax	15,382	15,028	24,653	45,333
Unrealized holding gains during the period, Tax	7,947	7,224	27,852	46,381
Non-Credit Portion of OTTI Recognized in OCI; Tax	1,940		(3,921)
Amounts reclassified into net income: HTM securities, Tax	(1)	(1)	(2)	(7)
Realized (gains) losses on disposals and intent-to-sell OTTI on AFS securities, Tax	(109)	592	1,916	93
Credit loss (benefit) expense recognized in OTTI, Tax	(599)		1,682
Total unrealized gains on investment securities, Tax	9,178	7,815	27,527	46,467
Amount reclassified into net income: Net actuarial loss, Tax	158	140	474	419
Total defined benefit pension and post-retirement benefit plans, Tax	158	140	474	419
Other comprehensive income, Tax	9,336	7,955	28,001	46,886
Comprehensive income, Tax	24,718	22,983	52,654	92,219
Net income	69,875	56,150	119,294	189,764
Unrealized holding gains arising during period, Net	29,889	27,168	104,771	174,483
Non-Credit Portion of OTTI Recognized in OCI, Net	7,299	0	(14,751)	0
Amounts reclassified into net income: HTM Securities, Net	0	(2)	(5)	(26)
Realized (gains) losses on disposals and intent-to-sell OTTI on AFS Securities, Net	(406)	2,229	7,210	351
Credit loss (benefit) expense recognized in OTTI, Net	(2,254)	0	6,328	0
Total Unrealized Gains Losses on Investment Securities, Net	34,528	29,395	103,553	174,808
Amount reclassified into net income: Net actuarial loss, Net	596	525	1,787	1,574
Total defined benefit pension and post-retirement plans, Net	596	525	1,787	1,574
Other Comprehensive Income, Net	35,124	29,920	105,340	176,382
Comprehensive Income, Net	$ 104,999	$ 86,070	$ 224,634	$ 366,146

Comprehensive Income (Compone_2

Comprehensive Income (Components of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2019			$ 81,750
Amounts reclassified from AOCI, HTM related	$ 0	$ (2)	(5)	$ (26)
Amount reclassified into net income: Net actuarial loss	596	525	1,787	1,574
Other comprehensive income	35,124	29,920	105,340	176,382
Other comprehensive income, defined pension and post retirement plans	596	525	1,787	1,574
Ending Balance, September 30, 2020	187,090		187,090
Available-for-sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2019			170,439
OCI before reclassifications			104,771
Amounts reclassified from AOCI, All Other			7,210
Other comprehensive income			111,981
Ending Balance, September 30, 2020	282,420		282,420
Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2019			170,393
OCI before reclassifications			90,020
Amounts reclassified from AOCI			13,533
Other comprehensive income			103,553
Ending Balance, September 30, 2020	273,946		273,946
Accumulated Other-than-Temporary Impairment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2019			(71)
OCI before reclassifications			(14,751)
Amounts reclassified from AOCI, OTTI			6,328
Other comprehensive income			(8,423)
Ending Balance, September 30, 2020	(8,494)		(8,494)
Accumulated Net Unrealized Investment Gain (Loss) [Member] | Held-to-maturity Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2019			25
OCI before reclassifications			0
Amounts reclassified from AOCI, HTM related			(5)
Other comprehensive income			(5)
Ending Balance, September 30, 2020	20		20
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2019			(88,643)
OCI before reclassifications, Defined Benefit Pension and Post Retirement Plans			0
Amount reclassified into net income: Net actuarial loss			1,787
Ending Balance, September 30, 2020	(86,856)		(86,856)
Accumulated other comprehensive income (loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2019			81,750
OCI before reclassifications			90,020
Amounts reclassified from AOCI			15,320
Other comprehensive income	35,124	$ 29,920	105,340	$ 176,382
Ending Balance, September 30, 2020	$ 187,090		$ 187,090

Comprehensive Income (Reclassif

Comprehensive Income (Reclassification out of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Net realized and unrealized investment gains (losses)	$ 7,721	$ (2,183)	$ (24,296)	$ 15,295
Net investment income earned	68,185	55,826	158,596	164,949
Loss and loss expense incurred	447,802	398,675	1,252,075	1,166,238
Other insurance expenses	89,530	90,234	269,477	261,975
Income before federal income tax	85,257	71,178	143,947	235,097
Total federal income tax expense	(15,382)	(15,028)	(24,653)	(45,333)
Net income	69,875	56,150	119,294	189,764
Reclassification out of AOCI
Net income	(2,064)	2,752	15,320	1,899
Pension Plan [Member] | Reclassification out of AOCI
Loss and loss expense incurred	162	146	486	436
Other insurance expenses	592	519	1,775	1,557
Income before federal income tax	754	665	2,261	1,993
Total federal income tax expense	(158)	(140)	(474)	(419)
Net income	596	525	1,787	1,574
Held-to-maturity Securities [Member] | Reclassification out of AOCI
Net realized and unrealized investment gains (losses)	4	(3)	5	(12)
Net investment income earned	(5)	0	(12)	(21)
Income before federal income tax	(1)	(3)	(7)	(33)
Total federal income tax expense	1	1	2	7
Net income	0	(2)	(5)	(26)
Available for sale securities, excluding credit losses [Member] | Reclassification out of AOCI
Net realized and unrealized investment gains (losses)	(515)	2,821	9,126	444
Income before federal income tax	(515)	2,821	9,126	444
Total federal income tax expense	109	(592)	(1,916)	(93)
Net income	(406)	2,229	7,210	351
Available for sale securities, including credit losses | Reclassification out of AOCI
Net realized and unrealized investment gains (losses)	(2,853)	0	8,010	0
Income before federal income tax	(2,853)	0	8,010	0
Total federal income tax expense	599	0	(1,682)	0
Net income	$ (2,254)	$ 0	$ 6,328	$ 0