ProAssurance (PRA) 10-Q 6 Nov 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Oct. 31, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	PROASSURANCE CORP
Entity Central Index Key	1,127,703
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Amendment Flag	false
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding		53,636,174

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Investments
Fixed maturities, at fair value; cost or amortized cost, $2,192,705 and $2,257,188, respectively	$ 2,165,117	$ 2,280,242
Equity investments, at fair value; cost, $494,157 and $425,942, respectively	523,768	470,609
Short-term investments	204,573	432,126
Business owned life insurance	63,638	62,113
Investment in unconsolidated subsidiaries	390,738	330,591
Other investments, $32,868 and $52,301 at fair value, respectively, otherwise at cost or amortized cost	35,798	110,847
Total Investments	3,383,632	3,686,528
Cash and cash equivalents	87,559	134,495
Premiums receivable	283,687	238,085
Receivable from reinsurers on paid losses and loss adjustment expenses	9,533	7,317
Receivable from reinsurers on unpaid losses and loss adjustment expenses	332,555	335,585
Prepaid reinsurance premiums	51,437	39,916
Deferred policy acquisition costs	56,250	50,261
Deferred tax asset, net	17,962	9,930
Real estate, net	31,307	31,975
Intangible assets, net	78,320	82,952
Goodwill	210,725	210,725
Other assets	110,475	101,428
Total Assets	4,653,442	4,929,197
Policy liabilities and accruals
Reserve for losses and loss adjustment expenses	2,099,827	2,048,381
Unearned premiums	444,998	398,884
Reinsurance premiums payable	54,174	37,726
Total Policy Liabilities	2,598,999	2,484,991
Other liabilities	179,534	437,600
Debt less debt issuance costs	288,014	411,811
Total Liabilities	3,066,547	3,334,402
Shareholders' Equity
Common shares, par value $0.01 per share, 100,000,000 shares authorized, 62,987,485 and 62,824,523 shares issued, respectively	630	628
Additional paid-in capital	384,638	383,077
Accumulated other comprehensive income (loss), net of deferred tax expense (benefit) of ($5,224) and $5,218, respectively	(20,107)	14,911
Retained earnings	1,639,743	1,614,186
Treasury shares, at cost, 9,367,545 shares and 9,367,502 shares, respectively	(418,009)	(418,007)
Total Shareholders' Equity	1,586,895	1,594,795
Total Liabilities and Shareholders' Equity	$ 4,653,442	$ 4,929,197

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Debt Securities, at cost	$ 2,192,705	$ 2,257,188
Equity Investments, fair value, cost	494,157	425,942
Other investments, portion carried at fair value	$ 32,868	$ 52,301
Common shares, par value (in usd per share)	$ 0.01	$ 0.01
Common shares, shares authorized (in shares)	100,000,000	100,000,000
Common shares, shares issued (in shares)	62,987,485	62,824,523
Deferred tax expense (benefit) on accumulated other comprehensive income (loss)	$ (5,224)	$ 5,218
Treasury shares, number of shares (in shares)	9,367,545	9,367,502

Condensed Consolidated Statemen

Condensed Consolidated Statements of Changes in Capital (Unaudited) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Increase (Decrease) in Stockholders' Equity:
Beginning balance				$ 1,594,795	$ 1,798,702
Common shares issued for compensation and effect of shares reissued to stock purchase plan				1,348	1,875
Share-based compensation				4,083	7,110
Net effect of restricted and performance shares issued				(3,870)	(5,330)
Dividends to shareholders				(50,868)	(49,598)
Other comprehensive income (loss)				(38,434)	8,060
Net income		$ 31,228	$ 28,949	71,507	89,922
Ending balance		1,586,895	1,850,890	1,586,895	1,850,890
Accounting Standards Update 2016-01
Increase (Decrease) in Stockholders' Equity:
Cumulative-effect adjustment adoption of ASU	[1]					$ 8,334
Accounting Standards Update 2018-02
Increase (Decrease) in Stockholders' Equity:
Cumulative-effect adjustment adoption of ASU	[1]					0
Accounting Standards Update 2016-09
Increase (Decrease) in Stockholders' Equity:
Cumulative-effect adjustment adoption of ASU							$ 149
Common Stock
Increase (Decrease) in Stockholders' Equity:
Beginning balance				628	627
Net effect of restricted and performance shares issued				2	1
Ending balance		630	628	630	628
Additional Paid-in Capital
Increase (Decrease) in Stockholders' Equity:
Beginning balance				383,077	376,518
Common shares issued for compensation and effect of shares reissued to stock purchase plan				1,350	1,873
Share-based compensation				4,083	7,110
Net effect of restricted and performance shares issued				(3,872)	(5,331)
Ending balance		384,638	380,595	384,638	380,595
Additional Paid-in Capital | Accounting Standards Update 2016-09
Increase (Decrease) in Stockholders' Equity:
Cumulative-effect adjustment adoption of ASU							425
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity:
Beginning balance				14,911	17,399
Other comprehensive income (loss)				(38,434)	8,060
Ending balance		(20,107)	25,459	(20,107)	25,459
Accumulated Other Comprehensive Income (Loss) | Accounting Standards Update 2018-02
Increase (Decrease) in Stockholders' Equity:
Cumulative-effect adjustment adoption of ASU	[1]					3,416
Retained Earnings
Increase (Decrease) in Stockholders' Equity:
Beginning balance				1,614,186	1,824,088
Dividends to shareholders				(50,868)	(49,598)
Net income				71,507	89,922
Ending balance		1,639,743	1,864,136	1,639,743	1,864,136
Retained Earnings | Accounting Standards Update 2016-01
Increase (Decrease) in Stockholders' Equity:
Cumulative-effect adjustment adoption of ASU	[1]					8,334
Retained Earnings | Accounting Standards Update 2018-02
Increase (Decrease) in Stockholders' Equity:
Cumulative-effect adjustment adoption of ASU	[1]					$ (3,416)
Retained Earnings | Accounting Standards Update 2016-09
Increase (Decrease) in Stockholders' Equity:
Cumulative-effect adjustment adoption of ASU							$ (276)
Treasury Stock
Increase (Decrease) in Stockholders' Equity:
Beginning balance				(418,007)	(419,930)
Common shares issued for compensation and effect of shares reissued to stock purchase plan				(2)	2
Ending balance		$ (418,009)	$ (419,928)	$ (418,009)	$ (419,928)
[1]	See Note 1 for discussion of accounting guidance adopted during the period.

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Income and Comprehensive Income (Unaudited) - USD ($) shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues
Net premiums earned	$ 206,070,000	$ 192,303,000	$ 616,819,000	$ 555,559,000
Net investment income	23,266,000	23,729,000	67,677,000	69,592,000
Equity in earnings (loss) of unconsolidated subsidiaries	5,228,000	4,164,000	12,247,000	8,489,000
Net realized investment gains (losses):
OTTI losses	(86,000)	0	(490,000)	(419,000)
Portion of OTTI losses recognized in other comprehensive income before taxes	0	0	0	248,000
Net impairment losses recognized in earnings	(86,000)	0	(490,000)	(171,000)
Other net realized investment gains (losses)	12,459,000	7,749,000	3,141,000	18,981,000
Total net realized investment gains (losses)	12,373,000	7,749,000	2,651,000	18,810,000
Other income	2,388,000	510,000	7,155,000	4,581,000
Total revenues	249,325,000	228,455,000	706,549,000	657,031,000
Expenses
Net losses and loss adjustment expenses	147,605,000	129,356,000	439,120,000	364,058,000
Underwriting, policy acquisition and operating expenses
Operating expense	35,213,000	32,606,000	101,634,000	102,062,000
DPAC amortization	26,631,000	24,505,000	77,178,000	70,044,000
Segregated portfolio cells dividend expense (income)	5,255,000	2,891,000	9,787,000	14,076,000
Interest expense	3,599,000	4,124,000	11,262,000	12,402,000
Total expenses	218,303,000	193,482,000	638,981,000	562,642,000
Income before income taxes	31,022,000	34,973,000	67,568,000	94,389,000
Provision for income taxes
Current expense (benefit)	(1,637,000)	13,690,000	(4,140,000)	12,111,000
Deferred expense (benefit)	1,431,000	(7,666,000)	201,000	(7,644,000)
Total income tax expense (benefit)	(206,000)	6,024,000	(3,939,000)	4,467,000
Net income	31,228,000	28,949,000	71,507,000	89,922,000
Other comprehensive income (loss), after tax, net of reclassification adjustments	(3,964,000)	(605,000)	(38,434,000)	8,060,000
Comprehensive income (loss)	$ 27,264,000	$ 28,344,000	$ 33,073,000	$ 97,982,000
Earnings per share
Basic (in usd per share)	$ 0.58	$ 0.54	$ 1.33	$ 1.68
Diluted (in usd per share)	$ 0.58	$ 0.54	$ 1.33	$ 1.68
Weighted average number of common shares outstanding:
Basic (in shares)	53,620	53,413	53,585	53,377
Diluted (in shares)	53,773	53,614	53,735	53,586
Cash dividends declared per common share (in usd per share)	$ 0.31	$ 0.31	$ 0.93	$ 0.93

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Operating Activities
Net income	$ 71,507	$ 89,922
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization, net of accretion	16,544	21,024
(Increase) decrease in cash surrender value of BOLI	(1,525)	(1,518)
Net realized investment (gains) losses	(2,651)	(18,810)
Share-based compensation	4,145	7,110
Deferred income tax expense (benefit)	201	(7,644)
Policy acquisition costs, net of amortization (net deferral)	(5,989)	(4,882)
Equity in (earnings) loss of unconsolidated subsidiaries	(12,247)	(8,489)
Distributed earnings from unconsolidated subsidiaries	23,906	20,150
Other	490	(548)
Other changes in assets and liabilities:
Premiums receivable	(45,602)	(39,206)
Reinsurance related assets and liabilities	5,741	(45,401)
Other assets	(1,961)	1,188
Reserve for losses and loss adjustment expenses	51,446	47,270
Unearned premiums	46,114	49,446
Other liabilities	(3,725)	8,569
Net cash provided (used) by operating activities	146,394	118,181
Purchases of:
Fixed maturities, available for sale	(717,119)	(449,717)
Fixed maturities, trading	(33,086)	0
Equity investments	(169,160)	(127,916)
Other investments	(22,557)	(35,445)
Funding of qualified affordable housing project tax credit partnerships	(74)	(394)
Investment in unconsolidated subsidiaries	(54,496)	(30,530)
Proceeds from sales or maturities of:
Fixed maturities, available for sale	809,095	599,374
Equity investments	138,423	116,833
Other investments	21,853	16,479
Return of invested capital from unconsolidated subsidiaries	48,545	27,214
Net sales or maturities (purchases) of short-term investments	227,513	141,538
Unsettled security transactions, net change	(4,273)	(10,935)
Purchases of capital assets	(7,672)	(8,620)
Purchases of intangible assets	0	(2,984)
Repayments (advances) under Syndicate Credit Agreement	(878)	(3,698)
Other	(1,331)	953
Net cash provided (used) by investing activities	234,783	232,152
Financing Activities
Borrowings (repayments) under Revolving Credit Agreement	(123,000)	(48,000)
Repayments of Mortgage Loans	(1,047)	0
Dividends to shareholders	(299,894)	(298,704)
Capital contribution received from (return of capital to) external segregated portfolio cell owners	(267)	2,989
Other	(3,905)	(4,960)
Net cash provided (used) by financing activities	(428,113)	(348,675)
Increase (decrease) in cash and cash equivalents	(46,936)	1,658
Cash and cash equivalents at beginning of period	134,495	117,347
Cash and cash equivalents at end of period	87,559	119,005
Significant Non-Cash Transactions
Dividends declared and not yet paid	$ 16,622	$ 16,558

