Selective Insurance (SIGI) 10-Q 2 Aug 18 2018 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2018	Jul. 20, 2018
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q2
Entity Registrant Name	SELECTIVE INSURANCE GROUP INC
Entity Central Index Key	230,557
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock , Shares Outstanding		58,835,249

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
ASSETS
Fixed income securities, held-to-maturity – at carrying value (fair value: $43,373 – 2018; $44,100 – 2017)	$ 42,016	$ 42,129
Fixed income securities, available-for-sale – at fair value (amortized cost: $5,153,737 – 2018; $5,076,716 – 2017)	5,137,653	5,162,522
Equity securities – at fair value (cost: $150,638 – 2018)	176,578
Equity securities, available-for-sale – at fair value (cost: $143,811 – 2017)		182,705
Short-term investments (at cost which approximates fair value)	164,118	165,555
Other investments	145,203	132,268
Total investments (Note 4 and 6)	5,665,568	5,685,179
Cash	4,876	534
Restricted cash	11,604	44,176
Interest and dividends due or accrued	40,978	40,897
Premiums receivable, net of allowance for uncollectible accounts of: $10,100 – 2018; $10,000 – 2017	821,173	747,029
Reinsurance recoverable, net of allowance for uncollectible accounts of: $4,700 – 2018; $4,600 – 2017	544,979	594,832
Prepaid reinsurance premiums	157,561	153,493
Current federal income tax	0	3,243
Deferred federal income tax	51,615	31,990
Property and equipment – at cost, net of accumulated depreciation and amortization of: $220,874 – 2018; $213,227 – 2017	62,731	63,959
Deferred policy acquisition costs	248,467	235,055
Goodwill	7,849	7,849
Other assets	88,272	78,195
Total assets	7,705,673	7,686,431
Liabilities And Stockholders' Equity
Reserve for loss and loss expense (Note 8)	3,804,365	3,771,240
Unearned premiums	1,436,855	1,349,644
Long-term debt	439,331	439,116
Current federal income tax	5,090	0
Accrued salaries and benefits	85,372	131,850
Other liabilities	236,505	281,624
Total liabilities	6,007,518	5,973,474
Stockholders' Equity:
Preferred stock of $0 par value per share: Authorized shares: 5,000,000; no shares issued or outstanding	0	0
Common stock of $2 par value per share: Authorized shares: 360,000,000; Issued: 102,729,946 – 2018; 102,284,564 – 2017	205,460	204,569
Additional paid-in capital	381,641	367,717
Retained earnings	1,779,928	1,698,613
Accumulated other comprehensive (loss) income (Note 11)	(84,517)	20,170
Treasury stock – at cost (shares: 43,894,894 – 2018; 43,789,442 – 2017)	(584,357)	(578,112)
Total stockholders' equity	1,698,155	1,712,957
Commitments and contingencies
Total liabilities and stockholders' equity	$ 7,705,673	$ 7,686,431

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Fixed income securities, held-to-maturity, fair value	$ 43,373	$ 44,100
Fixed income securities, available-for-sale, amortized cost	5,153,737	5,076,716
Equity securities, cost	150,638
Equity securities, available-for-sale, cost		143,811
Premiums receivable, allowance for uncollectible accounts	10,100	10,000
Reinsurance recoverable, allowance for uncollectible accounts	4,700	4,600
Property and equipment - at cost, accumulated depreciation and amortization	$ 220,874	$ 213,227
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	102,729,946	102,284,564
Treasury stock - at cost, shares	43,894,894	43,789,442

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues:
Net premiums earned		$ 604,836	$ 568,030	$ 1,196,664	$ 1,128,884
Net investment income earned		45,553	41,430	88,784	78,849
Net realized and unrealized (losses) gains:
Net realized investment gains on disposals		54	2,951	4,785	5,381
Other-than-temporary impairments		(2,821)	(1,211)	(4,033)	(4,686)
Other-than-temporary impairments on fixed income securities recognized in other comprehensive income		0	(6)	0	(6)
Unrealized gains (losses) on equity securities	[1]	1,115	0	(12,953)	0
Total net realized and unrealized (losses) gains		(1,652)	1,734	(12,201)	689
Other income		3,179	3,291	5,358	6,532
Total revenues		651,916	614,485	1,278,605	1,214,954
Expenses:
Loss and loss expense incurred		366,328	341,559	751,269	659,031
Amortization of deferred policy acquisition costs		122,661	116,578	243,754	231,928
Other insurance expenses		80,994	82,874	164,234	164,925
Interest expense		6,125	6,081	12,277	12,187
Corporate expenses		3,283	8,464	14,615	20,380
Total expenses		579,391	555,556	1,186,149	1,088,451
Income before federal income tax		72,525	58,929	92,456	126,503
Federal income tax expense:
Current		12,782	17,785	13,215	32,058
Deferred		924	(282)	1,497	2,579
Total federal income tax expense		13,706	17,503	14,712	34,637
Net income		$ 58,819	$ 41,426	$ 77,744	$ 91,866
Earnings per share:
Basic net income		$ 1	$ 0.71	$ 1.32	$ 1.57
Diluted net income		0.99	0.70	1.30	1.55
Dividends to stockholders		$ 0.18	$ 0.16	$ 0.36	$ 0.32
[1]	Includes unrealized holding gains (losses) of: (i) $2.3 million in Second Quarter 2018 and $(2.7) million in Six Months 2018 on equity securities remaining in our portfolio as of June 30, 2018; and (ii) $(1.2) million in Second Quarter 2018 and $(10.3) million in Six Months 2018 on equity securities sold during the period.

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Net income	$ 58,819	$ 41,426	$ 77,744	$ 91,866
Unrealized holding (losses) gains arising during period	(18,955)	23,326	(86,353)	40,087
Non-credit portion of other-than-temporary impairments recognized in other comprehensive income	0	4	0	4
Amounts reclassified into net income: Held-to-maturity securities	(6)	(28)	(16)	(60)
Amounts reclassified into net income: Realized losses (gains) on disposals of available-for-sale securities	2,267	(1,225)	5,861	(244)
Total unrealized (losses) gains on investment securities	(16,694)	22,077	(80,508)	39,787
Amount reclassified into net income: Net actuarial loss	420	330	840	660
Total defined benefit pension and post-retirement plans	(420)	(330)	(840)	(660)
Other comprehensive (loss) income	(16,274)	22,407	(79,668)	40,447
Comprehensive income (loss)	$ 42,545	$ 63,833	$ (1,924)	$ 132,313

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional paid-in capital [Member]	Retained earnings [Member]	Accumulated other comprehensive income (loss) [Member]	Treasury stock [Member]
Balance at beginning of year, as adjusted				$ 1,568,881	$ (15,950)
Beginning of year at Dec. 31, 2016		$ 203,241	$ 347,295	1,568,881	(15,950)	$ (572,097)
Dividend reinvestment plan (shares: 12,373 – 2018; 15,419 – 2017)		31	693
Stock purchase and compensation plans (shares: 433,009 – 2018; 515,011 – 2017)		1,030	11,994
Net income	$ 91,866			91,866
Dividends to stockholders ($0.36 per share – 2018; $0.32 per share – 2017)				(18,927)
Other comprehensive (loss) income	40,447				40,447
Acquisition of treasury stock (shares: 105,452 – 2018; 134,910 – 2017)						(5,948)
End of period at Jun. 30, 2017	1,652,556	204,302	359,982	1,641,820	24,497	(578,045)
Cumulative effect of new accounting principle in period of adoption | Accounting Standards Update 2016-01 [Member]				0	0
Cumulative effect of new accounting principle in period of adoption | Accounting Standards Update 2018-02 [Member]				0	0
Balance at beginning of year, as adjusted				1,723,632	(4,849)
Beginning of year at Dec. 31, 2017	1,712,957	204,569	367,717	1,698,613	20,170	(578,112)
Dividend reinvestment plan (shares: 12,373 – 2018; 15,419 – 2017)		25	686
Stock purchase and compensation plans (shares: 433,009 – 2018; 515,011 – 2017)		866	13,238
Net income	77,744			77,744
Dividends to stockholders ($0.36 per share – 2018; $0.32 per share – 2017)				(21,448)
Other comprehensive (loss) income	(79,668)				(79,668)
Acquisition of treasury stock (shares: 105,452 – 2018; 134,910 – 2017)						(6,245)
End of period at Jun. 30, 2018	$ 1,698,155	$ 205,460	$ 381,641	1,779,928	(84,517)	$ (584,357)
Cumulative effect of new accounting principle in period of adoption					(25,019)
Cumulative effect of new accounting principle in period of adoption | Accounting Standards Update 2016-01 [Member]				30,726	(30,726)
Cumulative effect of new accounting principle in period of adoption | Accounting Standards Update 2018-02 [Member]				$ (5,707)	$ 5,707

Consolidated Statements of Sto7

Consolidated Statements of Stockholders' Equity (Parenthetical) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Dividend reinvestment plan, shares			12,373	15,419
Stock purchase and compensation plans, shares			433,009	515,011
Dividends to stockholders, per share	$ 0.18	$ 0.16	$ 0.36	$ 0.32
Acquisition of treasury stock, shares			105,452	134,910
Preferred stock, par value per share	$ 0	$ 0	$ 0	$ 0	$ 0
Preferred stock, shares authorized	5,000,000	5,000,000	5,000,000	5,000,000	5,000,000
Preferred stock, shares issued	0	0	0	0	0
Series A Preferred Stock [Member]
Preferred stock, par value per share	$ 0	$ 0	$ 0	$ 0
Preferred stock, shares authorized	300,000	300,000	300,000	300,000

Consolidated Statements of Cash

Consolidated Statements of Cash Flow - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Operating Activities
Net income	$ 77,744	$ 91,866
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	21,771	25,409
Stock-based compensation expense	9,636	8,372
Undistributed gains of equity method investments	(1,628)	(3,584)
Distributions in excess of current year income of equity method investments	1,450	552
Loss on disposal of fixed assets	29	998
Net realized and unrealized losses (gains)	12,201	(689)
Changes in assets and liabilities:
Increase in reserve for loss and loss expense, net of reinsurance recoverable	82,978	59,152
Increase in unearned premiums, net of prepaid reinsurance	83,143	83,633
Decrease in net federal income taxes	9,887	7,263
Increase in premiums receivable	(74,144)	(82,729)
Increase in deferred policy acquisition costs	(13,412)	(12,339)
Decrease (increase) in interest and dividends due or accrued	2	(204)
Decrease in accrued salaries and benefits	(46,478)	(29,703)
Increase in other assets	(6,550)	(3,862)
Decrease in other liabilities	(64,372)	(48,684)
Net cash provided by operating activities	92,257	95,451
Investing Activities
Purchase of fixed income securities, held-to-maturity	(3,650)	0
Purchase of fixed income securities, available-for-sale	(1,331,607)	(1,194,142)
Purchase of equity securities	(46,402)
Purchase of equity securities, available-for-sale		(22,115)
Purchase of other investments	(26,032)	(22,121)
Purchase of short-term investments	(1,462,238)	(2,259,305)
Sale of fixed income securities, available-for-sale	938,276	717,072
Sale of short-term investments	1,463,726	2,348,892
Redemption and maturities of fixed income securities, held-to-maturity	3,654	28,730
Redemption and maturities of fixed income securities, available-for-sale	311,590	300,430
Sale of equity securities	43,590
Sale of equity securities, available-for-sale		6,289
Sale of other investments	3,497	0
Distributions from other investments	15,927	9,300
Purchase of property and equipment	(6,733)	(7,047)
Net cash used in investing activities	(96,402)	(94,017)
Financing Activities
Dividends to stockholders	(20,437)	(17,922)
Acquisition of treasury stock	(6,245)	(5,948)
Net proceeds from stock purchase and compensation plans	3,930	4,045
Proceeds from borrowings	130,000	64,000
Repayments of borrowings	(130,000)	(64,000)
Repayments of capital lease obligations	(1,333)	(2,254)
Net cash used in financing activities	(24,085)	(22,079)
Net decrease in cash and restricted cash	(28,230)	(20,645)
Cash and restricted cash, beginning of year	44,710	37,405
Cash and restricted cash, end of period	$ 16,480	$ 16,760

Basis of Presentation

Basis of Presentation	6 Months Ended
	Jun. 30, 2018
Basis of Presentation And Significant Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation As used herein, the "Company,” “we,” “us,” or “our” refers to Selective Insurance Group, Inc. (the "Parent"), and its subsidiaries, except as expressly indicated or unless the context otherwise requires. Our interim unaudited consolidated financial statements (“Financial Statements”) have been prepared by us 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. The preparation of the Financial Statements in conformity with GAAP requires us to make estimates and assumptions that affect the reported financial statement balances, as well as 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. Certain amounts in our prior years' Financial Statements and related notes have been reclassified to conform to the 2018 presentation. Specifically, we reclassified restricted cash balances related to our participation in the National Flood Insurance Program ("NFIP") from other assets in our consolidated balance sheet into a separate line item on the face of that statement. Additionally, refer to Note 2. "Adoption of Accounting Pronouncements" below for a discussion of the retroactive restatements that are included in these financial statements in relation to the adoption of new accounting pronouncements for the treatment of restricted cash and distributions from equity method investments on the consolidated statements of cash flows. 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 second quarters ended June 30, 2018 (“ Second Quarter 2018 ”) and June 30, 2017 (“ Second Quarter 2017 ”) and the six-month periods ended June 30, 2018 (" Six Months 2018 ") and June 30, 2017 (" Six Months 2017 "). The Financial Statements do not include all of the information and disclosures required by GAAP and the SEC for audited annual financial statements. Results of operations for any interim period are not necessarily indicative of results for a full year. Consequently, 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, 2017 (“ 2017 Annual Report”) filed with the SEC.

Accounting Pronouncements

Accounting Pronouncements	6 Months Ended
	Jun. 30, 2018
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Accounting Pronouncements	Adoption of Accounting Pronouncements In January 2016, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2016-01, Financial Instruments - Overall: Recognition and Measurement of Financial Assets and Financial Liabilities (“ASU 2016-01”). ASU 2016-01 provides guidance to improve certain aspects of recognition, measurement, presentation, and disclosure of financial instruments. Specifically the guidance: (i) requires equity securities held in our investment portfolio to be measured at fair value with changes in fair value recognized in earnings; (ii) simplifies the impairment assessment of equity investments without readily determinable fair values by requiring a qualitative assessment to identify impairment; (iii) eliminates the requirement to disclose the methods and significant assumptions used to estimate the fair value that is required to be disclosed for financial instruments measured at amortized cost; (iv) requires the use of the exit price notion when measuring the fair value of financial instruments for disclosure purposes; and (v) clarifies that the need for a valuation allowance on a deferred tax asset related to an available-for-sale ("AFS") security should be evaluated with other deferred tax assets. We adopted ASU 2016-01 in the first quarter of 2018 and recognized a $30.7 million cumulative-effect adjustment to the opening balances of accumulated other comprehensive income ("AOCI") and retained earnings, which represents the after-tax net unrealized gain on our equity portfolio as of December 31, 2017. Additionally, beginning in the first quarter of 2018, changes in unrealized gains or losses on this portfolio are no longer recorded to AOCI, but are instead recognized in income through "Unrealized gains (losses) on equity securities" on our Consolidated Statements of Income. See Note 4 (j) below for information regarding unrealized equity gains (losses) recognized in income in Second Quarter and Six Months 2018. There were two accounting updates that we adopted with a retrospective transition in the first quarter of 2018 that related to our statements of cash flows. These accounting updates impacted our categorization of distributions from equity method investees (ASU 2016-15, Statement of Cash Flows: Classification of Certain Cash Receipts and Cash Payments ("ASU 2016-15")) and the presentation of restricted cash (ASU 2016-18, Statement of Cash Flows: Restricted Cash ("ASU 2016-18")). These ASUs are discussed below and the discussions are followed with a table presenting the impact of the prior period restatements. In August 2016, the FASB issued ASU 2016-15. As mentioned above, this ASU adds guidance on the categorization of distributions from equity method investees within the statement of cash flows. In accordance with this guidance, we made an accounting policy election to classify these distributions using the cumulative earnings approach. This election resulted in a restatement to operating and investing cash flows as outlined in the table below. ASU 2016-15 also added or clarified guidance on the cash flow classification of certain cash receipts and payments, including, but not limited to: (i) debt prepayment or debt extinguishment costs; (ii) proceeds from the settlement of corporate-owned life insurance policies, including bank-owned life insurance policies; and (iii) separately identifiable cash flows and application of the predominance principle. The updated guidance for these topics did not impact our statement of cash flows. In November 2016, the FASB issued ASU 2016-18. ASU 2016-18 requires restricted cash and restricted cash equivalents to be included with cash and cash equivalents in the reconciliation of beginning and ending cash on the statements of cash flows. This update also requires a reconciliation of the statement of the cash flows to the balance sheet if the balance sheet includes more than one line item containing cash, cash equivalents, and restricted cash. We have restricted cash related to our participation in the NFIP, which we had previously reported as part of "Other assets" on the Consolidated Balance Sheet. Beginning in the first quarter of 2018, we are reporting restricted cash in its own line item on the Consolidated Balance Sheets to aid in the reconciliation of the amounts presented on the Consolidated Statements of Cash Flows. We have also restated prior year balances on the Consolidated Balance Sheets to conform to the current year presentation. The adoption of this guidance resulted in a restatement of operating cash flows in Six Months 2017 to remove the impact of the change in restricted cash from operating activities and include the restricted cash balance in the reconciliation of beginning and ending cash balances on the Statements of Cash Flows. In addition, we have included the required reconciliation in Note 3. "Statements of Cash Flows" below. ASU 2016-15 and ASU 2016-18 resulted in the following line item restatements within operating and investing cash flows on the Statements of Cash Flows: June 30, 2017 (in thousands) Prior to Adoption After Adoption Undistributed gains of equity method investments (3,575 ) (3,584 ) Distributions in excess of current year income of equity method investments — 552 Decrease (increase) in other assets 24,953 (3,862 ) Net cash provided by operating activities 123,723 95,451 Distributions from other investments 9,843 9,300 Net cash used in investing activities (93,474 ) (94,017 ) In January 2017, the FASB issued ASU 2017-04, Intangibles-Goodwill and Other: Simplifying the Test for Goodwill Impairment (“ASU 2017-04”). ASU 2017-04 eliminates the second step of the two part goodwill impairment test, which required entities to determine the fair value of individual assets and liabilities of a reporting unit to measure the goodwill impairment. Under the new guidance, a goodwill impairment is calculated as the amount by which a reporting unit’s carrying value exceeds its fair value, not to exceed the carrying amount of goodwill. An entity still has the option to perform the qualitative assessment for a reporting unit to determine if the quantitative impairment test is necessary. The amendments in this update should be applied on a prospective basis for annual or interim goodwill impairment tests in fiscal years beginning after December 15, 2019. Early adoption is permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. We adopted ASU 2017-04 in the first quarter of 2018 and it had no impact on us. In February 2018, the FASB issued ASU 2018-02, Income Statement - Reporting Comprehensive Income ("ASU 2018-02"). ASU 2018-02 allows a one-time reclassification from AOCI to retained earnings for the stranded tax assets that were created in AOCI from the enactment of the Tax Cuts and Jobs Act of 2017 ("Tax Reform"). We adopted ASU 2018-02 in the first quarter of 2018 and recognized a $5.7 million cumulative-effect adjustment for the deferred tax charge to income in the fourth quarter of 2017 that was associated with net unrealized gains on our investment portfolio and pension plan resulting from the enactment of Tax Reform. Pronouncements to be effective in the future In June 2018, the FASB issued ASU 2018-07, Compensation - Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting ("ASU 2018-07"). The amendments in ASU 2018-07 expand the scope of Topic 718 to include share-based payment transactions for acquiring goods and services from nonemployees. ASU 2018-07 is effective for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. Early adoption is permitted. We are currently evaluating the impact of this guidance on our financial condition and results of operations.