Basis of Presentation

Basis of Presentation	9 Months Ended
	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited Condensed Consolidated Financial Statements include the accounts of ProAssurance Corporation and its consolidated subsidiaries (ProAssurance, PRA or the Company). The financial statements have been prepared in accordance with GAAP for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and notes required by GAAP for complete financial statements. In the opinion of management, all adjustments considered necessary for a fair presentation, consisting of normal recurring adjustments, have been included. ProAssurance’s results for the nine months ended September 30, 2018 are not necessarily indicative of the results that may be expected for the year ending December 31, 2018 . The accompanying Condensed Consolidated Financial Statements should be read in conjunction with the Consolidated Financial Statements and Notes contained in ProAssurance’s December 31, 2017 report on Form 10-K. In connection with its preparation of the Condensed Consolidated Financial Statements, ProAssurance evaluated events that occurred subsequent to September 30, 2018 for recognition or disclosure in its financial statements and notes to financial statements. Beginning in the third quarter of 2018, ProAssurance operates in five reportable segments as follows: Specialty P&C , Workers' Compensation Insurance, Segregated Portfolio Cell Reinsurance, Lloyd's Syndicates and Corporate. For more information on the Company's segment reporting, including the nature of products and services provided and financial information by segment, refer to Note 13 . Reclassifications As a result of the third quarter 2018 segment reorganization, prior period segment information in Note 13 has been recast to conform to the Company's current segment reporting (see Note 13 for further information). Certain other insignificant prior period amounts have been reclassified to conform to the current period presentation. Accounting Policies Except as added below, the significant accounting policies followed by ProAssurance in making estimates that materially affect financial reporting are summarized in Note 1 of the Notes to Consolidated Financial Statements in ProAssurance’s December 31, 2017 report on Form 10-K. Retroactive Insurance Contracts In certain instances, ProAssurance’s insurance contracts cover losses both on a prospective basis and retroactive basis and, accordingly, ProAssurance bifurcates the prospective and retroactive provisions of these contracts and accounts for each component separately, where practicable. The prospective provisions of a contract are accounted for consistently with the Company’s other insurance contracts as discussed in Note 1 of the Notes to Consolidated Financial Statements in ProAssurance’s December 31, 2017 report on Form 10-K. Under the retroactive provisions of a contract, all premiums received and losses assumed are recognized immediately in earnings at the inception of the contract as all of the underlying loss events occurred in the past. If the estimated losses assumed differ from the premium received related to the retroactive provision of a contract, the resulting difference is deferred and recognized over the estimated claim payment period with the periodic amortization reflected in earnings as a component of net losses and loss adjustment expenses. Deferred gains are included as a component of the reserve for losses and loss adjustment expenses and deferred losses are included as a component of other assets on the Condensed Consolidated Balance Sheet. Subsequent changes to the estimated timing or amount of future loss payments in relation to the losses assumed under retroactive provisions also produce changes in deferred balances. Changes in such estimates are applied retrospectively and the resulting changes in deferred balances, together with periodic amortization, are included in earnings in the period of change. Other Liabilities Other liabilities consisted of the following: (In thousands) September 30, 2018 December 31, 2017 SPC dividends payable $ 54,591 $ 46,925 Unpaid dividends 16,622 267,292 All other 108,321 123,383 Total other liabilities $ 179,534 $ 437,600 SPC dividends payable are the cumulative undistributed earnings contractually payable to the external cell owners of the SPC s operated by Eastern Re and Inova Re , ProAssurance's Cayman Islands reinsurance subsidiaries. Unpaid dividends represent common stock dividends declared by ProAssurance's Board that had not yet been paid as of September 30, 2018 . Unpaid dividends at December 31, 2017 reflected a special dividend declared in the fourth quarter of 2017 that was paid in January 2018 . Accounting Changes Adopted Restricted Cash ( ASU 2016-18) Effective for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years, the FASB issued guidance related to the classification of restricted cash presented in the statement of cash flows with the objective of reducing diversity in practice. Under the new guidance, entities are required to include restricted cash and restricted cash equivalents with cash and cash equivalents when reconciling beginning-of-period and end-of-period total amounts as presented on the statement of cash flows. ProAssurance adopted the guidance as of January 1, 2018. Adoption of the guidance had no material effect on ProAssurance’s results of operations, financial position or cash flows. Intra-Entity Transfers of Assets Other than Inventory ( ASU 2016-16) Effective for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years, the FASB issued guidance which reduces the complexity in accounting standards related to the income tax consequences of intra-entity transfers of assets other than inventory between tax-paying components. A tax-paying component is an individual entity or group of entities that is consolidated for tax purposes. Under the new guidance, entities are required to recognize income tax consequences of an intra-entity transfer of assets other than inventory when the transfer occurs instead of delaying recognition until the asset has been sold to an outside party. ProAssurance adopted the guidance as of January 1, 2018. Adoption of the guidance had no material effect on ProAssurance’s results of operations, financial position or cash flows. Classification of Certain Cash Receipts and Cash Payments ( ASU 2016-15) Effective for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years, the FASB issued guidance related to the classification of certain cash receipts and cash payments presented in the statement of cash flows with the objective of reducing diversity in practice. ProAssurance adopted the guidance as of January 1, 2018 and elected to use the cumulative earnings approach for presenting distributions from equity method investees. Adoption of the guidance had no material effect on ProAssurance’s results of operations or financial position; however, ProAssurance reclassified approximately $20.2 million in distributions from unconsolidated subsidiaries from investing activities to operating activities in the Condensed Consolidated Statement of Cash Flows for the nine months ended September 30, 2017 . Revenue from Contracts with Customers ( ASU 2014-09) Effective for fiscal years beginning after December 15, 2017 the FASB issued guidance related to revenue from contracts with customers. The core principle of the new guidance is that revenue is recognized to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. ProAssurance adopted the guidance as of January 1, 2018 under the modified retrospective method. Adoption of the guidance had no material effect on ProAssurance’s results of operations, financial position or cash flows. Recognition and Measurement of Financial Assets and Financial Liabilities ( ASU 2016-01) Effective for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years, the FASB issued guidance that requires equity investments (except those accounted for under the equity method of accounting, or those that result in consolidation of the investee) to be measured at fair value with changes in fair value recognized in net income. The new guidance also specifies that an entity use the exit price notion when measuring the fair value of financial instruments for disclosure purposes and present financial assets and liabilities by measurement category and form of financial asset. Other provisions of the new guidance include: revised disclosure requirements related to the presentation in comprehensive income of changes in the fair value of liabilities; elimination, for public companies, of disclosure requirements relative to the methods and significant assumptions underlying fair values disclosed for financial instruments measured at amortized cost; and simplified impairment assessments for equity investments without readily determinable fair values. ProAssurance adopted the guidance as of January 1, 2018 using a modified retrospective application and recorded a cumulative-effect after-tax adjustment of approximately $8.3 million to beginning retained earnings in the Condensed Consolidated Statement of Changes in Capital for the nine months ended September 30, 2018 . LP s/ LLC s previously reported using the cost method are now reported at fair value with increases in fair value of approximately $5.2 million and $11.1 million recognized as a component of equity in earnings (loss) of unconsolidated subsidiaries on the Condensed Consolidated Statements of Income and Comprehensive Income for the three and nine months ended September 30, 2018 , respectively. Modification Accounting for Employee Share-Based Payment Awards ( ASU 2017-09) Effective for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years, the FASB issued guidance which reduces the complexity in accounting standards when there is a change in the terms or conditions of a share-based payment award. The new guidance clarifies that an entity should apply the modification accounting guidance if the value, vesting conditions or classification of the award changes. ProAssurance adopted the guidance as of January 1, 2018. Adoption of the guidance had no material effect on ProAssurance’s results of operations, financial position or cash flows. Reclassification of Certain Tax Effects from AOCI ( ASU 2018-02) Effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years, with early adoption permitted, the FASB issued guidance which permits a reclassification from AOCI to retained earnings for stranded tax effects resulting from the newly enacted federal corporate tax rate from the TCJA . The amount of the reclassification from AOCI to retained earnings will be the difference between the historical corporate tax rate and the newly enacted 21% corporate tax rate on deferred tax items originally established through OCI and not net income. The guidance allows entities to adopt in any interim or annual period for which financial statements have not yet been issued and apply the guidance either (1) in the period of adoption or (2) retrospectively to each period in which the effect of the change in the tax rate is recognized. ProAssurance adopted this guidance as of January 1, 2018 and elected to apply this guidance in the period of adoption using the specific identification method. Using a modified retrospective application, ProAssurance recorded a cumulative-effect adjustment which increased beginning AOCI by approximately $3.4 million and decreased beginning retained earnings by the same amount in the Condensed Consolidated Statement of Changes in Capital for the nine months ended September 30, 2018 . Adoption of this guidance had no material effect on ProAssurance's financial position, results of operations or cash flows. Technical Corrections and Improvements to Financial Instruments - Overall ( ASU 2018-03) Effective for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years beginning after June 15, 2018, the FASB amended the new standard on recognizing and measuring financial assets and financial liabilities to clarify certain aspects of the guidance. Under the amended guidance, an entity that uses the measurement alternative for equity investments without readily determinable fair values can change its measurement approach to a fair value method through an irrevocable election that would apply to that security and all identical or similar investments of the same issuer. Also, entities are required to use the prospective transition approach only for equity investments they elect to measure using the new measurement alternative. Additionally, the guidance clarifies how to apply the measurement alternative and presentation requirements for financial liabilities measured under the fair value option. ProAssurance adopted the guidance as of July 1, 2018 and adoption had no material effect on ProAssurance's financial position, results of operations or cash flows as ProAssurance does not have any equity investments without readily determinable fair values or financial liabilities measured under the fair value option. Accounting Changes Not Yet Adopted Leases ( ASU 2016-02) Effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years, the FASB issued guidance that requires a lessee to recognize for all leases (with the exception of short-term leases) a lease liability, which is a lessee's obligation to make lease payments arising from a lease, measured on a discounted basis, and a right-of-use asset, which is an asset that represents the lessee's right to use, or control the use of, a specified asset for the lease term. ProAssurance plans to adopt the guidance beginning January 1, 2019 using a modified retrospective application and plans to elect the transition option provided that allows companies to continue to apply legacy GAAP in comparative periods. As of September 30, 2018 , ProAssurance is currently in the process of evaluating all of its leases. As the majority of ProAssurance's leases are real estate operating leases and are not considered to be material, adoption of the guidance is not expected to have a material effect on ProAssurance’s results of operations, financial position or cash flows. In addition, ProAssurance's Revolving Credit Agreement contains a financial covenant regarding permitted leverage ratios based upon Consolidated Funded Indebtedness to Consolidated Total Capitalization; however, ProAssurance does not anticipate that the adoption of this guidance would have a material impact on the covenant. ProAssurance’s Mortgage Loans also contain a financial covenant regarding permitted leverage ratios, principally based upon SAP Consolidated Net Worth; however, as the NAIC is not anticipated to adopt the principles in the FASB guidance around capitalizing operating leases, adoption of the guidance would have no impact on the covenant. Premium Amortization on Purchased Callable Debt Securities ( ASU 2017-08) Effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years, the FASB issued guidance that will require the premium for certain callable debt securities to be amortized over a shorter period than is currently required. Currently amortization is permitted over the contractual life of the instrument and the guidance shortens the amortization to the earliest call date. The purpose of the guidance is to more closely align the amortization period of premiums to expectations incorporated in market pricing on the underlying securities. ProAssurance plans to adopt the guidance beginning January 1, 2019. As ProAssurance amortizes premium on callable debt securities to the earliest call date, adoption of the guidance is not expected to have a material effect on ProAssurance’s results of operations, financial position or cash flows. Derivatives and Hedging ( ASU 2017-12) Effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years, the FASB issued guidance to improve financial reporting of hedging relationships to better portray the entity's risk management activities in the consolidated financial statements. The new guidance eliminates the requirement to separately measure and report hedge ineffectiveness and requires the entire change in the fair value of a hedging instrument to be presented in the same income statement line as the hedged item. ProAssurance plans to adopt the guidance beginning January 1, 2019. ProAssurance's derivative instrument at September 30, 2018 is not designated as a hedging instrument; therefore, adoption is not expected to have a material effect on ProAssurance's results of operations, financial position or cash flows. Improvements to Nonemployee Share-Based Payment Accounting ( ASU 2018-07) Effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years, the FASB issued guidance which reduces the complexity in accounting for nonemployee share-based payment awards. The new guidance substantially aligns the accounting for nonemployee share-based payment awards with the accounting guidance for employee share-based payment awards with certain exceptions, including the inputs used in estimating the fair value of the nonemployee awards and the period of time and pattern of expense recognition. ProAssurance plans to adopt the guidance as of January 1, 2019. Adoption of the guidance is not expected to have a material effect on ProAssurance’s results of operations, financial position or cash flows. Improvements to Financial Instruments - Credit Losses ( ASU 2016-13) Effective for fiscal years beginning after December 15, 2019 and interim periods within those fiscal years, the FASB issued guidance that replaces the incurred loss impairment methodology, which delays recognition of credit losses until a probable loss has been incurred, with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. Under the new guidance, credit losses are required to be recorded through an allowance for credit losses account and the income statement reflects the measurement for newly recognized financial assets, as well as increases or decreases of expected credit losses that have taken place during the period. Credit losses on available-for-sale fixed maturity securities will be measured in a manner similar to current GAAP, although the new guidance requires that credit losses be presented as an allowance, rather than as a write-down of the asset, limited to the amount by which the fair value is below amortized cost. In addition, this guidance could impact ProAssurance's receivables from reinsurers; however, ProAssurance has not historically experienced material credit losses due to the financial condition of a reinsurer. ProAssurance plans to adopt the guidance beginning January 1, 2020 and is in the process of evaluating the effect the new guidance would have on its results of operations and financial position. Simplifying the Test for Goodwill Impairment ( ASU 2017-04) Effective for the fiscal years beginning after December 15, 2019 and interim periods within those fiscal years, the FASB issued guidance that simplifies the requirements to test goodwill for impairment for business entities that have goodwill reported in their financial statements. The guidance eliminates the second step of the impairment test which measures a goodwill impairment loss by comparing the implied fair value of a reporting unit's goodwill with the carrying amount. In addition, the guidance also eliminates the requirements for any reporting unit with a zero or negative carrying amount to perform a qualitative assessment. ProAssurance plans to adopt the guidance beginning January 1, 2020. Adoption is not expected to have a material effect on ProAssurance’s results of operations, financial position or cash flows. Changes to the Disclosure Requirements for Fair Value Measurement ( ASU 2018-13) Effective for fiscal years beginning after December 15, 2019 and interim periods within those fiscal years, the FASB issued guidance that eliminates, modifies and adds certain disclosure requirements related to fair value measurements. The new guidance eliminates the requirements to disclose the transfers between Level 1 and Level 2 of the fair value hierarchy, the policy for the timing of transfers between levels of the fair value hierarchy and the valuation process for Level 3 fair value measurements while it modifies existing disclosure requirements related to measurement uncertainty and the requirement to disclose the timing of liquidation of an investee's assets for investments in certain entities that calculate NAV . The new guidance also adds requirements to disclose changes in unrealized gains and losses included in OCI for recurring Level 3 fair value measurements as well as the range and weighted average used to develop significant unobservable inputs for Level 3 fair value measurements. An entity is permitted to early adopt any eliminated or modified disclosure requirements and delay adoption of the additional disclosure requirements until the guidance is effective. As of September 30, 2018 , ProAssurance has elected to early adopt the provisions that eliminate and modify certain disclosure requirements within Note 2 on a retrospective basis and adoption of these certain provisions had no material effect on ProAssurance’s results of operations, financial position or cash flows as it affected disclosures only. ProAssurance plans to adopt the additional disclosure requirements beginning January 1, 2020 and adoption is not expected to have a material effect on ProAssurance’s results of operations, financial position or cash flows. Intangibles - Goodwill and Other-Internal-Use Software ( ASU 2018-15) Effective for fiscal years beginning after December 15, 2019 and interim periods within those fiscal years, the FASB amended the new standard regarding accounting for implementation costs in cloud computing arrangements. The amended guidance substantially aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. ProAssurance plans to adopt the guidance beginning January 1, 2020. Adoption is not expected to have a material effect on ProAssurance’s results of operations, financial position or cash flows.

Fair Value Measurement

Fair Value Measurement	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurement	Fair Value Measurement Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. A three level hierarchy has been established for valuing assets and liabilities based on how transparent (observable) the inputs are that are used to determine fair value, with the inputs considered most observable categorized as Level 1 and those that are the least observable categorized as Level 3. Hierarchy levels are defined as follows: Level 1: quoted (unadjusted) market prices in active markets for identical assets and liabilities. For ProAssurance, Level 1 inputs are generally quotes for debt or equity securities actively traded in exchange or over-the-counter markets. Level 2: market data obtained from sources independent of the reporting entity (observable inputs). For ProAssurance, Level 2 inputs generally include quoted prices in markets that are not active, quoted prices for similar assets or liabilities, and results from pricing models that use observable inputs such as interest rates and yield curves that are generally available at commonly quoted intervals. Level 3: the reporting entity's own assumptions about market participant assumptions based on the best information available in the circumstances (non-observable inputs). For ProAssurance, Level 3 inputs are used in situations where little or no Level 1 or 2 inputs are available or are inappropriate given the particular circumstances. Level 3 inputs include results from pricing models for which some or all of the inputs are not observable, discounted cash flow methodologies, single non-binding broker quotes and adjustments to externally quoted prices that are based on management judgment or estimation. Fair values of assets measured at fair value on a recurring basis as of September 30, 2018 and December 31, 2017 are shown in the following tables. Where applicable, the tables also indicate the fair value hierarchy of the valuation techniques utilized to determine those fair values. For some assets, the inputs used to measure fair value may fall into different levels of the fair value hierarchy. When this is the case, the asset is categorized based on the level of the most significant input to the fair value measurement. Assessments of the significance of a particular input to the fair value measurement require judgment and consideration of factors specific to the assets being valued. September 30, 2018 Fair Value Measurements Using Total (In thousands) Level 1 Level 2 Level 3 Fair Value Assets: Fixed maturities, available for sale U.S. Treasury obligations $ — $ 125,072 $ — $ 125,072 U.S. Government-sponsored enterprise obligations — 35,882 — 35,882 State and municipal bonds — 310,188 — 310,188 Corporate debt, multiple observable inputs 2,367 1,229,540 — 1,231,907 Corporate debt, limited observable inputs — — 9,405 9,405 Residential mortgage-backed securities — 187,460 — 187,460 Agency commercial mortgage-backed securities — 13,544 — 13,544 Other commercial mortgage-backed securities — 31,411 — 31,411 Other asset-backed securities — 180,307 7,159 187,466 Fixed maturities, trading Corporate debt — 32,782 — 32,782 Equity investments Financial 77,159 — — 77,159 Utilities/Energy 59,460 — — 59,460 Consumer oriented 58,478 — — 58,478 Industrial 50,776 — — 50,776 Bond funds 211,513 — — 211,513 All other 45,966 — — 45,966 Short-term investments 171,061 33,512 — 204,573 Other investments — 32,862 6 32,868 Other assets — 2,852 — 2,852 Total assets categorized within the fair value hierarchy $ 676,780 $ 2,215,412 $ 16,570 2,908,762 Assets carried at NAV, which approximates fair value and which are not categorized within the fair value hierarchy, reported as a part of: Equity investments 20,416 Investment in unconsolidated subsidiaries 287,575 Total assets at fair value $ 3,216,753 December 31, 2017 Fair Value Measurements Using Total (In thousands) Level 1 Level 2 Level 3 Fair Value Assets: Fixed maturities, available for sale U.S. Treasury obligations $ — $ 133,627 $ — $ 133,627 U.S. Government-sponsored enterprise obligations — 20,956 — 20,956 State and municipal bonds — 632,243 — 632,243 Corporate debt, multiple observable inputs 2,371 1,151,084 — 1,153,455 Corporate debt, limited observable inputs — — 13,703 13,703 Residential mortgage-backed securities — 196,789 1,055 197,844 Agency commercial mortgage-backed securities — 10,742 — 10,742 Other commercial mortgage-backed securities — 15,961 — 15,961 Other asset-backed securities — 97,780 3,931 101,711 Equity investments Financial 76,051 — — 76,051 Utilities/Energy 54,388 — — 54,388 Consumer oriented 54,529 — — 54,529 Industrial 53,936 — — 53,936 Bond funds 156,563 — — 156,563 All other 75,142 — — 75,142 Short-term investments 404,204 27,922 — 432,126 Other investments 607 31,155 409 32,171 Other assets — 1,731 — 1,731 Total assets categorized within the fair value hierarchy $ 877,791 $ 2,319,990 $ 19,098 3,216,879 Assets carried at NAV, which approximates fair value and which are not categorized within the fair value hierarchy, reported as a part of: Investment in unconsolidated subsidiaries 210,759 Other investments 20,130 Total assets at fair value $ 3,447,768 The fair values for securities included in the Level 2 category, with the few exceptions described below, were developed by one of several third party, nationally recognized pricing services, including services that price only certain types of securities. Each service uses complex methodologies to determine values for securities and subject the values they develop to quality control reviews. Management selected a primary source for each type of security in the portfolio and reviewed the values provided for reasonableness by comparing data to alternate pricing services and to available market and trade data. Values that appeared inconsistent were further reviewed for appropriateness. Any value that did not appear reasonable was discussed with the service that provided the value and adjusted, if necessary. There were no material changes to the values supplied by the pricing services during the three and nine months ended September 30, 2018 and 2017 . Level 2 Valuations Below is a summary description of the valuation methodologies primarily used by the pricing services for securities in the Level 2 category, by security type: U.S. Treasury obligations were valued based on quoted prices for identical assets, or, in markets that are not active, quotes for similar assets, taking into consideration adjustments for variations in contractual cash flows and yields to maturity. U.S. Government-sponsored enterprise obligations were valued using pricing models that consider current and historical market data, normal trading conventions, credit ratings, and the particular structure and characteristics of the security being valued, such as yield to maturity, redemption options, and contractual cash flows. Adjustments to model inputs or model results were included in the valuation process when necessary to reflect recent regulatory, government or corporate actions or significant economic, industry or geographic events affecting the security’s fair value. State and municipal bonds were valued using a series of matrices that considered credit ratings, the structure of the security, the sector in which the security falls, yields, and contractual cash flows. Valuations were further adjusted, when necessary, to reflect the expected effect on fair value of recent significant economic or geographic events or ratings changes. Corporate debt, multiple observable inputs consisted primarily of corporate bonds, but also included a small number of bank loans. The methodology used to value Level 2 corporate bonds was the same as the methodology previously described for U.S. Government-sponsored enterprise obligations. Bank loans were valued based on an average of broker quotes for the loans in question, if available. If quotes were not available, the loans were valued based on quoted prices for comparable loans or, if the loan was newly issued, by comparison to similar seasoned issues. Broker quotes were compared to actual trade prices to permit assessment of the reliability of the quotes; unreliable quotes were not considered in quoted averages. Residential and commercial mortgage-backed securities were valued using a pricing matrix which considers the issuer type, coupon rate and longest cash flows outstanding. The matrix used was based on the most recently available market information. Agency and non-agency collateralized mortgage obligations were both valued using models that consider the structure of the security, current and historical information regarding prepayment speeds, ratings and ratings updates, and current and historical interest rate and interest rate spread data. Other asset-backed securities were valued using models that consider the structure of the security, monthly payment information, current and historical information regarding prepayment speeds, ratings and ratings updates, and current and historical interest rate and interest rate spread data. Spreads and prepayment speeds consider collateral type. Short-term investments were securities maturing within one year, carried at fair value which approximated the cost of the securities due to their short-term nature. Other investments consisted primarily of convertible bonds valued using a pricing model that incorporated selected dealer quotes as well as current market data regarding equity prices and risk free rates. If dealer quotes were unavailable for the security being valued, quotes for securities with similar terms and credit status were used in the pricing model. Dealer quotes selected for use were those considered most accurate based on parameters such as underwriter status and historical reliability. Other assets consisted of an interest rate cap derivative instrument, which is discussed in Note 9 , valued using a model which considers the volatilities from other instruments with similar maturities, strike prices, durations and forward yield curves. Level 3 Valuations Below is a summary description of the valuation methodologies used as well as quantitative information regarding securities in the Level 3 category, by security type: Level 3 Valuation Methodologies Corporate debt, limited observable inputs consisted of corporate bonds valued using dealer quotes for similar securities or discounted cash flow models using yields currently available for similar securities. Similar securities are defined as securities of comparable credit quality that have like terms and payment features. Assessments of credit quality were based on NRSRO ratings, if available, or were subjectively determined by management if not available. At September 30, 2018 , 79% of the securities were rated and the average rating was BBB+ . At December 31, 2017 , 84% of the securities were rated and the average rating was BBB+ . Residential mortgage-backed and other asset-backed securities consisted of securitizations of receivables valued using dealer quotes for similar securities or discounted cash flow models using yields currently available for similar securities. Similar securities are defined as securities of comparable credit quality that have like terms and payment features. Assessments of credit quality were based on NRSRO ratings, if available, or were subjectively determined by management if not available. At September 30, 2018 , 60% of the securities were rated and the average rating was AAA . At December 31, 2017 , 21% of the securities were rated and the average rating was AAA . Other investments consisted of convertible securities for which limited observable inputs were available at September 30, 2018 and December 31, 2017 . The securities were valued internally based on expected cash flows, including the expected final recovery, discounted at a yield that considered the lack of liquidity and the financial status of the issuer. Quantitative Information Regarding Level 3 Valuations Fair Value at ($ in thousands) September 30, 2018 December 31, 2017 Valuation Technique Unobservable Input Range Assets: Corporate debt, limited observable inputs $9,405 $13,703 Market Comparable Comparability Adjustment 0% - 5% (2.5%) Discounted Cash Flows Comparability Adjustment 0% - 5% (2.5%) Residential mortgage-backed and other asset-backed securities $7,159 $4,986 Market Comparable Comparability Adjustment 0% - 5% (2.5%) Discounted Cash Flows Comparability Adjustment 0% - 5% (2.5%) Other investments $6 $409 Discounted Cash Flows Comparability Adjustment 0% - 10% (5%) The significant unobservable inputs used in the fair value measurement of the above listed securities were the valuations of comparable securities with similar