Statements of Cash Flow

Statements of Cash Flow	6 Months Ended
	Jun. 30, 2018
Supplemental Cash Flow Information [Abstract]
Statements of Cash Flow	Statements of Cash Flows Supplemental cash flow information was as follows: Six Months ended June 30, ($ in thousands) 2018 2017 Cash paid (refunded) during the period for: Interest $ 12,064 11,963 Federal income tax 4,193 27,000 Non-cash items: Exchange of fixed income securities, AFS 32,101 1,029 Non-cash acquisition of fixed income securities, AFS 32 — Assets acquired under capital lease arrangements — 278 Non-cash purchase of property and equipment 18 — The following table provides a reconciliation of cash and restricted cash reported within the Consolidated Balance Sheets that equate to the amount reported in the Consolidated Statements of Cash Flows: ($ in thousands) June 30, 2018 December 31, 2017 Cash $ 4,876 534 Restricted cash 11,604 44,176 Total cash and restricted cash shown in the Statements of Cash Flows $ 16,480 44,710 Amounts included in restricted cash represent cash received from the NFIP, which is restricted to pay flood claims under the Write Your Own Program.

Investments

Investments	6 Months Ended
	Jun. 30, 2018
Investments [Abstract]
Investments	Investments (a) Information regarding our held-to-maturity ("HTM") fixed income securities as of June 30, 2018 and December 31, 2017 was as follows: June 30, 2018 ($ in thousands) Amortized Cost Net Unrealized Gains (Losses) Carrying Value Unrecognized Holding Gains Unrecognized Holding Losses Fair Value Obligations of states and political subdivisions $ 22,490 49 22,539 721 — 23,260 Corporate securities 19,567 (90 ) 19,477 761 (125 ) 20,113 Total HTM fixed income securities $ 42,057 (41 ) 42,016 1,482 (125 ) 43,373 December 31, 2017 ($ in thousands) Amortized Cost Net Unrealized Gains (Losses) Carrying Value Unrecognized Holding Gains Unrecognized Holding Losses Fair Value Obligations of states and political subdivisions $ 25,154 84 25,238 1,023 — 26,261 Corporate securities 16,996 (105 ) 16,891 1,003 (55 ) 17,839 Total HTM fixed income securities $ 42,150 (21 ) 42,129 2,026 (55 ) 44,100 Unrecognized holding gains and losses of HTM securities are not reflected in the Financial Statements, as they represent fair value fluctuations from the date a security is designated as HTM through the date of the balance sheet. (b) Information regarding our AFS securities as of June 30, 2018 and December 31, 2017 was as follows: June 30, 2018 ($ in thousands) Cost/ Amortized Cost Unrealized Gains Unrealized Losses Fair Value AFS fixed income securities: U.S. government and government agencies $ 39,368 291 (763 ) 38,896 Foreign government 18,024 87 (129 ) 17,982 Obligations of states and political subdivisions 1,240,487 17,622 (4,442 ) 1,253,667 Corporate securities 1,630,998 6,617 (23,131 ) 1,614,484 Collateralized loan obligations and other asset-backed securities ("CLO and other ABS") 768,466 4,948 (1,817 ) 771,597 Commercial mortgage-backed securities ("CMBS") 457,344 258 (6,009 ) 451,593 Residential mortgage-backed securities (“RMBS”) 999,050 2,726 (12,342 ) 989,434 Total AFS securities $ 5,153,737 32,549 (48,633 ) 5,137,653 December 31, 2017 ($ in thousands) Cost/ Amortized Cost Unrealized Gains Unrealized Losses Fair Value AFS fixed income securities: U.S. government and government agencies $ 49,326 647 (233 ) 49,740 Foreign government 18,040 526 (11 ) 18,555 Obligations of states and political subdivisions 1,539,307 44,245 (582 ) 1,582,970 Corporate securities 1,588,339 30,891 (1,762 ) 1,617,468 CLO and other ABS 789,152 6,508 (202 ) 795,458 CMBS 382,727 1,563 (841 ) 383,449 RMBS 709,825 6,487 (1,430 ) 714,882 Total AFS fixed income securities 5,076,716 90,867 (5,061 ) 5,162,522 AFS equity securities: Common stock 129,696 38,287 (226 ) 167,757 Preferred stock 14,115 904 (71 ) 14,948 Total AFS equity securities 143,811 39,191 (297 ) 182,705 Total AFS securities $ 5,220,527 130,058 (5,358 ) 5,345,227 Unrealized gains and losses of AFS securities represent fair value fluctuations from the later of: (i) the date a security is designated as AFS; or (ii) the date that an other-than-temporary impairment ("OTTI") charge is recognized on an AFS security, through the date of the balance sheet. These unrealized gains and losses are recorded in AOCI on the Consolidated Balance Sheets. As of the first quarter of 2018, equity securities are no longer required to be included in the table above with the adoption of new accounting guidance through which unrealized gains and losses on equity securities are no longer recognized in AOCI, but are instead recognized through income. Refer to Note 2. "Adoption of Accounting Pronouncements" for additional information regarding the adoption of ASU 2016-01. (c) The severity of impairment on securities in an unrealized/unrecognized loss position averaged approximately 1% of amortized cost at both June 30, 2018 and December 31, 2017 . Quantitative information regarding unrealized losses on our AFS portfolio is provided below. Our HTM portfolio had $0.3 million of unrealized/unrecognized losses at June 30, 2018 , and $0.1 million of unrealized/unrecognized losses at December 31, 2017 . June 30, 2018 Less than 12 months 12 months or longer Total ($ in thousands) Fair Value Unrealized Losses 1 Fair Value Unrealized Losses 1 Fair Value Unrealized 1 AFS fixed income securities: U.S. government and government agencies $ 28,005 (763 ) — — 28,005 (763 ) Foreign government 7,740 (129 ) — — 7,740 (129 ) Obligations of states and political subdivisions 342,653 (4,316 ) 3,422 (126 ) 346,075 (4,442 ) Corporate securities 1,147,312 (22,989 ) 2,762 (142 ) 1,150,074 (23,131 ) CLO and other ABS 427,307 (1,813 ) 774 (4 ) 428,081 (1,817 ) CMBS 378,523 (6,009 ) — — 378,523 (6,009 ) RMBS 739,217 (11,962 ) 10,895 (380 ) 750,112 (12,342 ) Total AFS securities $ 3,070,757 (47,981 ) 17,853 (652 ) 3,088,610 (48,633 ) December 31, 2017 Less than 12 months 12 months or longer Total ($ in thousands) Fair Value Unrealized Losses 1 Fair Value Unrealized Losses 1 Fair Value Unrealized 1 AFS fixed income securities: U.S. government and government agencies $ 23,516 (233 ) 250 — 23,766 (233 ) Foreign government 1,481 (11 ) — — 1,481 (11 ) Obligations of states and political subdivisions 107,514 (422 ) 14,139 (160 ) 121,653 (582 ) Corporate securities 238,326 (1,744 ) 3,228 (18 ) 241,554 (1,762 ) CLO and other ABS 74,977 (196 ) 1,655 (6 ) 76,632 (202 ) CMBS 154,267 (773 ) 5,214 (68 ) 159,481 (841 ) RMBS 269,485 (1,285 ) 11,200 (145 ) 280,685 (1,430 ) Total AFS fixed income securities 869,566 (4,664 ) 35,686 (397 ) 905,252 (5,061 ) AFS equity securities: Common stock 4,727 (226 ) — — 4,727 (226 ) Preferred stock 3,833 (71 ) — — 3,833 (71 ) Total AFS equity securities 8,560 (297 ) — — 8,560 (297 ) Total AFS $ 878,126 (4,961 ) 35,686 (397 ) 913,812 (5,358 ) 1 Gross unrealized losses include non-OTTI unrealized amounts and OTTI losses recognized in AOCI. The increase in the less than 12 months unrealized loss position was driven by higher interest rates, with a 65-basis point increase in 2-year U.S. Treasury Note yields and a 45-basis point increase in the 10-year U.S. Treasury Note yields during Six Months 2018 . We do not intend to sell any of the securities in the tables above, nor will we be required to sell any of these securities. Considering these factors, and in accordance with our review of these securities under our OTTI policy, as described in Note 2. “Summary of Significant Accounting Policies” within Item 8. “Financial Statements and Supplementary Data.” of our 2017 Annual Report, we have concluded that they are temporarily impaired. 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. (d) Fixed income securities at June 30, 2018 , by contractual maturity, are shown below. 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. Listed below are the contractual maturities of fixed income securities at June 30, 2018 : AFS HTM ($ in thousands) Fair Value Carrying Value Fair Value Due in one year or less $ 186,138 8,309 8,383 Due after one year through five years 2,034,623 27,160 28,544 Due after five years through 10 years 2,733,420 6,547 6,446 Due after 10 years 183,472 — — Total fixed income securities $ 5,137,653 42,016 43,373 (e) The following table summarizes our other investment portfolio by strategy: Other Investments June 30, 2018 December 31, 2017 ($ in thousands) Carrying Value Remaining Commitment Maximum Exposure to Loss 1 Carrying Value Remaining Commitment Maximum Exposure to Loss 1 Alternative Investments Private equity $ 59,681 110,833 170,514 52,251 99,026 151,277 Private credit 40,916 89,757 130,673 37,743 94,959 132,702 Real assets 23,430 36,588 60,018 25,379 27,014 52,393 Total alternative investments 124,027 237,178 361,205 115,373 220,999 336,372 Other securities 21,176 — 21,176 16,895 — 16,895 Total other investments $ 145,203 237,178 382,381 132,268 220,999 353,267 1 The maximum exposure to loss includes both the carry value of these investments and the related unfunded 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 do not have a future obligation to fund losses or debts on behalf of the investments above; however, we are contractually committed to make additional investments up to the remaining commitment outlined above. We have not provided any non-contractual financial support at any time during 2018 or 2017 . The following table sets forth gross summarized financial information for our other investments portfolio, including the portion not owned by us. The majority of these investments are carried under the equity method of accounting. The last line of the table below reflects our share of the aggregate income or loss, which is the portion included in our Financial Statements. As the majority of these investments report results to us on a one quarter lag, the summarized financial statement information for the three- and six -month periods ended March 31 is included in our Second Quarter and Six Months results. This information is as follows: Income Statement Information Quarter ended June 30, Six Months ended June 30, ($ in millions) 2018 2017 2018 2017 Net investment loss $ (6.4 ) (88.0 ) (41.8 ) (62.4 ) Realized gains (losses) 629.5 (69.2 ) 1,223.5 (304.3 ) Net change in unrealized (depreciation) appreciation (1,200.2 ) 1,328.5 (738.6 ) 1,890.0 Net (loss) gain $ (577.1 ) 1,171.3 443.1 1,523.3 Selective’s insurance subsidiaries’ alternative investments gain $ 1.9 5.2 3.5 6.8 (f) We have pledged certain AFS fixed income securities as collateral related to our relationships with the Federal Home Loan Bank of Indianapolis ("FHLBI") and the Federal Home Loan Bank of New York ("FHLBNY"). In addition, certain securities were on deposit with various state and regulatory agencies at June 30, 2018 to comply with insurance laws. We retain all rights regarding all securities pledged as collateral. The following table summarizes the market value of these securities at June 30, 2018 : ($ in millions) FHLBI Collateral FHLBNY Collateral State and Regulatory Deposits Total U.S. government and government agencies $ — — 22.3 22.3 Obligations of states and political subdivisions — — 3.1 3.1 CMBS 7.2 9.6 — 16.8 RMBS 58.2 79.8 — 138.0 Total pledged as collateral $ 65.4 89.4 25.4 180.2 (g) 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 June 30, 2018 or December 31, 2017 . (h) The components of pre-tax net investment income earned were as follows: Quarter ended June 30, Six Months ended June 30, ($ in thousands) 2018 2017 2018 2017 Fixed income securities $ 43,774 37,668 $ 85,815 74,559 Equity securities 1,820 1,419 3,797 2,887 Short-term investments 611 377 1,134 627 Other investments 2,094 5,231 3,657 6,834 Investment expenses (2,746 ) (3,265 ) (5,619 ) (6,058 ) Net investment income earned $ 45,553 41,430 $ 88,784 78,849 (i) OTTI charges were $2.8 million and $1.2 million in Second Quarter 2018 and Second Quarter 2017 , respectively, and $4.0 million and $4.7 million in Six Months 2018 and Six Months 2017 , respectively. All of the OTTI charges in 2018 and a majority of the charges in 2017 were related to securities for which we had the intent to sell, with each security type's charge not exceeding 1% of its fair value. For a discussion of our evaluation for OTTI, refer to Note 2. "Summary of Significant Accounting Policies" in Item 8. "Financial Statements and Supplementary Data." of our 2017 Annual Report. (j) Net realized and unrealized gains and losses (excluding OTTI charges) for Second Quarter and Six Months 2018 and 2017 included the following: Quarter ended June 30, Six Months ended June 30, ($ in thousands) 2018 2017 2018 2017 Net realized (losses) gains on the disposals of securities: Fixed income securities $ (1,174 ) 2,606 (4,509 ) 4,570 Equity securities 1,226 350 9,295 350 Short-term investments 2 — (1 ) — Other investments — (5 ) — 461 Net realized gains on the disposal of securities 54 2,951 4,785 5,381 OTTI charges (2,821 ) (1,217 ) (4,033 ) (4,692 ) Net realized (losses) gains (2,767 ) 1,734 752 689 Unrealized gains (losses) recognized in income on equity securities 1 1,115 — (12,953 ) — Total net realized and unrealized investment (losses) gains $ (1,652 ) 1,734 $ (12,201 ) 689 1 Includes unrealized holding gains (losses) of: (i) $2.3 million in Second Quarter 2018 and $(2.7) million in Six Months 2018 on equity securities remaining in our portfolio as of June 30, 2018 ; and (ii) $(1.2) million in Second Quarter 2018 and $(10.3) million in Six Months 2018 on equity securities sold during the period. The components of net realized gains on disposals of securities for the periods indicated were as follows: Quarter ended June 30, Six Months ended June 30, ($ in thousands) 2018 2017 2018 2017 HTM fixed income securities Gains $ — 44 2 44 Losses — — — (1 ) AFS fixed income securities Gains 1,971 2,715 4,594 6,267 Losses (3,145 ) (153 ) (9,105 ) (1,740 ) Equity securities Gains 1,226 350 9,625 350 Losses — — (330 ) — Short-term investments Gains 2 — 3 2 Losses — — (4 ) (2 ) Other investments Gains — — — 480 Losses — (5 ) — (19 ) Total net realized gains on disposals of securities $ 54 2,951 4,785 5,381 Realized gains and losses on the sale of investments are determined on the basis of the cost of the specific investments sold. Net realized gains in Second Quarter and Six Months 2018 were primarily driven by opportunistic sales in our equity portfolio and higher trading volume in our fixed income securities portfolio. Proceeds from the sales of AFS fixed income securities were $262.9 million and $122.3 million in Second Quarter 2018 and Second Quarter 2017 , respectively, and $938.3 million and $717.1 million in Six Months 2018 and Six Months 2017 , respectively. Proceeds from the sales of equity securities were $2.9 million and $0.8 million in Second Quarter 2018 and Second Quarter 2017 , respectively, and $43.6 million and $6.3 million in Six Months 2018 and Six Months 2017 , respectively.