issuers, credit quality and maturity. Changes in the availability of comparable securities could result in changes in the fair value measurements. Fair Value Measurements - Level 3 Assets The following tables (the Level 3 Tables) present summary information regarding changes in the fair value of assets measured at fair value using Level 3 inputs. September 30, 2018 Level 3 Fair Value Measurements – Assets (In thousands) Corporate Debt Asset-backed Securities Other investments Total Balance June 30, 2018 $ 8,380 $ 9,420 $ 5 $ 17,805 Total gains (losses) realized and unrealized: Included in earnings, as a part of: Net investment income (37 ) 1 — (36 ) Net realized investment gains (losses) — — 1 1 Included in other comprehensive income (12 ) 15 — 3 Purchases 2,000 — — 2,000 Sales (926 ) — — (926 ) Transfers in — — — — Transfers out — (2,277 ) — (2,277 ) Balance September 30, 2018 $ 9,405 $ 7,159 $ 6 $ 16,570 Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end $ — $ — $ — $ — September 30, 2018 Level 3 Fair Value Measurements – Assets (In thousands) Corporate Debt Asset-backed Securities Other investments Total Balance December 31, 2017 $ 13,703 $ 4,986 $ 409 $ 19,098 Total gains (losses) realized and unrealized: Included in earnings, as a part of: Net investment income (111 ) 2 — (109 ) Net realized investment gains (losses) (8 ) — (37 ) (45 ) Included in other comprehensive income (140 ) (126 ) — (266 ) Purchases 8,005 16,678 — 24,683 Sales (5,475 ) (185 ) (366 ) (6,026 ) Transfers in 2,627 — — 2,627 Transfers out (9,196 ) (14,196 ) — (23,392 ) Balance September 30, 2018 $ 9,405 $ 7,159 $ 6 $ 16,570 Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end $ — $ — $ — $ — September 30, 2017 Level 3 Fair Value Measurements – Assets (In thousands) Corporate Debt Asset-backed Securities Other investments Total Balance June 30, 2017 $ 17,849 $ 3,005 $ 5 $ 20,859 Total gains (losses) realized and unrealized: Included in earnings, as a part of: Net investment income (52 ) — — (52 ) Included in other comprehensive income (18 ) (45 ) — (63 ) Purchases 1 580 — 581 Sales (858 ) — — (858 ) Transfers in 989 — 423 1,412 Transfers out (2,948 ) — — (2,948 ) Balance September 30, 2017 $ 14,963 $ 3,540 $ 428 $ 18,931 Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end $ — $ — $ — $ — September 30, 2017 Level 3 Fair Value Measurements – Assets (In thousands) Corporate Debt Asset-backed Securities Other investments Total Balance December 31, 2016 $ 14,810 $ 3,007 $ 3 $ 17,820 Total gains (losses) realized and unrealized: Included in earnings, as a part of: Net investment income (125 ) — — (125 ) Net realized investment gains (losses) 13 — (124 ) (111 ) Included in other comprehensive income (296 ) (47 ) 140 (203 ) Purchases 11,890 580 — 12,470 Sales (4,418 ) — (912 ) (5,330 ) Transfers in 999 — 1,321 2,320 Transfers out (7,910 ) — — (7,910 ) Balance September 30, 2017 $ 14,963 $ 3,540 $ 428 $ 18,931 Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end $ — $ — $ — $ — Transfers Transfers shown in the preceding Level 3 tables were as of the end of the quarter in which the transfer occurred. All transfers were to or from Level 2. All transfers during the three and nine months ended September 30, 2018 and 2017 related to securities held for which the level of market activity for identical or nearly identical securities varies from period to period. The securities were valued using multiple observable inputs when those inputs were available; otherwise the securities were valued using limited observable inputs. Fair Values Not Categorized At September 30, 2018 and December 31, 2017 , certain LP s/ LLC s and investment funds measure fund assets at fair value on a recurring basis and provide a NAV for ProAssurance's interest. The carrying value of these interests is based on the NAV provided and was considered to approximate the fair value of the interests. For investment in unconsolidated subsidiaries, ProAssurance recognizes any changes in the NAV of its interests in equity in earnings (loss) of unconsolidated subsidiaries during the period of change. In accordance with GAAP , the fair value of these investments was not classified within the fair value hierarchy. The amount of ProAssurance's unfunded commitments related to these investments as of September 30, 2018 and fair values of these investments as of September 30, 2018 and December 31, 2017 was as follows: Unfunded Fair Value (In thousands) September 30, September 30, December 31, Equity investments: Mortgage fund (1)* None $ 20,416 $ — Investment in unconsolidated subsidiaries: Private debt funds (2) $19,918 23,736 42,206 Long equity fund (3) None 6,899 7,847 Long/short equity funds (4) None 27,927 31,352 Non-public equity funds (5) $73,795 113,669 100,062 Multi-strategy fund of funds (6) None 9,447 9,100 Credit funds (7) $8,916 29,485 6,561 Long/short commodities fund (8) None 13,686 13,025 Strategy focused funds (9) $29,693 62,726 606 287,575 210,759 Other investments: Mortgage fund (1)* See above — 20,130 Total investments carried at NAV $ 307,991 $ 230,889 * In the first quarter of 2018, ProAssurance began presenting this investment previously reported as a part of other investments as a part of equity investments on the Condensed Consolidated Balance Sheet. Prior year amounts have not been reclassified. Below is additional information regarding each of the investments listed in the table above as of September 30, 2018 . (1) This investment fund is focused on the structured mortgage market. The fund will primarily invest in U.S. Agency mortgage-backed securities. Redemptions are allowed at the end of any calendar quarter with a prior notice requirement of 65 days and are paid within 45 days at the end of the redemption dealing day. (2) The investment is comprised of interests in three unrelated LP funds that are structured to provide interest distributions primarily through diversified portfolios of private debt instruments. One LP allows redemption by special consent; the other two do not permit redemption. Income and capital are to be periodically distributed at the discretion of the LP s over an anticipated time frame that spans from three to eight years. (3) The fund is a LP that holds long equities of public international companies. Redemptions are allowed at the end of any calendar month with a prior notice requirement of 15 days and are paid within 10 days of the end of the calendar month of the redemption request. (4) The investment is comprised of interests in multiple unrelated LP funds. The funds hold primarily long and short North American equities and target absolute returns using strategies designed to take advantage of market opportunities. The funds generally permit quarterly or semi-annual capital redemptions subject to notice requirements of 30 to 90 days . For some funds, redemptions above specified thresholds (lowest threshold is 90% ) may be only partially payable until after a fund audit is completed and are then payable within 30 days . (5) The investment is comprised of interests in multiple unrelated LP funds, each structured to provide capital appreciation through diversified investments in private equity, which can include investments in buyout, venture capital, debt including senior, second lien and mezzanine, distressed debt and other private equity-oriented LP s. Two of the LP s allow redemption by terms set forth in the LP agreements; the others do not permit redemption. Income and capital are to be periodically distributed at the discretion of the LP over time frames that are anticipated to span up to nine years. (6) This fund is a LLC structured to build and manage low volatility, multi-manager portfolios that have little or no correlation to the broader fixed income and equity security markets. Redemptions are not permitted but offers to repurchase units of the LLC may be extended periodically. (7) The investment is comprised of three unrelated LP funds. Two funds seek to obtain superior risk-adjusted absolute returns through a diversified portfolio of debt securities, including bonds, loans and other asset-backed instruments. The remaining fund seeks event driven opportunities across the corporate credit spectrum. Two funds are allowed redemptions at any quarter-end with a prior notice requirement of 90 days ; one fund permits redemption at any quarter-end with a prior notice requirement of 180 days . (8) This fund is a LLC invested across a broad range of commodities and focuses primarily on market neutral, relative value strategies, seeking to generate absolute returns with low correlation to broad commodity, equity and fixed income markets. Following an initial one-year lock-up period, redemptions are allowed with a prior notice requirement of 30 days and are payable within 30 days . (9) The investment is comprised of multiple unrelated LP s/ LLC s funds. One fund is a LLC focused on investing in North American consumer products companies, comprised of equity and equity-related securities, as well as debt instruments. Redemptions are not permitted. Another fund is a LP focused on North American energy infrastructure assets that allows redemption with consent of the General Partner. The remaining funds are real estate focused LP s, one of which allows for redemption with prior notice. ProAssurance may not sell, transfer or assign its interest in any of the above LP s/ LLC s without special consent from the LP s/ LLC s. Nonrecurring Fair Value Measurement At September 30, 2018 , ProAssurance did no t have any assets or liabilities that were measured at fair value on a nonrecurring basis. At December 31, 2017 , ProAssurance held an equity method early stage business investment measured at fair value on a nonrecurring basis due to a recognized OTTI of $8.5 million . The investment was valued using significant unobservable inputs (Level 3) and had a fair value of $1.2 million at December 31, 2017 . The fair value of the investment was measured as ProAssurance's ownership percentage in the projected earnings and cash flows expected to be generated by the investment. Financial Instruments - Methodologies Other Than Fair Value The following table provides the estimated fair value of our financial instruments that, in accordance with GAAP for the type of investment, are measured using a methodology other than fair value. All fair values provided primarily fall within the Level 3 fair value category. September 30, 2018 December 31, 2017 (In thousands) Carrying Fair Carrying Fair Financial assets: BOLI $ 63,638 $ 63,638 $ 62,113 $ 62,113 Other investments $ 2,930 $ 2,930 $ 58,546 $ 69,095 Other assets $ 38,405 $ 38,219 $ 34,020 $ 33,742 Financial liabilities: Senior notes due 2023* $ 250,000 $ 260,630 $ 250,000 $ 273,153 Revolving Credit Agreement* $ — $ — $ 123,000 $ 123,000 Mortgage loans* $ 39,413 $ 39,413 $ 40,460 $ 40,460 Other liabilities $ 23,186 $ 23,186 $ 21,154 $ 21,154 * Carrying value excludes debt issuance costs. The fair value of the BOLI was equal to the cash surrender value associated with the policies on the valuation date. Other investments listed in the table above include FHLB common stock carried at cost and an annuity investment carried at amortized cost. Two of ProAssurance's insurance subsidiaries are members of an FHLB . The estimated fair value of the FHLB common stock was based on the amount the subsidiaries would receive if their memberships were canceled, as the memberships cannot be sold. The fair value of the annuity represents the present value of the expected future cash flows discounted using a rate available in active markets for similarly structured instruments. Other assets and other liabilities primarily consisted of related investment assets and liabilities associated with funded deferred compensation agreements. The fair value of the funded deferred compensation assets was based upon quoted market prices, which is categorized as a Level 1 valuation, and had a fair value of $23.2 million and $20.2 million at September 30, 2018 and December 31, 2017 , respectively. The deferred compensation liabilities are adjusted to match the fair value of the deferred compensation assets. Other assets also included a secured note receivable and unsecured note receivable under two separate line of credit agreements. Fair value of these notes receivable was based on the present value of expected cash flows from the notes receivable, discounted at market rates on the valuation date for receivables with similar credit standings and similar payment structures. The fair value of the debt was estimated based on the present value of expected future cash outflows, discounted at rates available on the valuation date for similar debt issued by entities with a similar credit standing to ProAssurance.