Indebtedness Indebtedness

Indebtedness Indebtedness	6 Months Ended
	Jun. 30, 2018
Debt Disclosure [Abstract]
Debt Disclosure	Indebtedness Our long-term debt balance has not changed materially since December 31, 2017 . However, Selective Insurance Company of America ("SICA") borrowed the following short-term funds in the first quarter of 2018 from the FHLBNY: • On February 27, 2018, SICA borrowed $75 million at an interest rate of 1.75% . This borrowing was repaid on March 20, 2018; and • On March 28, 2018, SICA borrowed $55 million at an interest rate of 1.98% . This borrowing was repaid on April 18, 2018. For detailed information on our indebtedness, see Note 10. "Indebtedness" in Item 8. "Financial Statements and Supplementary Data." of our 2017 Annual Report.

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Our financial assets are measured at fair value as disclosed on the Consolidated Balance Sheets. The fair values of our long-term debt are provided in this footnote and the related carry values have changed by less than 1% during Six Months 2018 . For a discussion of the fair value and hierarchy of the 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 2017 Annual Report. The following tables provide quantitative disclosures of our financial assets that were measured and recorded at fair value at June 30, 2018 and December 31, 2017 : June 30, 2018 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 Inputs (Level 3) Description Measured on a recurring basis: AFS fixed income securities: U.S. government and government agencies $ 38,896 22,479 16,417 — Foreign government 17,982 — 17,982 — Obligations of states and political subdivisions 1,253,667 — 1,253,667 — Corporate securities 1,614,484 — 1,614,484 — CLO and other ABS 771,597 — 768,408 3,189 CMBS 451,593 — 451,593 — RMBS 989,434 — 989,434 — Total AFS fixed income securities 5,137,653 22,479 5,111,985 3,189 Equity securities: Common stock 2 172,157 145,038 — — Preferred stock 4,421 4,421 — — Total equity securities 176,578 149,459 — — Short-term investments 164,118 163,120 998 — Total assets measured at fair value $ 5,478,349 335,058 5,112,983 3,189 December 31, 2017 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 Inputs (Level 3) Description Measured on a recurring basis: AFS fixed income securities: U.S. government and government agencies $ 49,740 24,652 25,088 — Foreign government 18,555 — 18,555 — Obligations of states and political subdivisions 1,582,970 — 1,582,970 — Corporate securities 1,617,468 — 1,617,468 — CLO and other ABS 795,458 — 795,458 — CMBS 383,449 — 376,895 6,554 RMBS 714,882 — 714,882 — Total AFS fixed income securities 5,162,522 24,652 5,131,316 6,554 AFS equity securities: Common stock 2 167,757 138,640 — 5,398 Preferred stock 14,948 14,948 — — Total AFS equity securities 182,705 153,588 — 5,398 Total AFS securities 5,345,227 178,240 5,131,316 11,952 Short-term investments 165,555 165,555 — — Total assets measured at fair value $ 5,510,782 343,795 5,131,316 11,952 1 There were no transfers of securities between Level 1 and Level 2. 2 Investments amounting to $27.1 million at June 30, 2018 , and $23.7 million at December 31, 2017 , were measured at fair value using net asset value per share (or its practical expedient) and have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to total assets measured at fair value. There were no material changes in the fair value of securities measured using Level 3 prices in Six Months 2017 . The following table provides a summary of Level 3 changes in Six Months 2018 : June 30, 2018 ($ in thousands) CMBS Common Stock CLO and Other ABS Fair value, December 31, 2017 $ 6,554 5,398 — Total net (losses) gains for the period included in: Other comprehensive income ("OCI") — — — Net income — — — Purchases — — 3,189 Sales — — — Issuances — — — Settlements — — — Transfers into Level 3 — — — Transfers out of Level 3 (6,554 ) (5,398 ) — Fair value, June 30, 2018 $ — — 3,189 The following tables provide quantitative information regarding our financial assets and liabilities that were disclosed at fair value at June 30, 2018 and December 31, 2017 : June 30, 2018 Fair Value Measurements Using ($ in thousands) Assets/ Quoted Prices in Active Markets for Identical Assets/ Liabilities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Financial Assets HTM: Obligations of states and political subdivisions $ 23,260 — 23,260 — Corporate securities 20,113 — 11,628 8,485 Total HTM fixed income securities $ 43,373 — 34,888 8,485 Financial Liabilities Long-term debt: 7.25% Senior Notes $ 57,231 — 57,231 — 6.70% Senior Notes 108,453 — 108,453 — 5.875% Senior Notes 186,924 186,924 — — 1.61% borrowings from FHLBNY 23,979 — 23,979 — 1.56% borrowings from FHLBNY 23,915 — 23,915 — 3.03% borrowings from FHLBI 58,483 — 58,483 — Total long-term debt $ 458,985 186,924 272,061 — December 31, 2017 Fair Value Measurements Using ($ in thousands) Assets/ Quoted Prices in Active Markets for Identical Assets/ Liabilities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Financial Assets HTM: Obligations of states and political subdivisions $ 26,261 — 26,261 — Corporate securities 17,839 — 12,306 5,533 Total HTM fixed income securities $ 44,100 — 38,567 5,533 Financial Liabilities Long-term debt: 7.25% Senior Notes $ 61,391 — 61,391 — 6.70% Senior Notes 116,597 — 116,597 — 5.875% Senior Notes 186,332 186,332 — — 1.61% borrowings from FHLBNY 24,270 — 24,270 — 1.56% borrowings from FHLBNY 24,210 — 24,210 — 3.03% borrowings from FHLBI 60,334 — 60,334 — Total long-term debt $ 473,134 186,332 286,802 —

Reinsurance

Reinsurance	6 Months Ended
	Jun. 30, 2018
Reinsurance Disclosures [Abstract]
Reinsurance	Reinsurance 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 2017 Annual Report. Quarter ended June 30, Six Months ended June 30, ($ in thousands) 2018 2017 2018 2017 Premiums written: Direct $ 753,363 706,408 $ 1,467,597 1,390,228 Assumed 6,536 6,488 12,807 12,179 Ceded (104,651 ) (99,082 ) (200,596 ) (189,889 ) Net $ 655,248 613,814 $ 1,279,808 1,212,518 Premiums earned: Direct $ 696,723 654,588 $ 1,380,456 1,301,316 Assumed 6,612 6,063 12,736 11,842 Ceded (98,499 ) (92,621 ) (196,528 ) (184,274 ) Net $ 604,836 568,030 $ 1,196,664 1,128,884 Loss and loss expenses incurred: Direct $ 391,014 389,550 $ 811,930 731,672 Assumed 2,364 7,766 10,368 12,203 Ceded (27,050 ) (55,757 ) (71,029 ) (84,844 ) Net $ 366,328 341,559 $ 751,269 659,031 Ceded premiums and losses related to our participation in the NFIP, under which 100% of our flood premiums, losses, and loss expenses are ceded to the NFIP, are as follows: Ceded to NFIP Quarter ended June 30, Six Months ended June 30, ($ in thousands) 2018 2017 2018 2017 Ceded premiums written $ (66,341 ) (63,808 ) $ (123,010 ) (120,142 ) Ceded premiums earned (60,143 ) (57,655 ) (119,134 ) (114,932 ) Ceded loss and loss expenses incurred (10,261 ) (15,140 ) (25,980 ) (21,681 )

Reserve for Loss and Loss Expen

Reserve for Loss and Loss Expense	6 Months Ended
	Jun. 30, 2018
Insurance Loss Reserves [Abstract]
Liability for Future Policy Benefits and Unpaid Claims Disclosure	Reserve for Loss and Loss Expense The table below provides a roll forward of reserve for loss and loss expense balances: Six Months ended June 30, ($ in thousands) 2018 2017 Gross reserve for loss and loss expense, at beginning of year $ 3,771,240 3,691,719 Less: reinsurance recoverable on unpaid loss and loss expense, at beginning of year 585,855 611,200 Net reserve for loss and loss expense, at beginning of year 3,185,385 3,080,519 Incurred loss and loss expense for claims occurring in the: Current year 756,855 684,877 Prior years (5,586 ) (25,846 ) Total incurred loss and loss expense 751,269 659,031 Paid loss and loss expense for claims occurring in the: Current year 214,169 171,724 Prior years 457,441 425,521 Total paid loss and loss expense 671,610 597,245 Net reserve for loss and loss expense, at end of period 3,265,044 3,142,305 Add: Reinsurance recoverable on unpaid loss and loss expense, at end of period 539,321 588,916 Gross reserve for loss and loss expense at end of period $ 3,804,365 3,731,221 The $72.0 million increase in current year loss and loss expense incurred illustrated in the table above was primarily driven by non-catastrophe property losses, as well as an increase in exposure due to premium growth. Non-catastrophe property losses, which increased $44.0 million , to $188.7 million , in Six Months 2018 , were principally related to the early January deep freeze in our footprint states and a relatively large number of severe fire losses. Prior year development in Six Months 2018 of $5.6 million included $12.0 million of favorable casualty development partially offset by $6.4 million of unfavorable property development. The favorable casualty development included $33.0 million of development in our workers compensation line of business, partially offset by unfavorable development of $15.0 million in our commercial automobile line of business and $6.0 million in our excess and surplus ("E&S") casualty lines. Prior year development in Six Months 2017 of $25.8 million was primarily driven by favorable prior year casualty reserve development of $37.4 million in our general liability line of business and $15.3 million in our workers compensation line of business. This was partially offset by unfavorable development of $21.0 million in our commercial automobile line of business and $4.0 million in our personal automobile line of business. For a discussion of the trends and recent developments impacting these lines, refer to the "Critical Accounting Policies and Estimates" section of Item 7. "Management's Discussion and Analysis of Financial Condition and Results of Operations." in our 2017 Annual Report.

Segment Information

Segment Information	6 Months Ended
	Jun. 30, 2018
Segment Reporting [Abstract]
Segment Information	Segment Information The disaggregated results of our four reportable segments are used by senior management to manage our operations. These reportable segments are evaluated as follows: • Our Standard Commercial Lines, Standard Personal Lines, and E&S Lines are evaluated based on before and after-tax underwriting results (net premiums earned, incurred loss and loss expense, policyholder dividends, policy acquisition costs, and other underwriting expenses), and combined ratios. • Our Investments segment is evaluated based on after-tax net investment income and net realized gains and losses. In computing the results of each segment, we do not make adjustments for interest expense or corporate expenses. We do not maintain separate investment portfolios for the segments and therefore, do not allocate assets to the segments. The following summaries present revenues (net investment income and net realized and unrealized gains on investments in the case of the Investments segment) and pre-tax income for the individual segments: Revenue by Segment Quarter ended June 30, Six Months ended June 30, ($ in thousands) 2018 2017 2018 2017 Standard Commercial Lines: Net premiums earned: Commercial automobile $ 122,104 108,316 240,335 215,445 Workers compensation 80,021 79,460 158,844 158,786 General liability 153,002 141,503 302,831 281,487 Commercial property 82,162 78,052 162,488 154,443 Businessowners’ policies 25,829 24,989 51,420 49,834 Bonds 8,335 6,986 16,469 13,484 Other 4,559 4,288 8,989 8,529 Miscellaneous income 2,882 3,016 4,708 5,876 Total Standard Commercial Lines revenue 478,894 446,610 946,084 887,884 Standard Personal Lines: Net premiums earned: Personal automobile 41,810 37,663 82,252 74,613 Homeowners 32,223 32,467 64,424 65,167 Other 1,644 1,542 3,257 3,093 Miscellaneous income 297 275 649 656 Total Standard Personal Lines revenue 75,974 71,947 150,582 143,529 E&S Lines: Net premiums earned: Casualty lines 39,379 39,054 77,919 76,966 Property lines 13,768 13,710 27,436 27,037 Miscellaneous income — — 1 — Total E&S Lines revenue 53,147 52,764 105,356 104,003 Investments: Net investment income 45,553 41,430 88,784 78,849 Net realized and unrealized investment (losses) gains (1,652 ) 1,734 (12,201 ) 689 Total Investments revenue 43,901 43,164 76,583 79,538 Total revenues $ 651,916 614,485 1,278,605 1,214,954 Income Before and After Federal Income Tax Quarter ended June 30, Six Months ended June 30, ($ in thousands) 2018 2017 2018 2017 Standard Commercial Lines: Underwriting gain, before federal income tax $ 41,016 34,759 47,820 77,305 Underwriting gain, after federal income tax 32,403 22,593 37,778 50,248 Combined ratio 91.4 % 92.2 94.9 91.2 Standard Personal Lines: Underwriting gain (loss), before federal income tax $ 4,805 (5,768 ) 3,299 (662 ) Underwriting gain (loss), after federal income tax 3,796 (3,749 ) 2,606 (430 ) Combined ratio 93.7 % 108.0 97.8 100.5 E&S Lines: Underwriting (loss) gain, before federal income tax $ (7,789 ) 1,319 (8,354 ) 2,889 Underwriting (loss) gain, after federal income tax (6,154 ) 857 (6,600 ) 1,878 Combined ratio 114.7 % 97.5 107.9 97.2 Investments: Net investment income $ 45,553 41,430 88,784 78,849 Net realized and unrealized investment (losses) gains (1,652 ) 1,734 (12,201 ) 689 Total investment income, before federal income tax 43,901 43,164 76,583 79,538 Tax on investment income 7,617 11,734 12,843 21,336 Total investment income, after federal income tax $ 36,284 31,430 63,740 58,202 Reconciliation of Segment Results to Income Before Federal Income Tax Quarter ended June 30, Six Months ended June 30, ($ in thousands) 2018 2017 2018 2017 Underwriting gain (loss) Standard Commercial Lines $ 41,016 34,759 47,820 77,305 Standard Personal Lines 4,805 (5,768 ) 3,299 (662 ) E&S Lines (7,789 ) 1,319 (8,354 ) 2,889 Investment income 43,901 43,164 76,583 79,538 Total all segments 81,933 73,474 119,348 159,070 Interest expense (6,125 ) (6,081 ) (12,277 ) (12,187 ) Corporate expenses (3,283 ) (8,464 ) (14,615 ) (20,380 ) Income, before federal income tax $ 72,525 58,929 92,456 126,503

Retirement Plans

Retirement Plans	6 Months Ended
	Jun. 30, 2018
Retirement Benefits [Abstract]
Retirement Plans	Retirement Plans SICA's primary pension plan 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 concerning SICA's retirement plans, refer to Note 14. “Retirement Plans” in Item 8. “Financial Statements and Supplementary Data.” of our 2017 Annual Report. The following tables provide information regarding the Pension Plan: Pension Plan Pension Plan Quarter ended June 30, Six Months ended June 30, ($ in thousands) 2018 2017 2018 2017 Net Periodic Benefit Cost: Interest cost $ 3,095 3,110 6,190 6,221 Expected return on plan assets (5,681 ) (4,855 ) (11,363 ) (9,709 ) Amortization of unrecognized net actuarial loss 493 482 987 963 Total net periodic benefit cost 1 $ (2,093 ) (1,263 ) (4,186 ) (2,525 ) 1 The components of net periodic benefit cost are included within "Loss and loss expense incurred" and "Other insurance expenses" on the Consolidated Statements of Income. Pension Plan Six Months ended June 30, 2018 2017 Weighted-Average Expense Assumptions: Discount rate 3.78 % 4.41 % Effective interest rate for calculation of interest cost 3.46 3.84 Expected return on plan assets 6.36 6.24