Investments

Investments	9 Months Ended
	Sep. 30, 2018
Investments, Debt and Equity Securities [Abstract]
Investments	Investments Available-for-sale fixed maturities at September 30, 2018 and December 31, 2017 included the following: September 30, 2018 (In thousands) Amortized Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Fixed maturities, available for sale U.S. Treasury obligations $ 127,596 $ 164 $ 2,688 $ 125,072 U.S. Government-sponsored enterprise obligations 36,768 12 898 35,882 State and municipal bonds 308,712 3,900 2,424 310,188 Corporate debt 1,258,709 3,752 21,149 1,241,312 Residential mortgage-backed securities 192,859 793 6,192 187,460 Agency commercial mortgage-backed securities 13,893 — 349 13,544 Other commercial mortgage-backed securities 31,882 35 506 31,411 Other asset-backed securities 189,300 23 1,857 187,466 $ 2,159,719 $ 8,679 $ 36,063 $ 2,132,335 December 31, 2017 (In thousands) Amortized Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Fixed maturities, available for sale U.S. Treasury obligations $ 134,323 $ 485 $ 1,181 $ 133,627 U.S. Government-sponsored enterprise obligations 21,089 73 206 20,956 State and municipal bonds 618,414 14,248 419 632,243 Corporate debt 1,157,660 15,205 5,707 1,167,158 Residential mortgage-backed securities 196,741 2,438 1,335 197,844 Agency commercial mortgage-backed securities 10,827 23 108 10,742 Other commercial mortgage-backed securities 16,004 91 134 15,961 Other asset-backed securities 102,130 47 466 101,711 $ 2,257,188 $ 32,610 $ 9,556 $ 2,280,242 The recorded cost basis and estimated fair value of available-for-sale fixed maturities at September 30, 2018 , by contractual maturity, are shown below. Actual maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. (In thousands) Amortized Due in one Due after Due after Due after Total Fair Fixed maturities, available for sale U.S. Treasury obligations $ 127,596 $ 27,456 $ 76,463 $ 18,501 $ 2,652 $ 125,072 U.S. Government-sponsored enterprise obligations 36,768 3,276 12,973 19,502 131 35,882 State and municipal bonds 308,712 26,232 108,583 144,847 30,526 310,188 Corporate debt 1,258,709 144,784 714,013 352,691 29,824 1,241,312 Residential mortgage-backed securities 192,859 187,460 Agency commercial mortgage-backed securities 13,893 13,544 Other commercial mortgage-backed securities 31,882 31,411 Other asset-backed securities 189,300 187,466 $ 2,159,719 $ 2,132,335 Excluding obligations of the U.S. Government, U.S. Government-sponsored enterprises and a U.S. Government obligations money market fund, no investment in any entity or its affiliates exceeded 10% of shareholders’ equity at September 30, 2018 . Cash and securities with a carrying value of $46.1 million at September 30, 2018 were on deposit with various state insurance departments to meet regulatory requirements. As a member of Lloyd's and a capital provider to Syndicate 1729 and Syndicate 6131 , which began active operations on January 1, 2018, ProAssurance is required to maintain capital at Lloyd's , referred to as FAL . ProAssurance's FAL investments at September 30, 2018 included available-for-sale fixed maturities with a fair value of $124.7 million and short-term investments with a fair value of approximately $0.7 million on deposit with Lloyd's in order to satisfy these FAL requirements. Investments Held in a Loss Position The following tables provide summarized information with respect to investments held in an unrealized loss position at September 30, 2018 and December 31, 2017 , including the length of time the investment had been held in a continuous unrealized loss position. September 30, 2018 Total Less than 12 months 12 months or longer Fair Unrealized Fair Unrealized Fair Unrealized (In thousands) Value Loss Value Loss Value Loss Fixed maturities, available for sale U.S. Treasury obligations $ 118,159 $ 2,688 $ 62,352 $ 1,020 $ 55,807 $ 1,668 U.S. Government-sponsored enterprise obligations 34,713 898 22,082 364 12,631 534 State and municipal bonds 134,549 2,424 125,853 2,135 8,696 289 Corporate debt 967,853 21,149 746,194 13,342 221,659 7,807 Residential mortgage-backed securities 167,145 6,192 92,516 2,348 74,629 3,844 Agency commercial mortgage-backed securities 13,544 349 9,416 105 4,128 244 Other commercial mortgage-backed securities 29,076 506 24,184 322 4,892 184 Other asset-backed securities 167,353 1,857 131,437 1,308 35,916 549 $ 1,632,392 $ 36,063 $ 1,214,034 $ 20,944 $ 418,358 $ 15,119 December 31, 2017 Total Less than 12 months 12 months or longer Fair Unrealized Fair Unrealized Fair Unrealized (In thousands) Value Loss Value Loss Value Loss Fixed maturities, available for sale U.S. Treasury obligations $ 110,788 $ 1,181 $ 67,135 $ 554 $ 43,653 $ 627 U.S. Government-sponsored enterprise obligations 17,032 206 10,182 64 6,850 142 State and municipal bonds 23,122 419 15,168 102 7,954 317 Corporate debt 487,578 5,707 365,541 2,730 122,037 2,977 Residential mortgage-backed securities 109,659 1,335 64,121 402 45,538 933 Agency commercial mortgage-backed securities 4,423 108 2,458 34 1,965 74 Other commercial mortgage-backed securities 12,878 134 7,939 82 4,939 52 Other asset-backed securities 85,358 466 70,924 346 14,434 120 $ 850,838 $ 9,556 $ 603,468 $ 4,314 $ 247,370 $ 5,242 As of September 30, 2018 , excluding U.S. Government or U.S. Government-sponsored enterprise obligations, there were 1,090 debt securities ( 52.2% of all available-for-sale fixed maturity securities held) in an unrealized loss position representing 571 issuers. The greatest and second greatest unrealized loss positions among those securities were approximately $0.5 million and $0.4 million , respectively. The securities were evaluated for OTTI as of September 30, 2018 . As of December 31, 2017 , excluding U.S. Government or U.S. Government-sponsored enterprise obligations, there were 629 debt securities ( 26.5% of all available-for-sale fixed maturity securities held) in an unrealized loss position representing 375 issuers. The greatest and second greatest unrealized loss positions among those securities were approximately $0.4 million and $0.3 million , respectively. The securities were evaluated for OTTI as of December 31, 2017 . Each quarter, ProAssurance performs a detailed analysis for the purpose of assessing whether any of the securities it holds in an unrealized loss position has suffered an OTTI . A detailed discussion of the factors considered in the assessment is included in Note 1 of the Notes to Consolidated Financial Statements included in ProAssurance's December 31, 2017 Form 10-K. Fixed maturity securities held in an unrealized loss position at September 30, 2018 , excluding asset-backed securities, have paid all scheduled contractual payments and are expected to continue doing so. Expected future cash flows of asset-backed securities, excluding those issued by GNMA , FNMA and FHLMC , held in an unrealized loss position were estimated as part of the September 30, 2018 OTTI evaluation using the most recently available six-month historical performance data for the collateral (loans) underlying the security or, if historical data was not available, sector based assumptions, and equaled or exceeded the current amortized cost basis of the security. Other information regarding sales and purchases of fixed maturity available-for-sale securities is as follows: Three Months Ended September 30 Nine Months Ended September 30 (In millions) 2018 2017 2018 2017 Proceeds from sales (exclusive of maturities and paydowns) $ 61.3 $ 74.1 $ 556.3 $ 309.6 Purchases $ 164.6 $ 90.6 $ 717.1 $ 449.7 Equity Investments ProAssurance's equity investments are carried at fair value with changes in fair value recognized in income as a component of net realized investment gains (losses) during the period of change. Equity investments on the Condensed Consolidated Balance Sheet as of September 30, 2018 primarily included stocks, bonds and investment funds. Short-term Investments ProAssurance's short-term investments, which have a maturity at purchase of one year or less, are primarily comprised of investments in U.S. treasury obligations, commercial paper and money market funds. Short-term investments are carried at fair value which approximates the cost of the securities due to their short-term nature. BOLI ProAssurance holds BOLI policies that are carried at the current cash surrender value of the policies (original cost $33 million ). All insured individuals were members of ProAssurance management at the time the policies were acquired. The primary purpose of the program is to offset future employee benefit expenses through earnings on the cash value of the policies. ProAssurance is the owner and beneficiary of these policies. Net Investment Income Net investment income by investment category was as follows: Three Months Ended Nine Months Ended (In thousands) 2018 2017 2018 2017 Fixed maturities $ 17,228 $ 18,924 $ 51,814 $ 57,885 Equities 5,687 4,495 15,553 12,437 Short-term investments, including Other 1,330 1,147 3,968 2,926 BOLI 621 620 1,525 1,517 Investment fees and expenses (1,600 ) (1,457 ) (5,183 ) (5,173 ) Net investment income $ 23,266 $ 23,729 $ 67,677 $ 69,592 Investment in Unconsolidated Subsidiaries ProAssurance's investment in unconsolidated subsidiaries were as follows: September 30, 2018 Carrying Value (In thousands) Percentage September 30, December 31, Qualified affordable housing project tax credit partnerships See below $ 70,217 $ 84,607 Other tax credit partnerships See below 4,414 6,118 All other investments, primarily investment fund LPs/LLCs See below 316,107 239,866 $ 390,738 $ 330,591 Qualified affordable housing project tax credit partnership interests held by ProAssurance generate investment returns by providing tax benefits to fund investors in the form of tax credits and project operating losses. The carrying value of these investments reflects ProAssurance's total commitments (both funded and unfunded) to the partnerships, less any amortization. ProAssurance's ownership percentage relative to two of the tax credit partnership interests is almost 100% ; these interests had a carrying value of $26.7 million at September 30, 2018 and $32.5 million at December 31, 2017 . ProAssurance's ownership percentage relative to the remaining tax credit partnership interests is less than 20% ; these interests had a carrying value of $43.5 million at September 30, 2018 and $52.1 million at December 31, 2017 . Since ProAssurance has the ability to exert influence over the partnerships but does not control them, all are accounted for using the equity method. See further discussion of the entities in which ProAssurance holds passive interests in Note 11 . Other tax credit partnerships are comprised entirely of investments in historic tax credit partnerships. The historic tax credit partnerships generate investment returns by providing benefits to fund investors in the form of tax credits, tax deductible project operating losses and positive cash flows. The carrying value of these investments reflects ProAssurance's total funded commitments less any amortization. ProAssurance's ownership percentage relative to the historic tax credit partnerships is almost 100% . Since ProAssurance has the ability to exert influence over the partnerships but does not control them, all are accounted for using the equity method. See further discussion of the entities in which ProAssurance holds passive interests in Note 11 . ProAssurance holds interests in investment fund LP s/ LLC s and other equity method investments and LP s/ LLC s which are not considered to be investment funds. ProAssurance's ownership percentage relative to one of the LP s/ LLC s is greater than 25%, which is expected to be reduced as the funds mature and other investors participate in the funds; these investments had a carrying value of $24.1 million at September 30, 2018 and $30.8 million at December 31, 2017 . ProAssurance's ownership percentage relative to the remaining investments and LP s/ LLC s is less than 25%; these interests had a carrying value of $292.0 million at September 30, 2018 and $209.1 million at December 31, 2017 . ProAssurance does not have the ability to exert control over any of these funds. Equity in Earnings (Loss) of Unconsolidated Subsidiaries Equity in earnings (loss) of unconsolidated subsidiaries included losses from qualified affordable housing project tax credit partnerships and historic tax credit partnerships. Losses recorded reflect ProAssurance's allocable portion of partnership operating losses. Tax credits reduce income tax expense in the period they are recognized. Losses recorded and tax credits recognized related to ProAssurance's tax credit partnership investments were as follows: Three Months Ended Nine Months Ended (In thousands) 2018 2017 2018 2017 Qualified affordable housing project tax credit partnerships Losses recorded $ 4,661 $ 3,442 $ 14,373 $ 10,713 Tax credits recognized $ 4,618 $ 4,608 $ 13,855 $ 13,833 Historic tax credit partnerships Losses recorded $ 1,394 $ 621 $ 4,776 $ 3,388 Tax credits recognized $ 570 $ 1,352 $ 1,925 $ 3,976 Net Realized Investment Gains (Losses) Realized investment gains and losses are recognized on the first-in, first-out basis. The following table provides detailed information regarding net realized investment gains (losses): Three Months Ended Nine Months Ended (In thousands) 2018 2017 2018 2017 Total OTTI losses: Corporate debt $ (86 ) $ — $ (490 ) $ (419 ) Portion of OTTI losses recognized in other comprehensive income before taxes: Corporate debt — — — 248 Net impairment losses recognized in earnings (86 ) — (490 ) (171 ) Gross realized gains, available-for-sale fixed maturities 690 1,724 5,592 4,323 Gross realized (losses), available-for-sale fixed maturities (1,400 ) (262 ) (5,172 ) (1,730 ) Net realized gains (losses), short-term investments — (1 ) — (1 ) Net realized gains (losses), trading fixed maturities (28 ) — (100 ) — Net realized gains (losses), equity investments 4,689 3,603 17,395 10,958 Net realized gains (losses), other investments 561 478 1,652 2,197 Change in unrealized holding gains (losses), trading fixed maturities (42 ) — (261 ) — Change in unrealized holding gains (losses), equity investments 7,996 2,182 (15,104 ) 2,606 Change in unrealized holding gains (losses), convertible securities, carried at fair value (260 ) 23 (1,126 ) 621 Other 253 2 265 7 Net realized investment gains (losses) $ 12,373 $ 7,749 $ 2,651 $ 18,810 ProAssurance recognized OTTI in earnings of $0.1 million and $0.5 million during the three and nine months ended September 30, 2018 , respectively, related to debt instruments from two issuers in the energy sector. ProAssurance did no t recognize any OTTI during the three months ended September 30, 2017 . During the nine months ended September 30, 2017 , ProAssurance recognized OTTI in earnings of $0.2 million and $0.2 million of non-credit OTTI in OCI , both of which related to corporate bonds. The following table presents a roll forward of cumulative credit losses recorded in earnings related to impaired debt securities for which a portion of the OTTI was recorded in OCI . Three Months Ended Nine Months Ended (In thousands) 2018 2017 2018 2017 Balance beginning of period $ 1,313 $ 1,313 $ 1,313 $ 1,158 Additional credit losses recognized during the period, related to securities for which: No OTTI has been previously recognized — — — 171 Reductions due to: Securities sold during the period (realized) (1,220 ) — (1,220 ) (16 ) Balance September 30 $ 93 $ 1,313 $ 93 $ 1,313

Retroactive Insurance Contracts

Retroactive Insurance Contracts	9 Months Ended
	Sep. 30, 2018
Insurance [Abstract]
Retroactive Insurance Contracts	Retroactive Insurance Contracts ProAssurance offers custom alternative risk solutions including loss portfolio transfers for large healthcare entities who, most commonly, are exiting a line of business, changing an insurance approach or simply preferring to transfer risk. A loss portfolio transfer is a form of retroactive insurance coverage as the Company is assuming and accepting an entity’s existing open and future claim liabilities through the transfer of the entity’s loss reserves. In the second quarter of 2018, ProAssurance entered into a loss portfolio transfer with a large healthcare organization. Per the agreement, ProAssurance will cover a specific inventory of existing claims as well as provide tail coverage. As the contract included both prospective (tail) coverage and retroactive coverage, ProAssurance bifurcated the provisions of the contract and accounted for each component separately. As of the contract effective date, ProAssurance recognized total net premiums written and earned of $26.6 million , comprised of $7.9 million of prospective coverage and $18.7 million of retroactive coverage, and total net losses and loss adjustment expenses of $25.4 million in the Condensed Consolidated Statements of Income and Comprehensive Income for the nine months ended September 30, 2018 . In addition, ProAssurance recorded a deferred gain of $0.6 million in the reserve for losses and loss adjustment expenses on the Condensed Consolidated Balance Sheet in the second quarter of 2018 representing the excess of premiums received over losses assumed related to the retroactive coverage which are amortized into earnings over the estimated claim payment period. Amortization of this deferred gain was insignificant for the three and nine months ended September 30, 2018 . For additional information regarding ProAssurance's accounting policy for retroactive insurance contracts, see Note 1 .