Comprehensive Income

Comprehensive Income	6 Months Ended
	Jun. 30, 2018
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Comprehensive Income	Comprehensive Income The components of comprehensive income, both gross and net of tax, for Second Quarter and Six Months 2018 and 2017 are as follows: Second Quarter 2018 ($ in thousands) Gross Tax Net Net income $ 72,525 13,706 58,819 Components of other comprehensive loss: Unrealized losses on investment securities : Unrealized holding losses during period (23,993 ) (5,038 ) (18,955 ) Amounts reclassified into net income: HTM securities (8 ) (2 ) (6 ) Realized losses on disposals of AFS securities 2,870 603 2,267 Total unrealized losses on investment securities (21,131 ) (4,437 ) (16,694 ) Defined benefit pension and post-retirement plans: Amounts reclassified into net income: Net actuarial loss 531 111 420 Total defined benefit pension and post-retirement plans 531 111 420 Other comprehensive loss (20,600 ) (4,326 ) (16,274 ) Comprehensive income $ 51,925 9,380 42,545 Second Quarter 2017 ($ in thousands) Gross Tax Net Net income $ 58,929 17,503 41,426 Components of OCI: Unrealized gains on investment securities : Unrealized holding gains during period 35,887 12,561 23,326 Non-credit portion of OTTI recognized in OCI 6 2 4 Amounts reclassified into net income: HTM securities (43 ) (15 ) (28 ) Realized gains on disposals of AFS securities (1,885 ) (660 ) (1,225 ) Total unrealized gains on investment securities 33,965 11,888 22,077 Defined benefit pension and post-retirement plans: Amounts reclassified into net income: Net actuarial loss 508 178 330 Total defined benefit pension and post-retirement plans 508 178 330 Other comprehensive income 34,473 12,066 22,407 Comprehensive income $ 93,402 29,569 63,833 Six Months 2018 ($ in thousands) Gross Tax Net Net income $ 92,456 14,712 77,744 Components of other comprehensive loss: Unrealized losses on investment securities : Unrealized holding losses during period (109,308 ) (22,955 ) (86,353 ) Amounts reclassified into net income: HTM securities (20 ) (4 ) (16 ) Realized losses on disposals of AFS securities 7,419 1,558 5,861 Total unrealized losses on investment securities (101,909 ) (21,401 ) (80,508 ) Defined benefit pension and post-retirement plans: Amounts reclassified into net income: Net actuarial loss 1,063 223 840 Total defined benefit pension and post-retirement plans 1,063 223 840 Other comprehensive loss (100,846 ) (21,178 ) (79,668 ) Comprehensive loss $ (8,390 ) (6,466 ) (1,924 ) Six Months 2017 ($ in thousands) Gross Tax Net Net income $ 126,503 34,637 91,866 Components of OCI: Unrealized gains on investment securities : Unrealized holding gains during period 61,672 21,585 40,087 Non-credit portion of OTTI recognized in OCI 6 2 4 Amounts reclassified into net income: HTM securities (92 ) (32 ) (60 ) Realized gains on disposals of AFS securities (375 ) (131 ) (244 ) Total unrealized gains on investment securities 61,211 21,424 39,787 Defined benefit pension and post-retirement plans: Amounts reclassified into net income: Net actuarial loss 1,015 355 660 Total defined benefit pension and post-retirement plans 1,015 355 660 Other comprehensive income 62,226 21,779 40,447 Comprehensive income $ 188,729 56,416 132,313 The balances of, and changes in, each component of AOCI (net of taxes) as of June 30, 2018 were as follows: June 30, 2018 Defined Benefit Pension and Post-Retirement Plans Net Unrealized Gains (Losses) on Investment Securities Total AOCI ($ in thousands) OTTI Related HTM Related All Other Investments Subtotal Balance, December 31, 2017 $ (59 ) (14 ) 80,648 80,575 (60,405 ) 20,170 Cumulative effect adjustments (12 ) (2 ) (12,792 ) (12,806 ) (12,213 ) (25,019 ) Balance, December 31, 2017 as adjusted (71 ) (16 ) 67,856 67,769 (72,618 ) (4,849 ) OCI before reclassifications — — (86,353 ) (86,353 ) — (86,353 ) Amounts reclassified from AOCI — (16 ) 5,861 5,845 840 6,685 Net current period OCI — (16 ) (80,492 ) (80,508 ) 840 (79,668 ) Balance, June 30, 2018 $ (71 ) (32 ) (12,636 ) (12,739 ) (71,778 ) (84,517 ) The reclassifications out of AOCI were as follows: Quarter ended June 30, Six Months ended June 30, Affected Line Item in the Unaudited Consolidated Statements of Income ($ in thousands) 2018 2017 2018 2017 HTM related Unrealized losses on HTM disposals $ (7 ) 17 (6 ) 30 Net realized and unrealized (losses) gains Amortization of net unrealized gains on HTM securities (1 ) (60 ) (14 ) (122 ) Net investment income earned (8 ) (43 ) (20 ) (92 ) Income before federal income tax 2 15 4 32 Total federal income tax expense (6 ) (28 ) (16 ) (60 ) Net income Realized losses (gains) on AFS and OTTI Realized losses (gains) on AFS disposals and OTTI 2,870 (1,885 ) 7,419 (375 ) Net realized and unrealized (losses) gains 2,870 (1,885 ) 7,419 (375 ) Income before federal income tax (603 ) 660 (1,558 ) 131 Total federal income tax expense 2,267 (1,225 ) 5,861 (244 ) Net income Defined benefit pension and post-retirement life plans Net actuarial loss 113 111 225 221 Loss and loss expense incurred 418 397 838 794 Other insurance expenses Total defined benefit pension and post-retirement life 531 508 1,063 1,015 Income before federal income tax (111 ) (178 ) (223 ) (355 ) Total federal income tax expense 420 330 840 660 Net income Total reclassifications for the period $ 2,681 (923 ) 6,685 356 Net income

Federal Income Taxes

Federal Income Taxes	6 Months Ended
	Jun. 30, 2018
Income Tax Disclosure [Abstract]
Income Tax Disclosure	Federal Income Taxes (a) On December 22, 2017, Tax Reform was signed into law, which among other implications, reduced our statutory corporate tax rate from 35% to 21% beginning with our 2018 tax year. We continue to provide provisional amounts for loss reserve discounting because the Internal Revenue Service ("IRS") has not yet issued guidance with regard to the discount rates to be used under Tax Reform. For additional information, refer to Note 13. "Federal Income Taxes" in Item 8. "Financial Statements and Supplementary Data." of our 2017 Annual Report. During 2018, we will continue to monitor IRS guidance to complete the analysis of loss reserve discounting. (b) A reconciliation of federal income tax on income at the corporate rate to the effective tax rate is as follows: Quarter ended June 30, Six Months ended June 30, ($ in thousands) 2018 2017 2018 2017 Statutory tax rate 21 % 35 21 35 Tax at statutory rate $ 15,231 20,625 19,416 44,276 Tax-advantaged interest (1,393 ) (2,757 ) (2,904 ) (5,564 ) Dividends received deduction (210 ) (625 ) (336 ) (956 ) Stock-based compensation (82 ) (374 ) (2,548 ) (3,323 ) Other 160 634 1,084 204 Federal income tax expense $ 13,706 17,503 14,712 34,637

Litigation

Litigation	6 Months Ended
	Jun. 30, 2018
Loss Contingency, Information about Litigation Matters [Abstract]
Litigation	Litigation In the ordinary course of conducting business, we are named as defendants in various legal proceedings. Most of these proceedings are claims litigation involving our ten insurance subsidiaries ("Insurance Subsidiaries") as either: (i) liability insurers defending or providing indemnity for third-party claims brought against our customers; or (ii) insurers defending first-party coverage claims brought against them. We account for such activity through the establishment of unpaid loss and loss expense reserves. We expect that any potential ultimate liability in such ordinary course claims litigation will not be material to our consolidated financial condition, results of operations, or cash flows after consideration of provisions made for potential losses and costs of defense. From time to time, our Insurance Subsidiaries also are named as defendants in other legal actions, some of which assert claims for substantial amounts. These actions include, among others, putative class actions seeking certification of a state or national class. Such putative class actions have alleged, for example, improper reimbursement of medical providers paid under workers compensation and personal and commercial automobile insurance policies. Similarly, our Insurance Subsidiaries are also named from time-to-time in individual actions seeking extra-contractual damages, punitive damages, or penalties, some of which allege bad faith in the handling of insurance claims. We believe that we have valid defenses to these cases. We expect that any potential ultimate liability in any such lawsuit will not be material to our consolidated financial condition, after consideration of provisions made for estimated losses. Nonetheless, given the inherent unpredictability of litigation and the large or indeterminate amounts sought in certain of these actions, an adverse outcome in certain matters could possibly have a material adverse effect on our consolidated results of operations or cash flows in particular quarterly or annual periods. As of June 30, 2018 , we do not believe the Company was involved in any legal action that could have a material adverse effect on our consolidated financial condition, results of operations, or cash flows.

Accounting Pronouncements (Tabl

Accounting Pronouncements (Tables)	6 Months Ended
	Jun. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Schedule of New Accounting Pronouncements and Changes in Accounting Principles	June 30, 2017 (in thousands) Prior to Adoption After Adoption Undistributed gains of equity method investments (3,575 ) (3,584 ) Distributions in excess of current year income of equity method investments — 552 Decrease (increase) in other assets 24,953 (3,862 ) Net cash provided by operating activities 123,723 95,451 Distributions from other investments 9,843 9,300 Net cash used in investing activities (93,474 ) (94,017 )

Statements of Cash Flow (Tables

Statements of Cash Flow (Tables)	6 Months Ended
	Jun. 30, 2018
Supplemental Cash Flow Information [Abstract]
Schedule of Cash Flow, Supplemental Disclosures	Six Months ended June 30, ($ in thousands) 2018 2017 Cash paid (refunded) during the period for: Interest $ 12,064 11,963 Federal income tax 4,193 27,000 Non-cash items: Exchange of fixed income securities, AFS 32,101 1,029 Non-cash acquisition of fixed income securities, AFS 32 — Assets acquired under capital lease arrangements — 278 Non-cash purchase of property and equipment 18 —
Schedule of Cash and Restricted Cash	($ in thousands) June 30, 2018 December 31, 2017 Cash $ 4,876 534 Restricted cash 11,604 44,176 Total cash and restricted cash shown in the Statements of Cash Flows $ 16,480 44,710

Investments (Tables)

Investments (Tables)	6 Months Ended
	Jun. 30, 2018
Investments [Line Items]
Schedule of Held-to-maturity Securities	June 30, 2018 ($ in thousands) Amortized Cost Net Unrealized Gains (Losses) Carrying Value Unrecognized Holding Gains Unrecognized Holding Losses Fair Value Obligations of states and political subdivisions $ 22,490 49 22,539 721 — 23,260 Corporate securities 19,567 (90 ) 19,477 761 (125 ) 20,113 Total HTM fixed income securities $ 42,057 (41 ) 42,016 1,482 (125 ) 43,373 December 31, 2017 ($ in thousands) Amortized Cost Net Unrealized Gains (Losses) Carrying Value Unrecognized Holding Gains Unrecognized Holding Losses Fair Value Obligations of states and political subdivisions $ 25,154 84 25,238 1,023 — 26,261 Corporate securities 16,996 (105 ) 16,891 1,003 (55 ) 17,839 Total HTM fixed income securities $ 42,150 (21 ) 42,129 2,026 (55 ) 44,100
Schedule of Available-for-sale Securities	June 30, 2018 ($ in thousands) Cost/ Amortized Cost Unrealized Gains Unrealized Losses Fair Value AFS fixed income securities: U.S. government and government agencies $ 39,368 291 (763 ) 38,896 Foreign government 18,024 87 (129 ) 17,982 Obligations of states and political subdivisions 1,240,487 17,622 (4,442 ) 1,253,667 Corporate securities 1,630,998 6,617 (23,131 ) 1,614,484 Collateralized loan obligations and other asset-backed securities ("CLO and other ABS") 768,466 4,948 (1,817 ) 771,597 Commercial mortgage-backed securities ("CMBS") 457,344 258 (6,009 ) 451,593 Residential mortgage-backed securities (“RMBS”) 999,050 2,726 (12,342 ) 989,434 Total AFS securities $ 5,153,737 32,549 (48,633 ) 5,137,653 December 31, 2017 ($ in thousands) Cost/ Amortized Cost Unrealized Gains Unrealized Losses Fair Value AFS fixed income securities: U.S. government and government agencies $ 49,326 647 (233 ) 49,740 Foreign government 18,040 526 (11 ) 18,555 Obligations of states and political subdivisions 1,539,307 44,245 (582 ) 1,582,970 Corporate securities 1,588,339 30,891 (1,762 ) 1,617,468 CLO and other ABS 789,152 6,508 (202 ) 795,458 CMBS 382,727 1,563 (841 ) 383,449 RMBS 709,825 6,487 (1,430 ) 714,882 Total AFS fixed income securities 5,076,716 90,867 (5,061 ) 5,162,522 AFS equity securities: Common stock 129,696 38,287 (226 ) 167,757 Preferred stock 14,115 904 (71 ) 14,948 Total AFS equity securities 143,811 39,191 (297 ) 182,705 Total AFS securities $ 5,220,527 130,058 (5,358 ) 5,345,227
Schedule of Fair Value and Gross Pre-Tax Net Unrealized/Unrecognized Loss of Securities by Length of Time, AFS	June 30, 2018 Less than 12 months 12 months or longer Total ($ in thousands) Fair Value Unrealized Losses 1 Fair Value Unrealized Losses 1 Fair Value Unrealized 1 AFS fixed income securities: U.S. government and government agencies $ 28,005 (763 ) — — 28,005 (763 ) Foreign government 7,740 (129 ) — — 7,740 (129 ) Obligations of states and political subdivisions 342,653 (4,316 ) 3,422 (126 ) 346,075 (4,442 ) Corporate securities 1,147,312 (22,989 ) 2,762 (142 ) 1,150,074 (23,131 ) CLO and other ABS 427,307 (1,813 ) 774 (4 ) 428,081 (1,817 ) CMBS 378,523 (6,009 ) — — 378,523 (6,009 ) RMBS 739,217 (11,962 ) 10,895 (380 ) 750,112 (12,342 ) Total AFS securities $ 3,070,757 (47,981 ) 17,853 (652 ) 3,088,610 (48,633 ) December 31, 2017 Less than 12 months 12 months or longer Total ($ in thousands) Fair Value Unrealized Losses 1 Fair Value Unrealized Losses 1 Fair Value Unrealized 1 AFS fixed income securities: U.S. government and government agencies $ 23,516 (233 ) 250 — 23,766 (233 ) Foreign government 1,481 (11 ) — — 1,481 (11 ) Obligations of states and political subdivisions 107,514 (422 ) 14,139 (160 ) 121,653 (582 ) Corporate securities 238,326 (1,744 ) 3,228 (18 ) 241,554 (1,762 ) CLO and other ABS 74,977 (196 ) 1,655 (6 ) 76,632 (202 ) CMBS 154,267 (773 ) 5,214 (68 ) 159,481 (841 ) RMBS 269,485 (1,285 ) 11,200 (145 ) 280,685 (1,430 ) Total AFS fixed income securities 869,566 (4,664 ) 35,686 (397 ) 905,252 (5,061 ) AFS equity securities: Common stock 4,727 (226 ) — — 4,727 (226 ) Preferred stock 3,833 (71 ) — — 3,833 (71 ) Total AFS equity securities 8,560 (297 ) — — 8,560 (297 ) Total AFS $ 878,126 (4,961 ) 35,686 (397 ) 913,812 (5,358 ) 1 Gross unrealized losses include non-OTTI unrealized amounts and OTTI losses recognized in AOCI.
Schedule of Fixed Maturity Securities By Contractual Maturities	AFS HTM ($ in thousands) Fair Value Carrying Value Fair Value Due in one year or less $ 186,138 8,309 8,383 Due after one year through five years 2,034,623 27,160 28,544 Due after five years through 10 years 2,733,420 6,547 6,446 Due after 10 years 183,472 — — Total fixed income securities $ 5,137,653 42,016 43,373
Schedule of Other Investment Portfolio By Strategy And Remaining Commitment Amount and Maximum Exposure to Loss Associated With Each Strategy	Other Investments June 30, 2018 December 31, 2017 ($ in thousands) Carrying Value Remaining Commitment Maximum Exposure to Loss 1 Carrying Value Remaining Commitment Maximum Exposure to Loss 1 Alternative Investments Private equity $ 59,681 110,833 170,514 52,251 99,026 151,277 Private credit 40,916 89,757 130,673 37,743 94,959 132,702 Real assets 23,430 36,588 60,018 25,379 27,014 52,393 Total alternative investments 124,027 237,178 361,205 115,373 220,999 336,372 Other securities 21,176 — 21,176 16,895 — 16,895 Total other investments $ 145,203 237,178 382,381 132,268 220,999 353,267 1 The maximum exposure to loss includes both the carry value of these investments and the related unfunded 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 June 30, Six Months ended June 30, ($ in millions) 2018 2017 2018 2017 Net investment loss $ (6.4 ) (88.0 ) (41.8 ) (62.4 ) Realized gains (losses) 629.5 (69.2 ) 1,223.5 (304.3 ) Net change in unrealized (depreciation) appreciation (1,200.2 ) 1,328.5 (738.6 ) 1,890.0 Net (loss) gain $ (577.1 ) 1,171.3 443.1 1,523.3 Selective’s insurance subsidiaries’ alternative investments gain $ 1.9 5.2 3.5 6.8
Schedule of Securities Pledged As Collateral	($ in millions) FHLBI Collateral FHLBNY Collateral State and Regulatory Deposits Total U.S. government and government agencies $ — — 22.3 22.3 Obligations of states and political subdivisions — — 3.1 3.1 CMBS 7.2 9.6 — 16.8 RMBS 58.2 79.8 — 138.0 Total pledged as collateral $ 65.4 89.4 25.4 180.2
Schedule of Pre-Tax Net Investment Income Earned	Quarter ended June 30, Six Months ended June 30, ($ in thousands) 2018 2017 2018 2017 Fixed income securities $ 43,774 37,668 $ 85,815 74,559 Equity securities 1,820 1,419 3,797 2,887 Short-term investments 611 377 1,134 627 Other investments 2,094 5,231 3,657 6,834 Investment expenses (2,746 ) (3,265 ) (5,619 ) (6,058 ) Net investment income earned $ 45,553 41,430 $ 88,784 78,849
Schedule of Components of Net Realized and Unrealized Gains and Losses Excluding OTTI Charges	Quarter ended June 30, Six Months ended June 30, ($ in thousands) 2018 2017 2018 2017 Net realized (losses) gains on the disposals of securities: Fixed income securities $ (1,174 ) 2,606 (4,509 ) 4,570 Equity securities 1,226 350 9,295 350 Short-term investments 2 — (1 ) — Other investments — (5 ) — 461 Net realized gains on the disposal of securities 54 2,951 4,785 5,381 OTTI charges (2,821 ) (1,217 ) (4,033 ) (4,692 ) Net realized (losses) gains (2,767 ) 1,734 752 689 Unrealized gains (losses) recognized in income on equity securities 1 1,115 — (12,953 ) — Total net realized and unrealized investment (losses) gains $ (1,652 ) 1,734 $ (12,201 ) 689 1 Includes unrealized holding gains (losses) of: (i) $2.3 million in Second Quarter 2018 and $(2.7) million in Six Months 2018 on equity securities remaining in our portfolio as of June 30, 2018 ; and (ii) $(1.2) million in Second Quarter 2018 and $(10.3) million in Six Months 2018 on equity securities sold during the period.
Schedule of Realized Gains and Losses on Disposals of Securities	Quarter ended June 30, Six Months ended June 30, ($ in thousands) 2018 2017 2018 2017 HTM fixed income securities Gains $ — 44 2 44 Losses — — — (1 ) AFS fixed income securities Gains 1,971 2,715 4,594 6,267 Losses (3,145 ) (153 ) (9,105 ) (1,740 ) Equity securities Gains 1,226 350 9,625 350 Losses — — (330 ) — Short-term investments Gains 2 — 3 2 Losses — — (4 ) (2 ) Other investments Gains — — — 480 Losses — (5 ) — (19 ) Total net realized gains on disposals of securities $ 54 2,951 4,785 5,381

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Schedule of Quantitative Disclosures of Our Financial Assets That Were Measured At Fair Value	June 30, 2018 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 Inputs (Level 3) Description Measured on a recurring basis: AFS fixed income securities: U.S. government and government agencies $ 38,896 22,479 16,417 — Foreign government 17,982 — 17,982 — Obligations of states and political subdivisions 1,253,667 — 1,253,667 — Corporate securities 1,614,484 — 1,614,484 — CLO and other ABS 771,597 — 768,408 3,189 CMBS 451,593 — 451,593 — RMBS 989,434 — 989,434 — Total AFS fixed income securities 5,137,653 22,479 5,111,985 3,189 Equity securities: Common stock 2 172,157 145,038 — — Preferred stock 4,421 4,421 — — Total equity securities 176,578 149,459 — — Short-term investments 164,118 163,120 998 — Total assets measured at fair value $ 5,478,349 335,058 5,112,983 3,189 December 31, 2017 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 Inputs (Level 3) Description Measured on a recurring basis: AFS fixed income securities: U.S. government and government agencies $ 49,740 24,652 25,088 — Foreign government 18,555 — 18,555 — Obligations of states and political subdivisions 1,582,970 — 1,582,970 — Corporate securities 1,617,468 — 1,617,468 — CLO and other ABS 795,458 — 795,458 — CMBS 383,449 — 376,895 6,554 RMBS 714,882 — 714,882 — Total AFS fixed income securities 5,162,522 24,652 5,131,316 6,554 AFS equity securities: Common stock 2 167,757 138,640 — 5,398 Preferred stock 14,948 14,948 — — Total AFS equity securities 182,705 153,588 — 5,398 Total AFS securities 5,345,227 178,240 5,131,316 11,952 Short-term investments 165,555 165,555 — — Total assets measured at fair value $ 5,510,782 343,795 5,131,316 11,952 1 There were no transfers of securities between Level 1 and Level 2. 2 Investments amounting to $27.1 million at June 30, 2018 , and $23.7 million at December 31, 2017 , were measured at fair value using net asset value per share (or its practical expedient) and have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to total assets measured at fair value
Schedule of Changes in Fair Value of Securities Using Level 3 Inputs	June 30, 2018 ($ in thousands) CMBS Common Stock CLO and Other ABS Fair value, December 31, 2017 $ 6,554 5,398 — Total net (losses) gains for the period included in: Other comprehensive income ("OCI") — — — Net income — — — Purchases — — 3,189 Sales — — — Issuances — — — Settlements — — — Transfers into Level 3 — — — Transfers out of Level 3 (6,554 ) (5,398 ) — Fair value, June 30, 2018 $ — — 3,189
Schedule of Quantitative Information of Our Financial Assets and Liabilities That Were Disclosed at Fair Value	June 30, 2018 Fair Value Measurements Using ($ in thousands) Assets/ Quoted Prices in Active Markets for Identical Assets/ Liabilities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Financial Assets HTM: Obligations of states and political subdivisions $ 23,260 — 23,260 — Corporate securities 20,113 — 11,628 8,485 Total HTM fixed income securities $ 43,373 — 34,888 8,485 Financial Liabilities Long-term debt: 7.25% Senior Notes $ 57,231 — 57,231 — 6.70% Senior Notes 108,453 — 108,453 — 5.875% Senior Notes 186,924 186,924 — — 1.61% borrowings from FHLBNY 23,979 — 23,979 — 1.56% borrowings from FHLBNY 23,915 — 23,915 — 3.03% borrowings from FHLBI 58,483 — 58,483 — Total long-term debt $ 458,985 186,924 272,061 — December 31, 2017 Fair Value Measurements Using ($ in thousands) Assets/ Quoted Prices in Active Markets for Identical Assets/ Liabilities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Financial Assets HTM: Obligations of states and political subdivisions $ 26,261 — 26,261 — Corporate securities 17,839 — 12,306 5,533 Total HTM fixed income securities $ 44,100 — 38,567 5,533 Financial Liabilities Long-term debt: 7.25% Senior Notes $ 61,391 — 61,391 — 6.70% Senior Notes 116,597 — 116,597 — 5.875% Senior Notes 186,332 186,332 — — 1.61% borrowings from FHLBNY 24,270 — 24,270 — 1.56% borrowings from FHLBNY 24,210 — 24,210 — 3.03% borrowings from FHLBI 60,334 — 60,334 — Total long-term debt $ 473,134 186,332 286,802 —

Reinsurance (Tables)

Reinsurance (Tables)	6 Months Ended
	Jun. 30, 2018
Reinsurance Disclosures [Abstract]
Schedule of List Of Direct, Assumed, And Ceded Reinsurance Amounts	Quarter ended June 30, Six Months ended June 30, ($ in thousands) 2018 2017 2018 2017 Premiums written: Direct $ 753,363 706,408 $ 1,467,597 1,390,228 Assumed 6,536 6,488 12,807 12,179 Ceded (104,651 ) (99,082 ) (200,596 ) (189,889 ) Net $ 655,248 613,814 $ 1,279,808 1,212,518 Premiums earned: Direct $ 696,723 654,588 $ 1,380,456 1,301,316 Assumed 6,612 6,063 12,736 11,842 Ceded (98,499 ) (92,621 ) (196,528 ) (184,274 ) Net $ 604,836 568,030 $ 1,196,664 1,128,884 Loss and loss expenses incurred: Direct $ 391,014 389,550 $ 811,930 731,672 Assumed 2,364 7,766 10,368 12,203 Ceded (27,050 ) (55,757 ) (71,029 ) (84,844 ) Net $ 366,328 341,559 $ 751,269 659,031
Schedule of Ceded Premiums and Losses Related to Flood Operations	Ceded premiums and losses related to our participation in the NFIP, under which 100% of our flood premiums, losses, and loss expenses are ceded to the NFIP, are as follows: Ceded to NFIP Quarter ended June 30, Six Months ended June 30, ($ in thousands) 2018 2017 2018 2017 Ceded premiums written $ (66,341 ) (63,808 ) $ (123,010 ) (120,142 ) Ceded premiums earned (60,143 ) (57,655 ) (119,134 ) (114,932 ) Ceded loss and loss expenses incurred (10,261 ) (15,140 ) (25,980 ) (21,681 )

Reserve for Loss and Loss Exp27

Reserve for Loss and Loss Expense (Tables)	6 Months Ended
	Jun. 30, 2018
Insurance Loss Reserves [Abstract]
Schedule of Liability for Unpaid Claims and Claims Adjustment Expense	Six Months ended June 30, ($ in thousands) 2018 2017 Gross reserve for loss and loss expense, at beginning of year $ 3,771,240 3,691,719 Less: reinsurance recoverable on unpaid loss and loss expense, at beginning of year 585,855 611,200 Net reserve for loss and loss expense, at beginning of year 3,185,385 3,080,519 Incurred loss and loss expense for claims occurring in the: Current year 756,855 684,877 Prior years (5,586 ) (25,846 ) Total incurred loss and loss expense 751,269 659,031 Paid loss and loss expense for claims occurring in the: Current year 214,169 171,724 Prior years 457,441 425,521 Total paid loss and loss expense 671,610 597,245 Net reserve for loss and loss expense, at end of period 3,265,044 3,142,305 Add: Reinsurance recoverable on unpaid loss and loss expense, at end of period 539,321 588,916 Gross reserve for loss and loss expense at end of period $ 3,804,365 3,731,221

Segment Information (Tables)

Segment Information (Tables)	6 Months Ended
	Jun. 30, 2018
Segment Reporting [Abstract]
Schedule of Revenue By Segment	Revenue by Segment Quarter ended June 30, Six Months ended June 30, ($ in thousands) 2018 2017 2018 2017 Standard Commercial Lines: Net premiums earned: Commercial automobile $ 122,104 108,316 240,335 215,445 Workers compensation 80,021 79,460 158,844 158,786 General liability 153,002 141,503 302,831 281,487 Commercial property 82,162 78,052 162,488 154,443 Businessowners’ policies 25,829 24,989 51,420 49,834 Bonds 8,335 6,986 16,469 13,484 Other 4,559 4,288 8,989 8,529 Miscellaneous income 2,882 3,016 4,708 5,876 Total Standard Commercial Lines revenue 478,894 446,610 946,084 887,884 Standard Personal Lines: Net premiums earned: Personal automobile 41,810 37,663 82,252 74,613 Homeowners 32,223 32,467 64,424 65,167 Other 1,644 1,542 3,257 3,093 Miscellaneous income 297 275 649 656 Total Standard Personal Lines revenue 75,974 71,947 150,582 143,529 E&S Lines: Net premiums earned: Casualty lines 39,379 39,054 77,919 76,966 Property lines 13,768 13,710 27,436 27,037 Miscellaneous income — — 1 — Total E&S Lines revenue 53,147 52,764 105,356 104,003 Investments: Net investment income 45,553 41,430 88,784 78,849 Net realized and unrealized investment (losses) gains (1,652 ) 1,734 (12,201 ) 689 Total Investments revenue 43,901 43,164 76,583 79,538 Total revenues $ 651,916 614,485 1,278,605 1,214,954
Schedule of Income Before and After Federal Income Tax	Income Before and After Federal Income Tax Quarter ended June 30, Six Months ended June 30, ($ in thousands) 2018 2017 2018 2017 Standard Commercial Lines: Underwriting gain, before federal income tax $ 41,016 34,759 47,820 77,305 Underwriting gain, after federal income tax 32,403 22,593 37,778 50,248 Combined ratio 91.4 % 92.2 94.9 91.2 Standard Personal Lines: Underwriting gain (loss), before federal income tax $ 4,805 (5,768 ) 3,299 (662 ) Underwriting gain (loss), after federal income tax 3,796 (3,749 ) 2,606 (430 ) Combined ratio 93.7 % 108.0 97.8 100.5 E&S Lines: Underwriting (loss) gain, before federal income tax $ (7,789 ) 1,319 (8,354 ) 2,889 Underwriting (loss) gain, after federal income tax (6,154 ) 857 (6,600 ) 1,878 Combined ratio 114.7 % 97.5 107.9 97.2 Investments: Net investment income $ 45,553 41,430 88,784 78,849 Net realized and unrealized investment (losses) gains (1,652 ) 1,734 (12,201 ) 689 Total investment income, before federal income tax 43,901 43,164 76,583 79,538 Tax on investment income 7,617 11,734 12,843 21,336 Total investment income, after federal income tax $ 36,284 31,430 63,740 58,202
Schedule of Reconciliation of Segment Results to Income Before Federal Income Tax	Reconciliation of Segment Results to Income Before Federal Income Tax Quarter ended June 30, Six Months ended June 30, ($ in thousands) 2018 2017 2018 2017 Underwriting gain (loss) Standard Commercial Lines $ 41,016 34,759 47,820 77,305 Standard Personal Lines 4,805 (5,768 ) 3,299 (662 ) E&S Lines (7,789 ) 1,319 (8,354 ) 2,889 Investment income 43,901 43,164 76,583 79,538 Total all segments 81,933 73,474 119,348 159,070 Interest expense (6,125 ) (6,081 ) (12,277 ) (12,187 ) Corporate expenses (3,283 ) (8,464 ) (14,615 ) (20,380 ) Income, before federal income tax $ 72,525 58,929 92,456 126,503

Retirement Plans (Table)

Retirement Plans (Table)	6 Months Ended
	Jun. 30, 2018
Retirement Benefits [Abstract]
Schedule of Components of Net Periodic Benefit Cost	Pension Plan Pension Plan Quarter ended June 30, Six Months ended June 30, ($ in thousands) 2018 2017 2018 2017 Net Periodic Benefit Cost: Interest cost $ 3,095 3,110 6,190 6,221 Expected return on plan assets (5,681 ) (4,855 ) (11,363 ) (9,709 ) Amortization of unrecognized net actuarial loss 493 482 987 963 Total net periodic benefit cost 1 $ (2,093 ) (1,263 ) (4,186 ) (2,525 ) 1 The components of net periodic benefit cost 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 Six Months ended June 30, 2018 2017 Weighted-Average Expense Assumptions: Discount rate 3.78 % 4.41 % Effective interest rate for calculation of interest cost 3.46 3.84 Expected return on plan assets 6.36 6.24

Comprehensive Income (Tables)