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes ProAssurance estimates its annual effective tax rate at the end of each quarterly reporting period and uses this estimated rate to record the provision for income taxes in the interim financial statements. The provision for income taxes is different from that which would be obtained by applying the statutory federal income tax rate to income before income taxes primarily because a portion of ProAssurance’s investment income is tax-exempt, and because ProAssurance utilizes tax credit benefits transferred from tax credit partnership investments. In addition, ProAssurance's provision for income taxes in 2018 was impacted by certain provisions of the TCJA , as discussed below. ProAssurance had a total liability for federal and U.K. income taxes of $2.1 million at September 30, 2018 and $8.0 million at December 31, 2017 , both carried as a part of other liabilities. The liability for unrecognized tax benefits, which is included in the total liability for federal and U.K. income taxes, was $5.1 million and $5.8 million at September 30, 2018 and December 31, 2017 , respectively, which included an accrued liability for interest of approximately $0.6 million and $0.5 million , respectively. Tax Cuts and Jobs Act The TCJA was signed into law on December 22, 2017 and contains several key provisions that impact the Company's business, including the reduction of the U.S. federal corporate tax rate from 35% to 21% effective January 1, 2018, the reduction in the amount of executive compensation that could qualify as a tax deduction, a minimum tax on payments made to related foreign entities and a change in how property and casualty taxpayers discount loss reserves. Effective January 1, 2018, the TCJA introduced a minimum tax on payments made to related foreign entities referred to as the BEAT . The BEAT is imposed by adding back into the U.S. tax base any base erosion payment made by the U.S. taxpayer to a related foreign entity and applying a minimum tax rate to this newly calculated modified taxable income. Base erosion payments represent any amount paid or accrued by the U.S. taxpayer to a related foreign entity for which a deduction is allowed. Premiums the Company cedes to the SPC s at its newly formed wholly owned Cayman Islands reinsurance subsidiary, Inova Re , do not fall within the scope of base erosion payments as the SPC s at Inova Re intend to elect to be taxed as U.S. taxpayers. However, premiums the Company cedes to any active SPC at its wholly owned Cayman Islands reinsurance subsidiary, Eastern Re , fall within the scope of base erosion payments and therefore could be significantly impacted by the BEAT . See further discussion on the Company’s new subsidiary, Inova Re , and its Cayman Islands SPC operations in Note 13 . Management has evaluated its exposure to the BEAT and has concluded that the Company’s expected outbound deductible payments to related foreign entities are below the threshold for application of the BEAT ; therefore, ProAssurance has not recognized any incremental tax expense for the BEAT provision of the TCJA for the three and nine months ended September 30, 2018 . ProAssurance was able to complete its accounting for all areas of the TCJA during the period of enactment except as described as follows: Provisional amount finalized during the third quarter of 2018 As noted in ProAssurance's December 31, 2017 Form 10-K, ProAssurance was able to make a reasonable estimate of the effects on its existing deferred tax asset balances at December 31, 2017 as it relates to the limitation on the future deductibility of certain executive compensation and recorded a provisional charge to income tax expense from continuing operations for the year ended December 31, 2017 . During the third quarter of 2018, the IRS issued guidance addressing the effects of the TCJA on executive compensation; therefore, ProAssurance was able to complete its accounting for the impact of the TCJA on the ProAssurance's December 31, 2017 deferred tax asset balances related to executive compensation. As a result, ProAssurance did not record any measurement-period adjustments to the previously recorded provisional amount. Provisional amount not reasonably estimable As noted in ProAssurance's December 31, 2017 Form 10-K, ProAssurance was unable to reasonably estimate the impact of the change in loss reserve discounting factors due to the TCJA ; therefore, no provisional amount was recorded at December 31, 2017 . As of September 30, 2018 , the IRS has yet to release the 2018 discount factors; therefore, ProAssurance has not adjusted its deferred tax balances due to the enactment of the TCJA . ProAssurance continues to utilize the discount factors based on existing accounting guidance and the provisions of the tax laws that were in effect immediately prior to enactment of the TCJA . Once the IRS releases the 2018 loss reserve discount factors, ProAssurance will complete its analysis and include the effect of the difference in the reserve discount factors in the period the analysis is complete or the impact is reasonably estimable.

Reserve for Losses and Loss Adj

Reserve for Losses and Loss Adjustment Expenses	9 Months Ended
	Sep. 30, 2018
Insurance [Abstract]
Reserve for Losses and Loss Adjustment Expenses	Reserve for Losses and Loss Adjustment Expenses The reserve for losses is established based on estimates of individual claims and actuarially determined estimates of future losses based on ProAssurance’s past loss experience, available industry data and projections as to future claims frequency, severity, inflationary trends and settlement patterns. Estimating the reserve, particularly the reserve appropriate for liability exposures, is a complex process. Claims may be resolved over an extended period of time, often five years or more, and may be subject to litigation. Estimating losses requires ProAssurance to make and revise judgments and assessments regarding multiple uncertainties over an extended period of time. As a result, the reserve estimate may vary considerably from the eventual outcome. The assumptions used in establishing ProAssurance’s reserve are regularly reviewed and updated by management as new data becomes available. Changes to estimates of previously established reserves are included in earnings in the period in which the estimate is changed. ProAssurance believes that the methods it uses to establish reserves are reasonable and appropriate. Each year, ProAssurance uses internal actuaries to review the reserve for losses of each insurance subsidiary. ProAssurance also engages consulting actuaries to review ProAssurance claims data and provide observations regarding cost trends, rate adequacy and ultimate loss costs. ProAssurance considers the views of the actuaries as well as other factors, such as known, anticipated or estimated changes in frequency and severity of claims, loss retention levels and premium rates, in establishing the amount of its reserve for losses. The statutory filings of each insurance company with the insurance regulators must be accompanied by a consulting actuary's certification as to their respective reserves. ProAssurance partitions its reserve by accident year, which is the year in which the claim becomes its liability. As claims are incurred (reported) and claim payments are made, they are aggregated by accident year for analysis purposes. ProAssurance also partitions its reserve by reserve type: case reserves and IBNR reserves. Case reserves are established by the claims department based upon the particular circumstances of each reported claim and represent ProAssurance’s estimate of the future loss costs (often referred to as expected losses) that will be paid on reported claims. Case reserves are decremented as claim payments are made and are periodically adjusted upward or downward as estimates regarding the amount of future losses are revised; a reported loss for an individual claim equates to the case reserve at any point in time plus the claim payments that have been made to date. IBNR reserves represent an estimate, in the aggregate, of future development on losses that have been reported to ProAssurance plus an estimate of losses that have been incurred but not reported. Development of Prior Accident Years In addition to setting the initial reserve for the current accident year, each period ProAssurance reassesses the amount of reserve required for prior accident years. The foundation of ProAssurance’s reserve re-estimation process is an actuarial analysis that is performed by both the internal and consulting actuaries. This detailed analysis projects ultimate losses based on partitions which include line of business, geography, coverage layer and accident year. The procedure uses the most representative data for each partition, capturing its unique patterns of development and trends. In all, there are 200 different partitions of ProAssurance's business for purposes of this analysis. ProAssurance believes that the use of consulting actuaries provides an independent view of the loss data as well as a broader perspective on industry loss trends. Activity in the reserve for losses and loss adjustment expenses is summarized as follows: (In thousands) Nine Months Ended September 30, 2018 Nine Months Ended September 30, 2017 Year Ended December 31, 2017 Balance, beginning of year $ 2,048,381 $ 1,993,428 $ 1,993,428 Less reinsurance recoverables on unpaid losses and loss adjustment expenses 335,585 273,475 273,475 Net balance, beginning of year 1,712,796 1,719,953 1,719,953 Net losses: Current year* 506,269 454,121 603,518 Favorable development of reserves established in prior years, net (67,149 ) (90,063 ) (134,360 ) Total 439,120 364,058 469,158 Paid related to: Current year (69,881 ) (63,667 ) (106,633 ) Prior years (314,763 ) (293,522 ) (369,682 ) Total paid (384,644 ) (357,189 ) (476,315 ) Net balance, end of period 1,767,272 1,726,822 1,712,796 Plus reinsurance recoverables on unpaid losses and loss adjustment expenses 332,555 313,876 335,585 Balance, end of period $ 2,099,827 $ 2,040,698 $ 2,048,381 * Current year net losses during the 2018 nine-month period included incurred losses of $25.4 million related to a loss portfolio transfer entered into during the second quarter of 2018 (see Note 4). The favorable loss development of $67.1 million recognized in the nine months ended September 30, 2018 primarily reflected a lower than anticipated claims severity trend (i.e., the average size of a claim) for accident years 2011 through 2015 . The favorable loss development of $90.1 million recognized in the nine months ended September 30, 2017 primarily reflected a lower than anticipated claims severity trend for accident years 2010 through 2014 . The favorable loss development of $134.4 million recognized in the twelve months ended December 31, 2017 primarily reflected a lower than anticipated claims severity trend for accident years 2010 through 2014. For additional information regarding ProAssurance's reserve for losses, see Note 1 and Note 7 of the Notes to Consolidated Financial Statements included in ProAssurance's December 31, 2017 Form 10-K.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies ProAssurance is involved in various legal actions related to insurance policies and claims handling including, but not limited to, claims asserted by policyholders. These types of legal actions arise in the Company's ordinary course of business and, in accordance with GAAP for insurance entities, are considered as a part of the Company's loss reserving process, which is described in detail under the heading "Losses and Loss Adjustment Expenses" in the Accounting Policies section in Note 1 of the Notes to Consolidated Financial Statements in ProAssurance's 2017 Form 10-K. As a member of Lloyd's , ProAssurance is required to provide capital to support its Lloyd's Syndicates through 2022 of up to $200 million , referred to as FAL . At September 30, 2018 , ProAssurance is satisfying the FAL requirement with investment securities on deposit with Lloyd's with a carrying value of $125.4 million (see Note 3 ). ProAssurance has issued an unconditional revolving credit agreement to the Premium Trust Fund of Syndicate 1729 for the purpose of providing working capital. Permitted borrowings were expanded from £20.0 million to £30.0 million under an amended Syndicate Credit Agreement executed in February 2018. Under the amended Syndicate Credit Agreement , advances bear interest at 3.8% annually and may be repaid at any time but are repayable upon demand after December 31, 2019 . As of September 30, 2018 , the unused commitment under the Syndicate Credit Agreement approximated £8.8 million (approximately $11.5 million ). On occasion, ProAssurance has entered into financial instrument transactions that may present off-balance sheet credit risk or market risk. These transactions include a short-term loan commitment and commitments to provide funding to non-public investment entities. Under the short-term loan commitment, ProAssurance has agreed to advance funds on a 30 day basis to a counterparty provided there is no violation of any condition established in the contract. As of September 30, 2018 , ProAssurance had total funding commitments of approximately $272.1 million which primarily represented funding commitments related to non-public investment entities as well as a short-term loan commitment which included the amount at risk if the full short-term loan is extended and the counterparties default. However, the credit risk associated with the short-term loan commitment is minimal as the counterparties to the contract are highly rated commercial institutions and to-date have been performing in accordance with their contractual obligations.

Debt

Debt	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Debt	Debt ProAssurance’s outstanding debt consisted of the following: (In thousands) September 30, December 31, Senior Notes due 2023, unsecured, interest at 5.3% annually $ 250,000 $ 250,000 Revolving Credit Agreement, outstanding borrowings were fully secured and carried at a weighted average interest rate of 1.91%. Outstanding borrowings are not permitted to exceed $250 million aggregately; Revolving Credit Agreement expires in 2020. The interest rate on borrowings is set at the time the respective borrowing is initiated or renewed. — 123,000 Mortgage Loans, outstanding borrowings are secured by first priority liens on two office buildings, and bear an interest rate of three-month LIBOR plus 1.325% (3.66% and 2.86%, respectively) determined on a quarterly basis. 39,413 40,460 Total principal 289,413 413,460 Less debt issuance costs 1,399 1,649 Debt less debt issuance costs $ 288,014 $ 411,811 Covenant Compliance There are no financial covenants associated with the Senior Notes due 2023. The Revolving Credit Agreement contains customary representations, covenants and events constituting default, and remedies for default. The Revolving Credit Agreement also defines financial covenants regarding permitted leverage ratios. ProAssurance is currently in compliance with all covenants of the Revolving Credit Agreement . The Mortgage Loans contain customary representations, covenants and events constituting default, and remedies for default. The Mortgage Loans also define a financial covenant regarding a permitted leverage ratio for each of the two ProAssurance subsidiaries that entered into the Mortgage Loans. ProAssurance's subsidiaries are currently in compliance with the financial covenant of the Mortgage Loans. Additional Information For additional information regarding ProAssurance's debt, see Note 9 of the Notes to Consolidated Financial Statements included in ProAssurance's December 31, 2017 Form 10-K.