Comprehensive Income (Tables)	6 Months Ended
	Jun. 30, 2018
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Schedule of Components of Comprehensive Income-Gross and Net of Tax	Second Quarter 2018 ($ in thousands) Gross Tax Net Net income $ 72,525 13,706 58,819 Components of other comprehensive loss: Unrealized losses on investment securities : Unrealized holding losses during period (23,993 ) (5,038 ) (18,955 ) Amounts reclassified into net income: HTM securities (8 ) (2 ) (6 ) Realized losses on disposals of AFS securities 2,870 603 2,267 Total unrealized losses on investment securities (21,131 ) (4,437 ) (16,694 ) Defined benefit pension and post-retirement plans: Amounts reclassified into net income: Net actuarial loss 531 111 420 Total defined benefit pension and post-retirement plans 531 111 420 Other comprehensive loss (20,600 ) (4,326 ) (16,274 ) Comprehensive income $ 51,925 9,380 42,545 Second Quarter 2017 ($ in thousands) Gross Tax Net Net income $ 58,929 17,503 41,426 Components of OCI: Unrealized gains on investment securities : Unrealized holding gains during period 35,887 12,561 23,326 Non-credit portion of OTTI recognized in OCI 6 2 4 Amounts reclassified into net income: HTM securities (43 ) (15 ) (28 ) Realized gains on disposals of AFS securities (1,885 ) (660 ) (1,225 ) Total unrealized gains on investment securities 33,965 11,888 22,077 Defined benefit pension and post-retirement plans: Amounts reclassified into net income: Net actuarial loss 508 178 330 Total defined benefit pension and post-retirement plans 508 178 330 Other comprehensive income 34,473 12,066 22,407 Comprehensive income $ 93,402 29,569 63,833 Six Months 2018 ($ in thousands) Gross Tax Net Net income $ 92,456 14,712 77,744 Components of other comprehensive loss: Unrealized losses on investment securities : Unrealized holding losses during period (109,308 ) (22,955 ) (86,353 ) Amounts reclassified into net income: HTM securities (20 ) (4 ) (16 ) Realized losses on disposals of AFS securities 7,419 1,558 5,861 Total unrealized losses on investment securities (101,909 ) (21,401 ) (80,508 ) Defined benefit pension and post-retirement plans: Amounts reclassified into net income: Net actuarial loss 1,063 223 840 Total defined benefit pension and post-retirement plans 1,063 223 840 Other comprehensive loss (100,846 ) (21,178 ) (79,668 ) Comprehensive loss $ (8,390 ) (6,466 ) (1,924 ) Six Months 2017 ($ in thousands) Gross Tax Net Net income $ 126,503 34,637 91,866 Components of OCI: Unrealized gains on investment securities : Unrealized holding gains during period 61,672 21,585 40,087 Non-credit portion of OTTI recognized in OCI 6 2 4 Amounts reclassified into net income: HTM securities (92 ) (32 ) (60 ) Realized gains on disposals of AFS securities (375 ) (131 ) (244 ) Total unrealized gains on investment securities 61,211 21,424 39,787 Defined benefit pension and post-retirement plans: Amounts reclassified into net income: Net actuarial loss 1,015 355 660 Total defined benefit pension and post-retirement plans 1,015 355 660 Other comprehensive income 62,226 21,779 40,447 Comprehensive income $ 188,729 56,416 132,313
Schedule of Components of Accumulated Other Comprehensive Income Net of Tax	June 30, 2018 Defined Benefit Pension and Post-Retirement Plans Net Unrealized Gains (Losses) on Investment Securities Total AOCI ($ in thousands) OTTI Related HTM Related All Other Investments Subtotal Balance, December 31, 2017 $ (59 ) (14 ) 80,648 80,575 (60,405 ) 20,170 Cumulative effect adjustments (12 ) (2 ) (12,792 ) (12,806 ) (12,213 ) (25,019 ) Balance, December 31, 2017 as adjusted (71 ) (16 ) 67,856 67,769 (72,618 ) (4,849 ) OCI before reclassifications — — (86,353 ) (86,353 ) — (86,353 ) Amounts reclassified from AOCI — (16 ) 5,861 5,845 840 6,685 Net current period OCI — (16 ) (80,492 ) (80,508 ) 840 (79,668 ) Balance, June 30, 2018 $ (71 ) (32 ) (12,636 ) (12,739 ) (71,778 ) (84,517 )
Schedule of Reclassifications Out Of Accumulated Other Comprehensive Income	Quarter ended June 30, Six Months ended June 30, Affected Line Item in the Unaudited Consolidated Statements of Income ($ in thousands) 2018 2017 2018 2017 HTM related Unrealized losses on HTM disposals $ (7 ) 17 (6 ) 30 Net realized and unrealized (losses) gains Amortization of net unrealized gains on HTM securities (1 ) (60 ) (14 ) (122 ) Net investment income earned (8 ) (43 ) (20 ) (92 ) Income before federal income tax 2 15 4 32 Total federal income tax expense (6 ) (28 ) (16 ) (60 ) Net income Realized losses (gains) on AFS and OTTI Realized losses (gains) on AFS disposals and OTTI 2,870 (1,885 ) 7,419 (375 ) Net realized and unrealized (losses) gains 2,870 (1,885 ) 7,419 (375 ) Income before federal income tax (603 ) 660 (1,558 ) 131 Total federal income tax expense 2,267 (1,225 ) 5,861 (244 ) Net income Defined benefit pension and post-retirement life plans Net actuarial loss 113 111 225 221 Loss and loss expense incurred 418 397 838 794 Other insurance expenses Total defined benefit pension and post-retirement life 531 508 1,063 1,015 Income before federal income tax (111 ) (178 ) (223 ) (355 ) Total federal income tax expense 420 330 840 660 Net income Total reclassifications for the period $ 2,681 (923 ) 6,685 356 Net income

Federal Income Taxes (Tables)

Federal Income Taxes (Tables)	6 Months Ended
	Jun. 30, 2018
Income Tax Disclosure [Abstract]
Schedule of Effective Income Tax Rate Reconciliation	Quarter ended June 30, Six Months ended June 30, ($ in thousands) 2018 2017 2018 2017 Statutory tax rate 21 % 35 21 35 Tax at statutory rate $ 15,231 20,625 19,416 44,276 Tax-advantaged interest (1,393 ) (2,757 ) (2,904 ) (5,564 ) Dividends received deduction (210 ) (625 ) (336 ) (956 ) Stock-based compensation (82 ) (374 ) (2,548 ) (3,323 ) Other 160 634 1,084 204 Federal income tax expense $ 13,706 17,503 14,712 34,637

Accounting Pronouncements (Deta

Accounting Pronouncements (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Undistributed gains of equity method investments	$ (1,628)	$ (3,584)
Distributions in excess of current year income of equity method investments	1,450	552
Decrease (increase) in other assets	(6,550)	(3,862)
Net cash provided by operating activities	92,257	95,451
Distributions from other investments	15,927	9,300
Net cash used in investing activities	(96,402)	(94,017)
Scenario, Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Undistributed gains of equity method investments		(3,575)
Distributions in excess of current year income of equity method investments		0
Decrease (increase) in other assets		24,953
Net cash provided by operating activities		123,723
Distributions from other investments		9,843
Net cash used in investing activities		(93,474)
AOCI Attributable to Parent [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption	(25,019)
AOCI Attributable to Parent [Member] | Accounting Standards Update 2016-01 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption	(30,726)	0
AOCI Attributable to Parent [Member] | Accounting Standards Update 2018-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption	$ 5,707	$ 0

Statements of Cash Flow (Cash F

Statements of Cash Flow (Cash Flow Supplemental Disclosures) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Interest	$ 12,064	$ 11,963
Federal income tax	4,193	27,000
Non-cash acquisition of fixed income securities, AFS	32	0
Assets acquired under capital lease arrangements	0	278
Non-cash purchase of property and equipment	18	0
Cash	4,876		$ 534
Restricted cash	11,604		44,176
Total cash and restricted cash shown in the Statements of Cash Flows	16,480	16,760	$ 44,710	$ 37,405
AFS Fixed Maturity Securities [Member]
Exchange of fixed income securities, AFS	$ 32,101	$ 1,029

Investments (Held-To-Maturity S

Investments (Held-To-Maturity Securities Disclosure) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 42,057	$ 42,150
Net Unrealized Gains (Losses)	(41)	(21)
HTM, Carrying Value	42,016	42,129
Unrecognized Holding Gains	1,482	2,026
Unrecognized Holding Losses	(125)	(55)
Held-to-maturity securities, fair value	43,373	44,100
Obligations of States and Political Subdivisions [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	22,490	25,154
Net Unrealized Gains (Losses)	49	84
HTM, Carrying Value	22,539	25,238
Unrecognized Holding Gains	721	1,023
Unrecognized Holding Losses	0	0
Held-to-maturity securities, fair value	23,260	26,261
Corporate Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	19,567	16,996
Net Unrealized Gains (Losses)	(90)	(105)
HTM, Carrying Value	19,477	16,891
Unrecognized Holding Gains	761	1,003
Unrecognized Holding Losses	(125)	(55)
Held-to-maturity securities, fair value	$ 20,113	$ 17,839

Investments (Available-For-Sale

Investments (Available-For-Sale Securities Disclosure) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	$ 5,153,737	$ 5,220,527
Unrealized Gains	32,549	130,058
Unrealized Losses	(48,633)	(5,358)
AFS securities, fair value	5,137,653	5,345,227
AFS Fixed Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost		5,076,716
Unrealized Gains		90,867
Unrealized Losses		(5,061)
AFS securities, fair value		5,162,522
AFS Fixed Income Securities [Member] | U.S. Government and Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	39,368	49,326
Unrealized Gains	291	647
Unrealized Losses	(763)	(233)
AFS securities, fair value	38,896	49,740
AFS Fixed Income Securities [Member] | Foreign Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	18,024	18,040
Unrealized Gains	87	526
Unrealized Losses	(129)	(11)
AFS securities, fair value	17,982	18,555
AFS Fixed Income Securities [Member] | Obligations of States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	1,240,487	1,539,307
Unrealized Gains	17,622	44,245
Unrealized Losses	(4,442)	(582)
AFS securities, fair value	1,253,667	1,582,970
AFS Fixed Income Securities [Member] | Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	1,630,998	1,588,339
Unrealized Gains	6,617	30,891
Unrealized Losses	(23,131)	(1,762)
AFS securities, fair value	1,614,484	1,617,468
AFS Fixed Income Securities [Member] | Collateralized Loan Obligations and Other Asset Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	768,466	789,152
Unrealized Gains	4,948	6,508
Unrealized Losses	(1,817)	(202)
AFS securities, fair value	771,597	795,458
AFS Fixed Income Securities [Member] | Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	457,344	382,727
Unrealized Gains	258	1,563
Unrealized Losses	(6,009)	(841)
AFS securities, fair value	451,593	383,449
AFS Fixed Income Securities [Member] | Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	999,050	709,825
Unrealized Gains	2,726	6,487
Unrealized Losses	(12,342)	(1,430)
AFS securities, fair value	$ 989,434	714,882
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost		143,811
Unrealized Gains		39,191
Unrealized Losses		(297)
AFS securities, fair value		182,705
Equity Securities [Member] | Common Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost		129,696
Unrealized Gains		38,287
Unrealized Losses		(226)
AFS securities, fair value		167,757
Equity Securities [Member] | Preferred Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost		14,115
Unrealized Gains		904
Unrealized Losses		(71)
AFS securities, fair value		$ 14,948

Investments (Fair Value and Gro

Investments (Fair Value and Gross Pre-Tax Net Unrealized Unrecognized Loss of Securities By Length of Time) (Details) - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 31, 2017
Percent Of Securities of Amortized Cost In An Unrealized Unrecognized Loss Position		1.00%	1.00%
AFS Fair Value, Less than 12 months		$ 3,070,757	$ 878,126
AFS Unrealized Losses, Less than 12 months	[1]	(47,981)	(4,961)
AFS Fair Value, 12 months or longer		17,853	35,686
AFS Unrealized Losses, 12 months or longer	[1]	(652)	(397)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		3,088,610	913,812
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	[1]	(48,633)	(5,358)
Held-to-maturity Securities [Member]
Unrealized Unrecognized Loss		300	100
AFS Fixed Income Securities [Member]
AFS Fair Value, Less than 12 months			869,566
AFS Unrealized Losses, Less than 12 months	[1]		(4,664)
AFS Fair Value, 12 months or longer			35,686
AFS Unrealized Losses, 12 months or longer	[1]		(397)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value			905,252
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	[1]		(5,061)
AFS Fixed Income Securities [Member] | U.S. Government and Government Agencies [Member]
AFS Fair Value, Less than 12 months		28,005	23,516
AFS Unrealized Losses, Less than 12 months	[1]	(763)	(233)
AFS Fair Value, 12 months or longer		0	250
AFS Unrealized Losses, 12 months or longer	[1]	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		28,005	23,766
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	[1]	(763)	(233)
AFS Fixed Income Securities [Member] | Foreign Government [Member]
AFS Fair Value, Less than 12 months		7,740	1,481
AFS Unrealized Losses, Less than 12 months	[1]	(129)	(11)
AFS Fair Value, 12 months or longer		0	0
AFS Unrealized Losses, 12 months or longer	[1]	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		7,740	1,481
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	[1]	(129)	(11)
AFS Fixed Income Securities [Member] | Obligations of States and Political Subdivisions [Member]
AFS Fair Value, Less than 12 months		342,653	107,514
AFS Unrealized Losses, Less than 12 months	[1]	(4,316)	(422)
AFS Fair Value, 12 months or longer		3,422	14,139
AFS Unrealized Losses, 12 months or longer	[1]	(126)	(160)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		346,075	121,653
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	[1]	(4,442)	(582)
AFS Fixed Income Securities [Member] | Corporate Securities [Member]
AFS Fair Value, Less than 12 months		1,147,312	238,326
AFS Unrealized Losses, Less than 12 months	[1]	(22,989)	(1,744)
AFS Fair Value, 12 months or longer		2,762	3,228
AFS Unrealized Losses, 12 months or longer	[1]	(142)	(18)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		1,150,074	241,554
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	[1]	(23,131)	(1,762)
AFS Fixed Income Securities [Member] | Collateralized Loan Obligations and Other Asset Backed Securities [Member]
AFS Fair Value, Less than 12 months		427,307	74,977
AFS Unrealized Losses, Less than 12 months	[1]	(1,813)	(196)
AFS Fair Value, 12 months or longer		774	1,655
AFS Unrealized Losses, 12 months or longer	[1]	(4)	(6)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		428,081	76,632
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	[1]	(1,817)	(202)
AFS Fixed Income Securities [Member] | Commercial Mortgage Backed Securities [Member]
AFS Fair Value, Less than 12 months		378,523	154,267
AFS Unrealized Losses, Less than 12 months	[1]	(6,009)	(773)
AFS Fair Value, 12 months or longer		0	5,214
AFS Unrealized Losses, 12 months or longer	[1]	0	(68)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		378,523	159,481
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	[1]	(6,009)	(841)
AFS Fixed Income Securities [Member] | Residential Mortgage Backed Securities [Member]
AFS Fair Value, Less than 12 months		739,217	269,485
AFS Unrealized Losses, Less than 12 months	[1]	(11,962)	(1,285)
AFS Fair Value, 12 months or longer		10,895	11,200
AFS Unrealized Losses, 12 months or longer	[1]	(380)	(145)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		750,112	280,685
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	[1]	$ (12,342)	(1,430)
Equity Securities [Member]
AFS Fair Value, Less than 12 months			8,560
AFS Unrealized Losses, Less than 12 months	[1]		(297)
AFS Fair Value, 12 months or longer			0
AFS Unrealized Losses, 12 months or longer	[1]		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value			8,560
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	[1]		(297)
Equity Securities [Member] | Common Stock [Member]
AFS Fair Value, Less than 12 months			4,727
AFS Unrealized Losses, Less than 12 months	[1]		(226)
AFS Fair Value, 12 months or longer			0
AFS Unrealized Losses, 12 months or longer	[1]		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value			4,727
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	[1]		(226)
Equity Securities [Member] | Preferred Stock [Member]
AFS Fair Value, Less than 12 months			3,833
AFS Unrealized Losses, Less than 12 months	[1]		(71)
AFS Fair Value, 12 months or longer			0
AFS Unrealized Losses, 12 months or longer	[1]		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value			3,833
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	[1]		$ (71)
[1]	Gross unrealized losses include non-OTTI unrealized amounts and OTTI losses recognized in AOCI.

Investments (Fixed Income Secur

Investments (Fixed Income Securities by Contractual Maturity) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Schedule of Fixed Income Securities [Line Items]
Due in one year or less fair value, AFS	$ 186,138
Due after one year through five years fair value, AFS	2,034,623
Due after five years through 10 years fair value, AFS	2,733,420
Due after 10 years fair value, AFS	183,472
AFS, Fair Value	5,137,653	$ 5,162,522
Due in one year or less carrying value, HTM	8,309
Due after one year through five years carrying value, HTM	27,160
Due after five years through 10 years carrying value, HTM	6,547
Due after 10 years carrying value, HTM	0
HTM, Carrying Value	42,016	42,129
Due in one year or less fair value, HTM	8,383
Due after one year through five years fair value, HTM	28,544
Due after five years through 10 years fair value, HTM	6,446
Due after 10 years fair value, HTM	0
HTM, Fair Value	$ 43,373	$ 44,100

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		Jun. 30, 2018	Dec. 31, 2017
Carrying Value		$ 145,203	$ 132,268
Other Investments [Member]
Carrying Value		145,203	132,268
Remaining Commitment		237,178	220,999
Maximum Exposure to Loss	[1]	382,381	353,267
Alternative Investments [Member]
Carrying Value		124,027	115,373
Remaining Commitment		237,178	220,999
Maximum Exposure to Loss	[1]	361,205	336,372
Private Equity [Member] | Alternative Investments [Member]
Carrying Value		59,681	52,251
Remaining Commitment		110,833	99,026
Maximum Exposure to Loss	[1]	170,514	151,277
Private Credit [Member] | Alternative Investments [Member]
Carrying Value		40,916	37,743
Remaining Commitment		89,757	94,959
Maximum Exposure to Loss	[1]	130,673	132,702
Real Assets [Member] | Alternative Investments [Member]
Carrying Value		23,430	25,379
Remaining Commitment		36,588	27,014
Maximum Exposure to Loss	[1]	60,018	52,393
Other Securities [Member]
Carrying Value		21,176	16,895
Remaining Commitment		0	0
Maximum Exposure to Loss	[1]	$ 21,176	$ 16,895
[1]	The maximum exposure to loss includes both the carry value of these investments and the related unfunded 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		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Schedule of Equity Method Investments [Line Items]
Net investment income earned	$ 45,553	$ 41,430	$ 88,784	$ 78,849
Alternative Investments [Member]
Schedule of Equity Method Investments [Line Items]
Net investment income earned	1,900	5,200	3,500	6,800
Investments accounted for under the equity method [Member]
Schedule of Equity Method Investments [Line Items]
Net investment loss	(6,400)	(88,000)	(41,800)	(62,400)
Realized gains (losses)	629,500	(69,200)	1,223,500	(304,300)
Net change in unrealized (depreciation) appreciation	(1,200,200)	1,328,500	(738,600)	1,890,000
Net (loss) gain	$ (577,100)	$ 1,171,300	$ 443,100	$ 1,523,300

Investments (Investments Pledge

Investments (Investments Pledged as Collateral) (Details) $ in Millions	Jun. 30, 2018USD ($)
Financial Instruments Owned and Pledged as Collateral [Line Items]
Carrying Value Bonds On Deposit With Various State And Regulatory Agencies	$ 25.4
Securities Pledged As Collateral	180.2
U.S. Government and Government Agencies [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Carrying Value Bonds On Deposit With Various State And Regulatory Agencies	22.3
Securities Pledged As Collateral	22.3
Obligations of States and Political Subdivisions [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Carrying Value Bonds On Deposit With Various State And Regulatory Agencies	3.1
Securities Pledged As Collateral	3.1
Commercial Mortgage Backed Securities [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Carrying Value Bonds On Deposit With Various State And Regulatory Agencies	0
Securities Pledged As Collateral	16.8
Residential Mortgage Backed Securities [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Carrying Value Bonds On Deposit With Various State And Regulatory Agencies	0
Securities Pledged As Collateral	138
Federal Home Loan Bank of Indianapolis [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Fixed Income Securities Pledged For FHLB Collateral	65.4
Federal Home Loan Bank of Indianapolis [Member] | U.S. Government and Government Agencies [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Fixed Income Securities Pledged For FHLB Collateral	0
Federal Home Loan Bank of Indianapolis [Member] | Obligations of States and Political Subdivisions [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Fixed Income Securities Pledged For FHLB Collateral	0
Federal Home Loan Bank of Indianapolis [Member] | Commercial Mortgage Backed Securities [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Fixed Income Securities Pledged For FHLB Collateral	7.2
Federal Home Loan Bank of Indianapolis [Member] | Residential Mortgage Backed Securities [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Fixed Income Securities Pledged For FHLB Collateral	58.2
Federal Home Loan Bank of New York [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Fixed Income Securities Pledged For FHLB Collateral	89.4
Federal Home Loan Bank of New York [Member] | U.S. Government and Government Agencies [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Fixed Income Securities Pledged For FHLB Collateral	0
Federal Home Loan Bank of New York [Member] | Obligations of States and Political Subdivisions [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Fixed Income Securities Pledged For FHLB Collateral	0
Federal Home Loan Bank of New York [Member] | Commercial Mortgage Backed Securities [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Fixed Income Securities Pledged For FHLB Collateral	9.6
Federal Home Loan Bank of New York [Member] | Residential Mortgage Backed Securities [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Fixed Income Securities Pledged For FHLB Collateral	$ 79.8

Investments (Credit Concentrati

Investments (Credit Concentration Risk) (Details)	Jun. 30, 2018	Dec. 31, 2017
Investments [Abstract]
Maximum exposure to credit concentration risk of the Company's stockholder's equity other than certain U.S. government agencies	10.00%	10.00%

Investments (Net Investment Inc

Investments (Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Net Investment Income [Line Items]
Net investment income earned	$ 45,553	$ 41,430	$ 88,784	$ 78,849
Fixed Income Securities [Member]
Net Investment Income [Line Items]
Net investment income earned	43,774	37,668	85,815	74,559
Equity Securities [Member]
Net Investment Income [Line Items]
Net investment income earned	1,820	1,419	3,797	2,887
Short-Term Investments [Member]
Net Investment Income [Line Items]
Net investment income earned	611	377	1,134	627
Other Investments [Member]
Net Investment Income [Line Items]
Net investment income earned	2,094	5,231	3,657	6,834
Investment Expenses [Member]
Net Investment Income [Line Items]
Net investment income earned	$ (2,746)	$ (3,265)	$ (5,619)	$ (6,058)

Investments (OTTI) (Details)

Investments (OTTI) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Investments [Abstract]
OTTI Charges	$ 2,821	$ 1,217	$ 4,033	$ 4,692

Investments (Components Of Net

Investments (Components Of Net Realized and Unrealized Gains and Losses (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Gain (Loss) on Investments [Line Items]
Net realized (losses) gains on disposals of securities, fixed income securities		$ (1,174)	$ 2,606	$ (4,509)	$ 4,570
Total net realized gains on the disposal of securities (excluding OTTI charges)		54	2,951	4,785	5,381
OTTI Charges		(2,821)	(1,217)	(4,033)	(4,692)
Net realized investment (losses) gains		(2,767)	1,734	752	689
Unrealized gains (losses) recognized in income on equity securities	[1]	1,115	0	(12,953)	0
Total net realized and unrealized (losses) gains		(1,652)	1,734	(12,201)	689
Unrealized holding gains (losses) on equity securities		2,300		(2,700)
Unrealized losses on equity securities sold during the period		(1,200)		(10,300)
Equity Securities [Member]
Gain (Loss) on Investments [Line Items]
Total net realized gains on the disposal of securities (excluding OTTI charges)		1,226	350	9,295	350
Short-Term Investments [Member]
Gain (Loss) on Investments [Line Items]
Total net realized gains on the disposal of securities (excluding OTTI charges)		2	0	(1)	0
Other Investments [Member]
Gain (Loss) on Investments [Line Items]
Total net realized gains on the disposal of securities (excluding OTTI charges)		$ 0	$ (5)	$ 0	$ 461
[1]	Includes unrealized holding gains (losses) of: (i) $2.3 million in Second Quarter 2018 and $(2.7) million in Six Months 2018 on equity securities remaining in our portfolio as of June 30, 2018; and (ii) $(1.2) million in Second Quarter 2018 and $(10.3) million in Six Months 2018 on equity securities sold during the period.

Investments (Net Realized Gains

Investments (Net Realized Gains (Losses) on Disposals) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Schedule of Realized Gains (Losses) on Disposals Excluding OTTI [Line Items]
HTM fixed income securities Gains	$ 0	$ 44	$ 2	$ 44
HTM fixed income securities Losses	0	0	0	(1)
Equity securities Gains	1,226		9,625
Equity securities Losses	0		(330)
Short-term investments Gains	2	0	3	2
Short-term investments Losses	0	0	(4)	(2)
Other investments Gains	0	0	0	480
Other investments Losses	0	(5)	0	(19)
Net realized investment gains on disposals	54	2,951	4,785	5,381
Sale of fixed income securities, available-for-sale	262,900	122,300	938,276	717,072
Sale of equity securities	2,900		43,590
Sale of equity securities, available-for-sale		800		6,289
Fixed Maturities [Member]
Schedule of Realized Gains (Losses) on Disposals Excluding OTTI [Line Items]
AFS fixed income securities Gains	1,971	2,715	4,594	6,267
AFS fixed income securities Losses	(3,145)	(153)	(9,105)	(1,740)
Equity Securities [Member]
Schedule of Realized Gains (Losses) on Disposals Excluding OTTI [Line Items]
AFS fixed income securities Gains		350		350
AFS fixed income securities Losses		0		0
Net realized investment gains on disposals	$ 1,226	$ 350	$ 9,295	$ 350

Indebtedness Indebtedness (Deta

Indebtedness Indebtedness (Details) $ in Millions	Jun. 30, 2018USD ($)
One Point Seventy Five Percent Borrowing From Federal Home Loan Bank Due March 20, 2018 [Member]
Short-term Debt [Line Items]
Federal Home Loan Bank Advances	$ 75
Federal Home Loan Bank, Advances, Interest Rate	1.75%
One Point Ninety Eight Percent Borrowing From Federal Home Loan Bank Due April 18, 2018 [Member]
Short-term Debt [Line Items]
Federal Home Loan Bank Advances	$ 55
Federal Home Loan Bank, Advances, Interest Rate	1.98%

Fair Value Measurements (Quanti

Fair Value Measurements (Quantitative Disclosures of Fair Value Assets) (Details) - USD ($) $ in Thousands		6 Months Ended
		Jun. 30, 2018	Dec. 31, 2017
Percentage increase in long-term debt		1.00%
Investments Measured at Fair Value Using Net Asset Value		$ 27,100	$ 23,700
Available-for-sale Securities, Fixed Income Securities		5,137,653	5,162,522
Equity securities, available-for-sale			182,705
Equity securities		176,578
Total AFS securities		5,137,653	5,345,227
Short-term investments		164,118	165,555
Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities		5,137,653	5,162,522
Equity securities, available-for-sale			182,705
Equity securities		176,578
Total AFS securities			5,345,227
Short-term investments		164,118	165,555
Total assets measured at fair value		5,478,349	5,510,782
U.S. Government and Government Agencies [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities		38,896	49,740
Foreign Government [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities		17,982	18,555
Obligations of States and Political Subdivisions [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities		1,253,667	1,582,970
Corporate Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities		1,614,484	1,617,468
Collateralized Loan Obligations and Other Asset Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities		771,597	795,458
Commercial Mortgage Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities		451,593	383,449
Residential Mortgage Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities		989,434	714,882
Common Stock [Member] | Fair Value, Measurements, Recurring [Member]
Equity securities, available-for-sale	[1]		167,757
Equity securities	[1]	172,157
Preferred Stock [Member] | Fair Value, Measurements, Recurring [Member]
Equity securities, available-for-sale			14,948
Equity securities		4,421
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities	[2]	22,479	24,652
Equity securities, available-for-sale	[2]		153,588
Equity securities	[2]	149,459
Total AFS securities	[2]		178,240
Short-term investments	[2]	163,120	165,555
Total assets measured at fair value	[2]	335,058	343,795
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | U.S. Government and Government Agencies [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities	[2]	22,479	24,652
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Foreign Government [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities	[2]	0	0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Obligations of States and Political Subdivisions [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities	[2]	0	0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Corporate Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities	[2]	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, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities	[2]	0	0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Commercial Mortgage Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities	[2]	0	0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Residential Mortgage Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities	[2]	0	0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Common Stock [Member] | Fair Value, Measurements, Recurring [Member]
Equity securities, available-for-sale	[1],[2]		138,640
Equity securities	[1],[2]	145,038
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Preferred Stock [Member] | Fair Value, Measurements, Recurring [Member]
Equity securities, available-for-sale	[2]		14,948
Equity securities	[2]	4,421
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities	[2]	5,111,985	5,131,316
Equity securities, available-for-sale	[2]		0
Equity securities	[2]	0
Total AFS securities	[2]		5,131,316
Short-term investments	[2]	998	0
Total assets measured at fair value	[2]	5,112,983	5,131,316
Significant Other Observable Inputs (Level 2) [Member] | U.S. Government and Government Agencies [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities	[2]	16,417	25,088
Significant Other Observable Inputs (Level 2) [Member] | Foreign Government [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities	[2]	17,982	18,555
Significant Other Observable Inputs (Level 2) [Member] | Obligations of States and Political Subdivisions [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities	[2]	1,253,667	1,582,970
Significant Other Observable Inputs (Level 2) [Member] | Corporate Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities	[2]	1,614,484	1,617,468
Significant Other Observable Inputs (Level 2) [Member] | Collateralized Loan Obligations and Other Asset Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities	[2]	768,408	795,458
Significant Other Observable Inputs (Level 2) [Member] | Commercial Mortgage Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities	[2]	451,593	376,895
Significant Other Observable Inputs (Level 2) [Member] | Residential Mortgage Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities	[2]	989,434	714,882
Significant Other Observable Inputs (Level 2) [Member] | Common Stock [Member] | Fair Value, Measurements, Recurring [Member]
Equity securities, available-for-sale	[1],[2]		0
Equity securities	[1],[2]	0
Significant Other Observable Inputs (Level 2) [Member] | Preferred Stock [Member] | Fair Value, Measurements, Recurring [Member]
Equity securities, available-for-sale	[2]		0
Equity securities	[2]	0
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities		3,189	6,554
Equity securities, available-for-sale			5,398
Equity securities		0
Total AFS securities			11,952
Short-term investments		0	0
Total assets measured at fair value		3,189	11,952
Significant Unobservable Inputs (Level 3) [Member] | U.S. Government and Government Agencies [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities		0	0
Significant Unobservable Inputs (Level 3) [Member] | Foreign Government [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities		0	0
Significant Unobservable Inputs (Level 3) [Member] | Obligations of States and Political Subdivisions [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities		0	0
Significant Unobservable Inputs (Level 3) [Member] | Corporate Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities		0	0
Significant Unobservable Inputs (Level 3) [Member] | Collateralized Loan Obligations and Other Asset Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities		3,189	0
Significant Unobservable Inputs (Level 3) [Member] | Commercial Mortgage Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities		0	6,554
Significant Unobservable Inputs (Level 3) [Member] | Residential Mortgage Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fixed Income Securities		0	0
Significant Unobservable Inputs (Level 3) [Member] | Common Stock [Member] | Fair Value, Measurements, Recurring [Member]
Equity securities, available-for-sale	[1]		5,398
Equity securities	[1]	0
Significant Unobservable Inputs (Level 3) [Member] | Preferred Stock [Member] | Fair Value, Measurements, Recurring [Member]
Equity securities, available-for-sale			$ 0
Equity securities		$ 0
[1]	Investments amounting to $27.1 million at June 30, 2018, and $23.7 million at December 31, 2017, were measured at fair value using net asset value per share (or its practical expedient) and have not been classified in the fair value hierarchy. 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.
[2]	There were no transfers of securities between Level 1 and Level 2.

Fair Value Measurements (Change

Fair Value Measurements (Change in Fair Value of Securities Using Level 3 Inputs) (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018USD ($)
Commercial Mortgage Backed Securities [Member] | AFS Fixed Maturity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, December 31, 2017	$ 6,554
Total net (losses) gains for the period included in OCI	0
Total net (losses) gains for the period included in net income	0
Purchases	0
Sales	0
Issuances	0
Settlements	0
Transfers into Level 3	0
Transfers out of Level 3	(6,554)
Fair value, June 30, 2018	0
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total net (losses) gains for the period included in OCI	0
Total net (losses) gains for the period included in net income	0
Purchases	0
Sales	0
Issuances	0
Settlements	0
Transfers into Level 3	0
Transfers out of Level 3	(5,398)
Fair value, June 30, 2018	0
Equity Securities [Member] | Available-for-sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, December 31, 2017	5,398
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 OCI	0
Total net (losses) gains for the period included in net income	0
Purchases	3,189
Sales	0
Issuances	0
Settlements	0
Transfers into Level 3	0
Transfers out of Level 3	0
Fair value, June 30, 2018	3,189
Collateralized Loan Obligations and Other Asset Backed Securities [Member] | Available-for-sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, December 31, 2017	$ 0

Fair Value Measurements (Quan49

Fair Value Measurements (Quantitative Information of Our Financial Assets and Liabilities That Were Disclosed at Fair Value) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities, fair value	$ 43,373	$ 44,100
Seven Point Twenty Five Percent Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	57,231	61,391
Six Point Seventy Percent Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	108,453	116,597
Five Point Eight Hundred Seventy Five Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	186,924	186,332
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	23,979	24,270
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	23,915	24,210
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	58,483	60,334
Long-term Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	458,985	473,134
Obligations of States and Political Subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities, fair value	23,260	26,261
Corporate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities, fair value	20,113	17,839
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities, fair value	0	0
Long-term debt, fair value	186,924	186,332
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 Eight Hundred Seventy Five Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	186,924	186,332
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]
Held-to-maturity securities, 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]
Held-to-maturity securities, fair value	0	0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities, fair value	34,888	38,567
Long-term debt, fair value	272,061	286,802
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	57,231	61,391
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	108,453	116,597
Significant Other Observable Inputs (Level 2) [Member] | Five Point Eight Hundred Seventy Five Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	0	0
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	23,979	24,270
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	23,915	24,210
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	58,483	60,334
Significant Other Observable Inputs (Level 2) [Member] | Obligations of States and Political Subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities, fair value	23,260	26,261
Significant Other Observable Inputs (Level 2) [Member] | Corporate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities, fair value	11,628	12,306
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities, fair value	8,485	5,533
Long-term debt, fair value	0	0
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 Eight 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 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]
Held-to-maturity securities, fair value	0	0
Significant Unobservable Inputs (Level 3) [Member] | Corporate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities, fair value	$ 8,485	$ 5,533

Reinsurance (List of Direct, As

Reinsurance (List of Direct, Assumed, and Ceded Reinsurance Amounts) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Premiums written:
Direct	$ 753,363	$ 706,408	$ 1,467,597	$ 1,390,228
Assumed	6,536	6,488	12,807	12,179
Ceded	(104,651)	(99,082)	(200,596)	(189,889)
Net	655,248	613,814	1,279,808	1,212,518
Premiums earned:
Direct	696,723	654,588	1,380,456	1,301,316
Assumed	6,612	6,063	12,736	11,842
Ceded	(98,499)	(92,621)	(196,528)	(184,274)
Net	604,836	568,030	1,196,664	1,128,884
Loss and loss expenses incurred:
Direct	391,014	389,550	811,930	731,672
Assumed	2,364	7,766	10,368	12,203
Ceded	(27,050)	(55,757)	(71,029)	(84,844)
Net	366,328	341,559	751,269	659,031
National Flood Insurance Program [Member]
Premiums written:
Ceded	(66,341)	(63,808)	(123,010)	(120,142)
Premiums earned:
Ceded	(60,143)	(57,655)	(119,134)	(114,932)
Loss and loss expenses incurred:
Ceded	$ (10,261)	$ (15,140)	$ (25,980)	$ (21,681)