Derivatives

Derivatives	9 Months Ended
	Sep. 30, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives	Derivatives ProAssurance is exposed to certain risks relating to its ongoing business and investment activities. ProAssurance utilizes derivative instruments as part of its risk management strategy to reduce the market risk related to fluctuations in future interest rates associated with a portion of its variable-rate debt. As of September 30, 2018 , ProAssurance has not designated any derivative instruments as hedging instruments and does not use derivative instruments for trading purposes. ProAssurance utilizes an interest rate cap agreement with the objective of reducing the Company's exposure to interest rate risk related to its variable-rate Mortgage Loans. Additional information regarding the Company's Mortgage Loans is provided in Note 8 . Under the terms of the interest rate cap agreement, ProAssurance paid a premium of $2 million in the fourth quarter of 2017 for the right to receive cash payments based upon a notional amount of $35 million if and when the three-month LIBOR rises above 2.35% . The Company's variable-rate Mortgage Loans bear an interest rate of three-month LIBOR plus 1.325% . Therefore, this derivative instrument is effectively ensuring the interest rate related to the Mortgage Loans is capped at a maximum of 3.675% until expiration of the interest rate cap agreement in October 2027 . ProAssurance has designated the interest rate cap as an economic hedge (non-hedging instrument) of interest rate exposure and any change in fair value of the derivative is immediately recognized in earnings during the period of change. The following table provides a summary of the volume and fair value position of the interest rate cap as well as the reporting location in the Condensed Consolidated Balance Sheets as of September 30, 2018 and December 31, 2017 . ($ in thousands) September 30, 2018 December 31, 2017 Derivatives Not Designated as Hedging Instruments Location in the Condensed Consolidated Balance Sheets Number of Instruments Notional Amount (1) Estimated Fair Value (2) Number of Instruments Notional Amount (1) Estimated Fair Value (2) Interest Rate Cap Other assets 1 $ 35,000 $ 2,852 1 $ 35,000 $ 1,731 (1) Volume is represented by the derivative instrument's notional amount. (2) Additional information regarding the fair value of the Company's interest rate cap is provided in Note 2. The following table presents the pre-tax impact of the change in the fair value of the interest rate cap and the reporting location in the Condensed Consolidated Statements of Income and Comprehensive Income for the three and nine months ended September 30, 2018 and 2017 . Gains (Losses) Recognized in Income on Derivatives (In thousands) Three Months Ended September 30 Nine Months Ended September 30 Derivatives Not Designated as Hedging Instruments Location in the Condensed Consolidated Statements of Income and Comprehensive Income 2018 2017 2018 2017 Interest Rate Cap Interest expense $ 264 $ — $ 1,121 $ — As a result of this derivative instrument, ProAssurance is exposed to risk that the counterparty will fail to meet its contractual obligations. To mitigate this counterparty credit risk, ProAssurance only enters into derivative contracts with carefully selected major financial institutions based upon their credit ratings and monitors their creditworthiness. As of September 30, 2018 , the counterparty had an investment grade rating of BBB- and has performed in accordance with their contractual obligations.

Shareholders' Equity

Shareholders' Equity	9 Months Ended
	Sep. 30, 2018
Equity [Abstract]
Shareholders' Equity	Shareholders’ Equity At September 30, 2018 and December 31, 2017 , ProAssurance had 100 million shares of authorized common stock and 50 million shares of authorized preferred stock. The Board has the authority to determine provisions for the issuance of preferred shares, including the number of shares to be issued, the designations, powers, preferences and rights, and the qualifications, limitations or restrictions of such shares. To date, the Board has not approved the issuance of preferred stock. ProAssurance declared cash dividends of $0.31 per share during each of the first three quarters of both 2018 and 2017 , totaling $50.9 million and $49.6 million , for each respective nine-month period. At September 30, 2018 , Board authorizations for the repurchase of common shares or the retirement of outstanding debt of $109.6 million remained available for use. ProAssurance did no t repurchase any common shares during the nine months ended September 30, 2018 and 2017 . Share-based compensation expense and related tax benefits were as follows: Three Months Ended September 30 Nine Months Ended September 30 (In thousands) 2018 2017 2018 2017 Share-based compensation expense $ 1,628 $ 1,018 $ 4,145 $ 7,110 Related tax benefits $ 342 $ 356 $ 870 $ 2,489 ProAssurance awarded approximately 85,800 restricted share units and 27,200 base performance share units to employees in February 2018 . The fair value of each unit awarded was estimated at $44.73 , equal to the market value of a ProAssurance common share on the date of grant less the estimated present value of dividends during the vesting period. The majority of awards are charged to expense as an increase to additional paid-in capital over the service period (generally the vesting period) associated with the award. However, a nominal amount of awards are recorded as a liability as they are structured to be settled in cash. Restricted share units and performance share units vest in their entirety at the end of a three -year period following the grant date based on a continuous service requirement and, for performance share units, achievement of a performance objective. Partial vesting is permitted for retirees. For equity classified awards, a ProAssurance common share is issued for each unit once vesting requirements are met, except that units sufficient to satisfy required tax withholdings are paid in cash. The number of common shares issued for performance share units varies from 50% to 200% of base awards depending upon the degree to which stated performance objectives are achieved. ProAssurance issued approximately 52,800 and 80,600 common shares to employees in February 2018 related to restricted share units and performance share units, respectively, granted in 2015. Performance share units for the 2015 award were issued at a level of 125% . Liability classified awards, which are nominal in amount, are settled in cash at the end of the vesting period. ProAssurance issued approximately 2,500 common shares to employees in February 2018 as bonus compensation, as approved by the Compensation Committee of the Board. The shares issued were valued at fair value (the market price of a ProAssurance common share on the date of award). Other Comprehensive Income (Loss) and Accumulated Other Comprehensive Income (Loss) For the three and nine months ended September 30, 2018 and 2017 , OCI was almost entirely comprised of unrealized gains and losses, including non-credit impairment losses, arising during the period related to fixed maturity available-for-sale securities, less reclassification adjustments, as shown in the table that follows, net of tax. For the three and nine months ended September 30, 2018 and 2017 , OCI included changes related to the reestimation of the defined benefit plan liability assumed in the Eastern acquisition which were nominal in amount. The defined benefit plan is frozen as to the earnings of additional benefits and the benefit plan liability is reestimated annually. At September 30, 2018 and December 31, 2017 , AOCI was almost entirely comprised of accumulated unrealized gains and losses from fixed maturity available-for-sale securities, including accumulated non-credit impairments recognized through OCI of $0.1 million and $0.5 million , respectively, net of tax. At September 30, 2018 and December 31, 2017 , accumulated changes in the defined benefit plan liability not yet recognized in earnings were nominal in amount. Due to the adoption of accounting guidance in the first quarter of 2018 related to certain impacts of the TCJA , ProAssurance increased AOCI by approximately $3.4 million with a corresponding decrease to retained earnings of the same amount as of the beginning of 2018. See Note 1 for additional information on accounting guidance adopted during the period. At September 30, 2018 and December 31, 2017 , tax effects were computed using the enacted federal corporate tax rate of 21% and 35% , respectively, with the exception of unrealized gains and losses on available-for-sale securities held at our U.K. and Cayman Islands entities which in both periods were immaterial in amount. Amounts reclassified from AOCI to net income and the amounts of deferred tax expense (benefit) included in OCI were as follows: Three Months Ended September 30 Nine Months Ended September 30 (In thousands) 2018 2017 2018 2017 Reclassifications from AOCI to net income: Realized investment gains (losses) $ (175 ) $ 1,462 $ 551 $ 2,425 Non-credit impairment losses reclassified to earnings, due to sale of securities or reclassification as a credit loss (621 ) — (621 ) (3 ) Total gains (losses) reclassified, before tax effect (796 ) 1,462 (70 ) 2,422 Tax effect* 167 (512 ) 15 (848 ) Net reclassification adjustments $ (629 ) $ 950 $ (55 ) $ 1,574 Deferred tax expense (benefit) included in OCI $ (1,197 ) $ (373 ) $ (10,442 ) $ 4,091 * Tax effects were computed using a 21% and 35% rate for the three and nine months ended September 30, 2018 and 2017, respectively.

Variable Interest Entities

Variable Interest Entities	9 Months Ended
	Sep. 30, 2018
Variable Interest Entities [Abstract]
Variable Interest Entities	Variable Interest Entities ProAssurance holds passive interests in a number of entities that are considered to be VIE s under GAAP guidance. ProAssurance's VIE interests principally consist of interests in LP s/ LLC s formed for the purpose of achieving diversified equity and debt returns. At September 30, 2018 , ProAssurance's VIE interests totaled $304.7 million carried as a part of investment in unconsolidated subsidiaries. ProAssurance does not have power over the activities that most significantly impact the economic performance of these VIE s and thus is not the primary beneficiary. Therefore, ProAssurance has not consolidated these VIE s. ProAssurance’s involvement with each VIE is limited to its direct ownership interest in the VIE . Except for the funding commitments disclosed in Note 7 , ProAssurance has no arrangements with any of the VIE s to provide other financial support to or on behalf of the VIE . At September 30, 2018 , ProAssurance’s maximum loss exposure relative to these investments was limited to the carrying value of ProAssurance’s investment in the VIE .

Earnings Per Share

Earnings Per Share	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Earnings Per Share	Earnings Per Share Diluted weighted average shares is calculated as basic weighted average shares plus the effect, calculated using the treasury stock method, of assuming that restricted share units, performance share units and purchase match units have vested. The following table provides the weighted average number of common shares outstanding used in the calculation of the Company's basic and diluted earnings per share: (In thousands, except per share data) Three Months Ended September 30 Nine Months Ended September 30 2018 2017 2018 2017 Weighted average number of common shares outstanding, basic 53,620 53,413 53,585 53,377 Dilutive effect of securities: Restricted Share Units 83 87 78 81 Performance Share Units 48 88 52 105 Purchase Match Units 22 26 20 23 Weighted average number of common shares outstanding, diluted 53,773 53,614 53,735 53,586 Effect of dilutive shares on earnings per share $ — $ — $ — $ — All dilutive common share equivalents are reflected in the earnings per share calculation while antidilutive common share equivalents are not reflected in the earnings per share calculation. There were no antidilutive common share equivalents for the three months ended September 30, 2018 . The diluted weighted average number of common shares outstanding for the nine months ended September 30, 2018 excludes approximately 3,000 common share equivalents issuable under the Company's stock compensation plans, while the three and nine months ended September 30, 2017 periods exclude 28,000 and 9,000 common share equivalents, respectively, as their effect would be antidilutive.