Reinsurance (Ceded Premiums and

Reinsurance (Ceded Premiums and Losses Related to Flood Operations) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Ceded premiums written	$ (104,651)	$ (99,082)	$ (200,596)	$ (189,889)
Ceded premiums earned	(98,499)	(92,621)	(196,528)	(184,274)
Ceded loss and loss expenses incurred	(27,050)	(55,757)	(71,029)	(84,844)
National Flood Insurance Program [Member]
Ceded premiums written	(66,341)	(63,808)	(123,010)	(120,142)
Ceded premiums earned	(60,143)	(57,655)	(119,134)	(114,932)
Ceded loss and loss expenses incurred	$ (10,261)	$ (15,140)	$ (25,980)	$ (21,681)
Percentage of NFIP claims ceded by federal government			100.00%

Reserve for Loss and Loss Exp52

Reserve for Loss and Loss Expense (Rollforward of Reserve for Loss and Loss Expense) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Liability for Catastrophe Claims [Line Items]
Increase in current year loss and loss expense incurred	$ 72,000
Increase in non catastrophe property losses	44,000
Non catastrophe property losses	188,700
Gross reserve for loss and loss expense, at beginning of year	3,771,240	$ 3,691,719
Less: reinsurance recoverable on unpaid loss and loss expense, at beginning of year	585,855	611,200
Net reserve for loss and loss expense, at beginning of year	3,185,385	3,080,519
Incurred loss and loss expense for claims occurring in the current year	756,855	684,877
Total incurred loss and loss expense	751,269	659,031
Paid loss and loss expense for claims occurring in the current year	214,169	171,724
Paid loss and loss expense for claims occurring in the prior years	457,441	425,521
Total paid loss and loss expense	671,610	597,245
Net reserve for loss and loss expense, at end of period	3,265,044	3,142,305
Add: reinsurance recoverable on unpaid loss and loss expense, at end of period	539,321	588,916
Gross reserve for loss and loss expense, at end of period	3,804,365	3,731,221
Change in Historical Claim Rate Experience [Member]
Liability for Catastrophe Claims [Line Items]
Prior year development	(5,586)	(25,846)
Change in Historical Claim Rate Experience [Member] | Property Insurance Product Line [Member]
Liability for Catastrophe Claims [Line Items]
Prior year development	6,400
Change in Historical Claim Rate Experience [Member] | Casualty Insurance Product Line [Member]
Liability for Catastrophe Claims [Line Items]
Prior year development	(12,000)
Change in Historical Claim Rate Experience [Member] | Casualty Insurance Product Line [Member] | Workers Compensation [Member]
Liability for Catastrophe Claims [Line Items]
Prior year development	(33,000)	(15,300)
Change in Historical Claim Rate Experience [Member] | Casualty Insurance Product Line [Member] | Commercial Automobile [Member]
Liability for Catastrophe Claims [Line Items]
Prior year development	15,000	21,000
Change in Historical Claim Rate Experience [Member] | Casualty Insurance Product Line [Member] | Excess And Surplus Operations [Member]
Liability for Catastrophe Claims [Line Items]
Prior year development	$ 6,000
Change in Historical Claim Rate Experience [Member] | Casualty Insurance Product Line [Member] | General Liability [Member]
Liability for Catastrophe Claims [Line Items]
Prior year development		(37,400)
Change in Historical Claim Rate Experience [Member] | Casualty Insurance Product Line [Member] | Personal Automobile [Member]
Liability for Catastrophe Claims [Line Items]
Prior year development		$ 4,000

Segment Information Narrative (

Segment Information Narrative (Details)	6 Months Ended
	Jun. 30, 2018
Number of Operating Segments	4

Segment Information (Revenue by

Segment Information (Revenue by Segment) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Total net premiums earned	$ 604,836	$ 568,030	$ 1,196,664	$ 1,128,884
Other income	3,179	3,291	5,358	6,532
Net investment income	45,553	41,430	88,784	78,849
Net realized and unrealized investment (losses) gains	(1,652)	1,734	(12,201)	689
Total investment revenues	43,901	43,164	76,583	79,538
Total revenues	651,916	614,485	1,278,605	1,214,954
Standard Commercial Lines [Member]
Segment Reporting Information [Line Items]
Total net premiums earned	478,894	446,610	946,084	887,884
Other income	2,882	3,016	4,708	5,876
Standard Commercial Lines [Member] | Commercial Automobile [Member]
Segment Reporting Information [Line Items]
Total net premiums earned	122,104	108,316	240,335	215,445
Standard Commercial Lines [Member] | Workers Compensation [Member]
Segment Reporting Information [Line Items]
Total net premiums earned	80,021	79,460	158,844	158,786
Standard Commercial Lines [Member] | General Liability [Member]
Segment Reporting Information [Line Items]
Total net premiums earned	153,002	141,503	302,831	281,487
Standard Commercial Lines [Member] | Commercial Property [Member]
Segment Reporting Information [Line Items]
Total net premiums earned	82,162	78,052	162,488	154,443
Standard Commercial Lines [Member] | Business Owners' Policies [Member]
Segment Reporting Information [Line Items]
Total net premiums earned	25,829	24,989	51,420	49,834
Standard Commercial Lines [Member] | Bonds Segment [Member]
Segment Reporting Information [Line Items]
Total net premiums earned	8,335	6,986	16,469	13,484
Standard Commercial Lines [Member] | Other Commercial [Member]
Segment Reporting Information [Line Items]
Total net premiums earned	4,559	4,288	8,989	8,529
Standard Personal Lines [Member]
Segment Reporting Information [Line Items]
Total net premiums earned	75,974	71,947	150,582	143,529
Other income	297	275	649	656
Standard Personal Lines [Member] | Personal Automobile [Member]
Segment Reporting Information [Line Items]
Total net premiums earned	41,810	37,663	82,252	74,613
Standard Personal Lines [Member] | Homeowners [Member]
Segment Reporting Information [Line Items]
Total net premiums earned	32,223	32,467	64,424	65,167
Standard Personal Lines [Member] | Other Personal [Member]
Segment Reporting Information [Line Items]
Total net premiums earned	1,644	1,542	3,257	3,093
Excess And Surplus Operations [Member]
Segment Reporting Information [Line Items]
Total net premiums earned	53,147	52,764	105,356	104,003
Other income	0	0	1	0
Excess And Surplus Operations [Member] | General Liability [Member]
Segment Reporting Information [Line Items]
Total net premiums earned	39,379	39,054	77,919	76,966
Excess And Surplus Operations [Member] | Commercial Property [Member]
Segment Reporting Information [Line Items]
Total net premiums earned	$ 13,768	$ 13,710	$ 27,436	$ 27,037

Segment Information (Income Bef

Segment Information (Income Before and After Federal Income Tax) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Net investment income	$ 45,553	$ 41,430	$ 88,784	$ 78,849
Net realized and unrealized investment (losses) gains	(1,652)	1,734	(12,201)	689
Total investment income, before federal income tax	43,901	43,164	76,583	79,538
Tax on investment income	7,617	11,734	12,843	21,336
Total investment income, after federal income tax	36,284	31,430	63,740	58,202
Standard Commercial Lines [Member]
Segment Reporting Information [Line Items]
Underwriting gain (loss), before federal income tax	41,016	34,759	47,820	77,305
Underwriting gain (loss), after federal income tax	$ 32,403	$ 22,593	$ 37,778	$ 50,248
Combined ratio	91.40%	92.20%	94.90%	91.20%
Standard Personal Lines [Member]
Segment Reporting Information [Line Items]
Underwriting gain (loss), before federal income tax	$ 4,805	$ (5,768)	$ 3,299	$ (662)
Underwriting gain (loss), after federal income tax	$ 3,796	$ (3,749)	$ 2,606	$ (430)
Combined ratio	93.70%	108.00%	97.80%	100.50%
Excess And Surplus Operations [Member]
Segment Reporting Information [Line Items]
Underwriting gain (loss), before federal income tax	$ (7,789)	$ 1,319	$ (8,354)	$ 2,889
Underwriting gain (loss), after federal income tax	$ (6,154)	$ 857	$ (6,600)	$ 1,878
Combined ratio	114.70%	97.50%	107.90%	97.20%

Segment Information (Reconcilia

Segment Information (Reconciliation of Segment Results to Income Before Federal Income Tax (Details)) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Investment income, before federal income tax	$ 43,901	$ 43,164	$ 76,583	$ 79,538
Interest expense	(6,125)	(6,081)	(12,277)	(12,187)
Corporate expenses	(3,283)	(8,464)	(14,615)	(20,380)
Income before federal income tax	72,525	58,929	92,456	126,503
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	41,016	34,759	47,820	77,305
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	4,805	(5,768)	3,299	(662)
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	(7,789)	1,319	(8,354)	2,889
Operating Segments [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total all segments	$ 81,933	$ 73,474	$ 119,348	$ 159,070

Retirement Plans (Components of

Retirement Plans (Components of Net Periodic Benefit Cost) (Details) - Pension Plan [Member] - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Interest cost		$ 3,095	$ 3,110	$ 6,190	$ 6,221
Expected return on plan assets		(5,681)	(4,855)	(11,363)	(9,709)
Amortization of unrecognized net actuarial loss		493	482	987	963
Total net periodic benefit	[1]	$ (2,093)	$ (1,263)	$ (4,186)	$ (2,525)
[1]	The components of net periodic benefit cost 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]	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.78%	4.41%
Effective interest rate for calculation of interest cost	3.46%	3.84%
Expected return on plan assets	6.36%	6.24%

Comprehensive Income (Component

Comprehensive Income (Components of Comprehensive Income-Gross and Net of Tax) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Net income, Gross	$ 72,525	$ 58,929	$ 92,456	$ 126,503
Unrealized holding (losses) gains during the period, Gross	(23,993)	35,887	(109,308)	61,672
Non-credit portion of OTTI recognized in OCI, Gross		6		6
Amounts reclassified into net income: HTM securities, Gross	(8)	(43)	(20)	(92)
Amounts reclassified into net income: Realized losses (gains) on disposals of AFS securities, Gross	2,870	(1,885)	7,419	(375)
Total unrealized (losses) gains on investment securities, Gross	(21,131)	33,965	(101,909)	61,211
Amount reclassified into net income: Net actuarial loss, Gross	531	508	1,063	1,015
Total defined pension and other post-retirement benefit plans, Gross	531	508	1,063	1,015
Other comprehensive (loss) income, Gross	(20,600)	34,473	(100,846)	62,226
Comprehensive income (loss) before tax	51,925	93,402	(8,390)	188,729
Net income, Tax	13,706	17,503	14,712	34,637
Unrealized holding (losses) gains during the period, Tax	(5,038)	12,561	(22,955)	21,585
Non-credit portion of OTTI recognized in OCI, Tax		2		2
Amounts reclassified into net income: HTM securities, Tax	(2)	(15)	(4)	(32)
Amounts reclassified into net income: Realized losses (gains) on disposals of AFS securities, Tax	603	(660)	1,558	(131)
Total unrealized (losses) gains on investment securities, Tax	(4,437)	11,888	(21,401)	21,424
Amount reclassified into net income: Net actuarial loss, Tax	111	178	223	355
Total defined pension and other post-retirement benefit plans, Tax	111	178	223	355
Other comprehensive (loss) income, Tax	(4,326)	12,066	(21,178)	21,779
Comprehensive income (loss), Tax	9,380	29,569	(6,466)	56,416
Net income	58,819	41,426	77,744	91,866
Unrealized holding (losses) gains arising during period	(18,955)	23,326	(86,353)	40,087
Non-credit portion of OTTI recognized in OCI		4		4
Amounts reclassified into net income: HTM Securities	(6)	(28)	(16)	(60)
Amounts reclassified into net income: Realized losses (gains) on disposals of available-for-sale securities	2,267	(1,225)	5,861	(244)
Total unrealized (losses) gains on investment securities	(16,694)	22,077	(80,508)	39,787
Amount reclassified into net income: Net actuarial loss	420	330	840	660
Total defined benefit pension and post-retirement plans	420	330	840	660
Other comprehensive (loss) income	(16,274)	22,407	(79,668)	40,447
Comprehensive income (loss)	$ 42,545	$ 63,833	$ (1,924)	$ 132,313

Comprehensive Income (Compone60

Comprehensive Income (Components of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2017			$ 20,170
Amounts reclassified from AOCI, Non-credit OTTI			0
Amounts reclassified from AOCI, HTM related	$ (6)	$ (28)	(16)	$ (60)
Amounts reclassified from AOCI, All Other	2,267	(1,225)	5,861	(244)
OCI before reclassifications, Defined Benefit Pension and Post Retirement Plans			0
Amount reclassified into net income: Net actuarial loss	420	330	840	660
Other comprehensive income	(16,274)	22,407	(79,668)	40,447
Other Comprehensive Income, Defined Benefit Pension and Post Retirement Plans, Adjustment, Net of Tax	420	$ 330	840	660
Ending Balance, June 30, 2018	(84,517)		(84,517)
Available-for-sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2017			80,648
Cumulative effect adjustment	(12,792)		(12,792)
OCI before reclassifications			(86,353)
Other comprehensive income			(80,492)
Ending Balance, June 30, 2018	(12,636)		(12,636)
Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2017			80,575
Cumulative effect adjustment	(12,806)		(12,806)
OCI before reclassifications			(86,353)
Amounts reclassified from AOCI			5,845
Other comprehensive income			(80,508)
Ending Balance, June 30, 2018	(12,739)		(12,739)
Accumulated Other-than-Temporary Impairment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2017			(59)
Cumulative effect adjustment	(12)		(12)
OCI before reclassifications			0
Other comprehensive income			0
Ending Balance, June 30, 2018	(71)		(71)
Accumulated Net Unrealized Investment Gain (Loss) [Member] | Held-to-maturity Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2017			(14)
Cumulative effect adjustment	(2)		(2)
OCI before reclassifications			0
Other comprehensive income			(16)
Ending Balance, June 30, 2018	(32)		(32)
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2017			(60,405)
Cumulative effect adjustment	(12,213)		(12,213)
Amount reclassified into net income: Net actuarial loss			840
Ending Balance, June 30, 2018	(71,778)		(71,778)
Accumulated other comprehensive income (loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2017			20,170
Cumulative effect adjustment	(25,019)		(25,019)
OCI before reclassifications			(86,353)
Amounts reclassified from AOCI			6,685
Other comprehensive income			(79,668)	$ 40,447
Ending Balance, June 30, 2018	$ (84,517)		(84,517)
Adjustments for New Accounting Pronouncement [Member] | Available-for-sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2017			67,856
Adjustments for New Accounting Pronouncement [Member] | Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2017			67,769
Adjustments for New Accounting Pronouncement [Member] | Accumulated Other-than-Temporary Impairment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2017			(71)
Adjustments for New Accounting Pronouncement [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member] | Held-to-maturity Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2017			(16)
Adjustments for New Accounting Pronouncement [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2017			(72,618)
Adjustments for New Accounting Pronouncement [Member] | Accumulated other comprehensive income (loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2017			$ (4,849)

Comprehensive Income (Reclassif

Comprehensive Income (Reclassification out of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Total net realized and unrealized (losses) gains	$ (1,652)	$ 1,734	$ (12,201)	$ 689
Net investment income	45,553	41,430	88,784	78,849
Loss and loss expense incurred	366,328	341,559	751,269	659,031
Other insurance expenses	80,994	82,874	164,234	164,925
Income before federal income tax	72,525	58,929	92,456	126,503
Total federal income tax expense	(13,706)	(17,503)	(14,712)	(34,637)
Net income	58,819	41,426	77,744	91,866
Reclassification out of AOCI
Net income	2,681	(923)	6,685	356
Pension Plan [Member] | Reclassification out of AOCI
Loss and loss expense incurred	113	111	225	221
Other insurance expenses	418	397	838	794
Income before federal income tax	531	508	1,063	1,015
Total federal income tax expense	(111)	(178)	(223)	(355)
Net income	420	330	840	660
Held-to-maturity Securities [Member] | Reclassification out of AOCI
Total net realized and unrealized (losses) gains	(7)	17	(6)	30
Net investment income	(1)	(60)	(14)	(122)
Income before federal income tax	(8)	(43)	(20)	(92)
Total federal income tax expense	2	15	4	32
Net income	(6)	(28)	(16)	(60)
Available-for-sale Securities [Member] | Reclassification out of AOCI
Total net realized and unrealized (losses) gains	2,870	(1,885)	7,419	(375)
Income before federal income tax	2,870	(1,885)	7,419	(375)
Total federal income tax expense	(603)	660	(1,558)	131
Net income	$ 2,267	$ (1,225)	$ 5,861	$ (244)

Federal Income Taxes (Schedule

Federal Income Taxes (Schedule of Effective Tax Rate Reconciliation) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Tax Disclosure [Abstract]
Statutory corporate tax rate percentage	21.00%	35.00%	21.00%	35.00%
Tax at statutory rate	$ 15,231	$ 20,625	$ 19,416	$ 44,276
Tax advantaged interest	(1,393)	(2,757)	(2,904)	(5,564)
Dividend received deduction	(210)	(625)	(336)	(956)
Stock-based compensation	(82)	(374)	(2,548)	(3,323)
Other	160	634	1,084	204
Total federal income tax expense	$ 13,706	$ 17,503	$ 14,712	$ 34,637