Segment Information

Segment Information	9 Months Ended
	Sep. 30, 2018
Segment Reporting [Abstract]
Segment Information	Segment Information ProAssurance's segments are based on the Company's internal management reporting structure for which financial results are regularly evaluated by the Company's CODM to determine resource allocation and assess operating performance. The Company continually assesses its internal management reporting structure and information evaluated by the CODM to determine whether any changes have occurred that would impact its segment reporting structure. Segment Reorganization During the third quarter of 2018, ProAssurance altered its internal management reporting structure and the financial results evaluated by its CODM ; therefore, ProAssurance changed its operating segments to align with how the CODM currently oversees the business, allocates resources and evaluates operating performance. As a result of the segment reorganization, ProAssurance added an operating and reportable segment: Segregated Portfolio Cell Reinsurance. The Segregated Portfolio Cell Reinsurance segment provides the operating results of SPC s that assume workers’ compensation insurance, healthcare professional liability insurance or a combination of the two. The underwriting results of the SPC s that assume workers’ compensation business and healthcare professional liability business were previously reported in the Company's Workers’ Compensation and Specialty P&C segments, respectively, and the results of investment assets solely allocated to SPC operations, previously reported in the Company's Corporate segment, are now reported in the Segregated Portfolio Cell Reinsurance segment. The Workers' Compensation segment has also been renamed "Workers' Compensation Insurance." All prior period segment information has been recast to conform to the current period presentation. The segment reorganization had no impact on previously reported consolidated financial results. Descriptions of ProAssurance's five operating and reportable segments are as follows: Specialty P&C is primarily focused on professional liability insurance and medical technology liability insurance. Professional liability insurance is primarily offered to healthcare providers and institutions and to attorneys and their firms. Medical technology liability insurance is offered to medical technology and life sciences companies that manufacture or distribute products including entities conducting human clinical trials. Prior to 2018, the Specialty P&C segment ceded certain premium to the Lloyd's Syndicates segment under a quota share agreement with Syndicate 1729 ; however, this agreement was not renewed on January 1, 2018. As discussed below, the Lloyd's Syndicates segment results are typically reported on a quarter delay. For consistency purposes, results from this ceding arrangement, other than cash receipts or disbursements, are reported within the Specialty P&C segment on the same one-quarter delay. Additionally, the Specialty P&C segment cedes healthcare professional liability business to certain SPCs in the Company's Segregated Portfolio Cell Reinsurance segment. Workers' Compensation Insurance provides workers' compensation products primarily to employers with 1,000 or fewer employees. The segment's products include guaranteed cost, policyholder dividend policies, retrospectively-rated policies, deductible polices and alternative market solutions. Alternative market products include program design, fronting, claims administration, risk management, SPC rental, asset management and SPC management services. Alternative market premiums are 100% ceded to either SPCs in the Company's Segregated Portfolio Cell Reinsurance segment or, to a limited extent, to captive insurers unaffiliated with ProAssurance. Segregated Portfolio Cell Reinsurance reflects the operating results (underwriting profit or loss, plus investment results) of SPC s at Eastern Re and Inova Re , the Company's Cayman Islands SPC operations. The SPCs assume workers' compensation insurance, healthcare professional liability insurance or a combination of the two from the Workers' Compensation Insurance and Specialty P&C segments. Each SPC is owned, fully or in part, by an agency, group or association and the operating results of the SPC s are due to the owners of that cell. ProAssurance participates to a varying degree in the results of selected SPC s. SPC operating results due to external cell owners are reflected as a SPC dividend expense in the Segregated Portfolio Cell Reinsurance segment and in ProAssurance's Condensed Consolidated Statements of Income and Comprehensive Income. In addition, the Segregated Portfolio Cell Reinsurance segment includes the SPC investment results as the investments are solely for the benefit of the cell participants and investment results due to external cell owners are reflected in the SPC dividend expense. The segment operating results reflects ProAssurance's share of the underwriting and investment results of the SPCs in which ProAssurance participates. During the first quarter of 2018, ProAssurance restructured its Cayman Islands SPC operations. Beginning in 2018, all new and renewing alternative market business previously ceded to the SPCs at Eastern Re , with the exception of one program, is now ceded to SPC s operated by a newly formed wholly owned Cayman Islands subsidiary, Inova Re . As part of the restructuring, all SPC s previously operated by Eastern Re , with the exception of one program, ceased assuming new and renewing business on or after January 1, 2018. The external cell owners' cumulative undistributed earnings and the results of all SPCs for the current period due to external cell owners continue to be reported as SPC dividends payable and SPC dividend expense, respectively. Lloyd's Syndicates includes operating results from ProAssurance's participation in Lloyd's of London Syndicate 1729 and Syndicate 6131 , which is a SPA that began writing business effective January 1, 2018. The results of this segment are normally reported on a quarter delay, except when information is available that is material to the current period. Furthermore, investment results associated with the majority of investment assets solely allocated to Lloyd's Syndicate operations and certain U.S. paid administrative expenses are reported concurrently as that information is available on an earlier time frame. Beginning in 2018, ProAssurance increased its participation in the operating results of Syndicate 1729 from 58% to 62% and began its 100% participation in the operating results of Syndicate 6131 ; however, due to the quarter delay these changes were not reflected in the Lloyd's Syndicates segment results until the second quarter of 2018. Syndicate 1729 underwrites risks over a wide range of property and casualty insurance and reinsurance lines in both the U.S. and international markets. Syndicate 6131 focuses on contingency and specialty property business, also within the U.S. and international markets. Corporate includes ProAssurance's investment operations, interest expense and U.S. income taxes, all of which are managed at the corporate level with the exception of investment assets solely allocated to either SPC operations or Lloyd's Syndicate operations, as previously discussed. The segment also includes non-premium revenues generated outside of the Company's insurance entities and corporate expenses. The accounting policies of the segments are the same as those described in Note 1 of the Notes to Consolidated Financial Statements in ProAssurance’s December 31, 2017 report on Form 10-K and Note 1 of the Notes to Condensed Consolidated Financial Statements. ProAssurance evaluates the performance of its Specialty P&C and Workers' Compensation Insurance segments based on before tax underwriting profit or loss, which excludes investment performance. ProAssurance evaluates the performance of its Segregated Portfolio Cell Reinsurance segment based on before tax operating profit or loss, which includes the investment performance of assets solely allocated to SPC operations. Performance of the Lloyd's Syndicates segment is evaluated based on underwriting profit or loss, plus investment results of investment assets solely allocated to Lloyd's Syndicate operations, net of U.K. income tax expense. Performance of the Corporate segment is evaluated based on the contribution made to consolidated after-tax results. ProAssurance accounts for inter-segment transactions as if the transactions were to third parties at current market prices. Assets are not allocated to segments because investments, other than the investments discussed above that are solely allocated to the Segregated Portfolio Cell Reinsurance and Lloyd's Syndicates segments, and other assets are not managed at the segment level. Financial results by segment were as follows: Three Months Ended September 30, 2018 (In thousands) Specialty P&C Workers' Compensation Insurance Segregated Portfolio Cell Reinsurance Lloyd's Syndicates Corporate Inter-segment Eliminations Consolidated Net premiums earned $ 120,789 $ 47,296 $ 18,963 $ 19,022 $ — $ — $ 206,070 Net investment income — — 371 783 22,112 — 23,266 Equity in earnings (loss) of unconsolidated subsidiaries — — — — 5,228 — 5,228 Net realized gains (losses) — — 1,397 (98 ) 11,074 — 12,373 Other income (expense) (1) 1,426 376 86 352 699 (551 ) 2,388 Net losses and loss adjustment expenses (98,363 ) (30,650 ) (8,560 ) (10,032 ) — — (147,605 ) Underwriting, policy acquisition and operating expenses (1) (27,931 ) (15,410 ) (5,516 ) (8,439 ) (5,053 ) 505 (61,844 ) Segregated portfolio cells dividend (expense) income — — (5,255 ) — — — (5,255 ) Interest expense — — — — (3,645 ) 46 (3,599 ) Income tax benefit (expense) — — — 361 (155 ) — 206 Segment operating results $ (4,079 ) $ 1,612 $ 1,486 $ 1,949 $ 30,260 $ — $ 31,228 Significant non-cash items: Depreciation and amortization, net of accretion $ 1,715 $ 959 $ 83 $ (2 ) $ 2,751 $ — $ 5,506 Nine Months Ended September 30, 2018 (In thousands) Specialty P&C Workers' Compensation Insurance Segregated Portfolio Cell Reinsurance Lloyd's Syndicates Corporate Inter-segment Eliminations Consolidated Net premiums earned $ 378,355 $ 135,230 $ 54,247 $ 48,987 $ — $ — $ 616,819 Net investment income — — 1,100 2,370 64,207 — 67,677 Equity in earnings (loss) of unconsolidated subsidiaries — — — — 12,247 — 12,247 Net realized gains (losses) — — 467 (404 ) 2,588 — 2,651 Other income (expense) (1) 3,945 1,828 176 247 2,737 (1,778 ) 7,155 Net losses and loss adjustment expenses (292,742 ) (87,794 ) (27,561 ) (31,023 ) — — (439,120 ) Underwriting, policy acquisition and operating expenses (1) (83,833 ) (41,545 ) (16,070 ) (23,745 ) (15,351 ) 1,732 (178,812 ) Segregated portfolio cells dividend (expense) income — — (9,787 ) — — — (9,787 ) Interest expense — — — — (11,308 ) 46 (11,262 ) Income tax benefit (expense) — — — 355 3,584 — 3,939 Segment operating results $ 5,725 $ 7,719 $ 2,572 $ (3,213 ) $ 58,704 $ — $ 71,507 Significant non-cash items: Depreciation and amortization, net of accretion $ 5,343 $ 2,873 $ 393 $ (5 ) $ 7,940 $ — $ 16,544 Three Months Ended September 30, 2017 (In thousands) Specialty P&C Workers' Compensation Insurance Segregated Portfolio Cell Reinsurance Lloyd's Syndicates Corporate Inter-segment Eliminations Consolidated Net premiums earned $ 117,288 $ 41,540 $ 17,157 $ 16,318 $ — $ — $ 192,303 Net investment income — — 290 412 23,027 — 23,729 Equity in earnings (loss) of unconsolidated subsidiaries — — — — 4,164 — 4,164 Net realized gains (losses) — — 944 31 6,774 — 7,749 Other income (expense) (1) 1,276 535 33 (1,881 ) 1,023 (476 ) 510 Net losses and loss adjustment expenses (72,944 ) (27,065 ) (8,903 ) (20,444 ) — — (129,356 ) Underwriting, policy acquisition and operating expenses (1) (26,816 ) (13,912 ) (5,147 ) (6,723 ) (4,989 ) 476 (57,111 ) Segregated portfolio cells dividend (expense) income — — (2,891 ) — — — (2,891 ) Interest expense — — — — (4,124 ) — (4,124 ) Income tax benefit (expense) — — — (61 ) (5,963 ) — (6,024 ) Segment operating results $ 18,804 $ 1,098 $ 1,483 $ (12,348 ) $ 19,912 $ — $ 28,949 Significant non-cash items: Depreciation and amortization, net of accretion $ 1,933 $ 848 $ 176 $ (6 ) $ 4,124 $ — $ 7,075 Nine Months Ended September 30, 2017 (In thousands) Specialty P&C Workers' Compensation Insurance Segregated Portfolio Cell Reinsurance Lloyd's Syndicates Corporate Inter-segment Eliminations Consolidated Net premiums earned $ 337,287 $ 122,247 $ 50,651 $ 45,374 $ — $ — $ 555,559 Net investment income — — 742 1,194 67,656 — 69,592 Equity in earnings (loss) of unconsolidated subsidiaries — — — — 8,489 — 8,489 Net realized gains (losses) — — 2,715 105 15,990 — 18,810 Other income (expense) (1) 3,943 1,716 83 (1,641 ) 1,974 (1,494 ) 4,581 Net losses and loss adjustment expenses (217,512 ) (79,520 ) (26,308 ) (40,718 ) — — (364,058 ) Underwriting, policy acquisition and operating expenses (1) (78,601 ) (38,912 ) (15,239 ) (19,786 ) (21,062 ) 1,494 (172,106 ) Segregated portfolio cells dividend (expense) income (2) (5,181 ) — (8,895 ) — — — (14,076 ) Interest expense — — — — (12,402 ) — (12,402 ) Income tax benefit (expense) (2) — — — 495 (4,962 ) — (4,467 ) Segment operating results $ 39,936 $ 5,531 $ 3,749 $ (14,977 ) $ 55,683 $ — $ 89,922 Significant non-cash items: Depreciation and amortization, net of accretion $ 5,350 $ 2,516 $ 500 $ (14 ) $ 12,672 $ — $ 21,024 (1) As a result of the third quarter 2018 segment reorganization, certain fees for services provided to the SPCs at Eastern Re and Inova Re are recorded as expenses within the Segregated Portfolio Cell Reinsurance segment and as other income within the Workers' Compensation Insurance segment. These fees are eliminated between segments in consolidation. These services primarily include SPC rental fees and were previously eliminated within the Company's Workers' Compensation segment. (2) During the second quarter of 2017, ProAssurance recognized a $5.2 million pre-tax expense related to previously unrecognized SPC dividend expense for the cumulative earnings of unrelated parties that have owned segregated portfolio cells at various periods since 2003 in a Bermuda captive insurance operation managed by the Company's HCPL line of business within the Specialty P&C segment. The expense recorded in the second quarter of 2017 related to periods prior to the then current period and was unrelated to the captive operations of the Company's Eastern Re subsidiary. The $1.8 million tax impact of the expense recognized in the second quarter of 2017 was included in the Corporate segment's income tax benefit (expense). The following table provides detailed information regarding ProAssurance's gross premiums earned by product as well as a reconciliation to net premiums earned. All gross premiums earned are from external customers except as noted. ProAssurance's insured risks are primarily within the U.S. Three Months Ended September 30 Nine Months Ended September 30 (In thousands) 2018 2017 2018 2017 Specialty P&C Segment Gross premiums earned: Healthcare professional liability $ 126,012 $ 125,377 $ 390,904 $ 358,209 Legal professional liability 6,606 6,483 19,486 19,217 Medical technology liability 9,080 8,459 26,372 25,160 Other 113 108 346 311 Ceded premiums earned (21,022 ) (23,139 ) (58,753 ) (65,610 ) Segment net premiums earned 120,789 117,288 378,355 337,287 Workers' Compensation Insurance Segment Gross premiums earned: Traditional business 50,271 43,734 145,334 128,203 Alternative market business 21,564 20,200 61,593 59,855 Ceded premiums earned (24,539 ) (22,394 ) (71,697 ) (65,811 ) Segment net premiums earned 47,296 41,540 135,230 122,247 Segregated Portfolio Cell Reinsurance Segment Gross premiums earned: Workers' compensation (1) 20,251 18,296 57,287 54,016 Healthcare professional liability (2) 1,225 1,044 3,782 3,106 Ceded premiums earned (2,513 ) (2,183 ) (6,822 ) (6,471 ) Segment net premiums earned 18,963 17,157 54,247 50,651 Lloyd's Syndicates Segment Gross premiums earned: Property and casualty (3) 23,050 18,790 60,289 52,935 Ceded premiums earned (4,028 ) (2,472 ) (11,302 ) (7,561 ) Segment net premiums earned 19,022 16,318 48,987 45,374 Consolidated net premiums earned $ 206,070 $ 192,303 $ 616,819 $ 555,559 (1) Premium for all periods is assumed from the Workers' Compensation Insurance segment. (2) Premium for all periods is assumed from the Specialty P&C segment. (3) Includes premium assumed from the Specialty P&C segment of $1.2 million and $4.5 million for the three and nine months ended September 30, 2018 , respectively, and $2.9 million and $9.5 million for the same respective periods of 2017 .

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2018
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events In October 2018, ProAssurance entered into an agreement with a company to provide data analytics services for certain product lines within the Company's HCPL book of business. The agreement contains a minimum two year commitment with optional extension features for an annual fee of approximately $5 million per year with additional variable quarterly incentive fees based on service utilization metrics prescribed in the contract.

Basis of Presentation (Policies

Basis of Presentation (Policies)	9 Months Ended
	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited Condensed Consolidated Financial Statements include the accounts of ProAssurance Corporation and its consolidated subsidiaries (ProAssurance, PRA or the Company). The financial statements have been prepared in accordance with GAAP for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and notes required by GAAP for complete financial statements. In the opinion of management, all adjustments considered necessary for a fair presentation, consisting of normal recurring adjustments, have been included. ProAssurance’s results for the nine months ended September 30, 2018 are not necessarily indicative of the results that may be expected for the year ending December 31, 2018 . The accompanying Condensed Consolidated Financial Statements should be read in conjunction with the Consolidated Financial Statements and Notes contained in ProAssurance’s December 31, 2017 report on Form 10-K. In connection with its preparation of the Condensed Consolidated Financial Statements, ProAssurance evaluated events that occurred subsequent to September 30, 2018 for recognition or disclosure in its financial statements and notes to financial statements. Beginning in the third quarter of 2018, ProAssurance operates in five reportable segments as follows: Specialty P&C , Workers' Compensation Insurance, Segregated Portfolio Cell Reinsurance, Lloyd's Syndicates and Corporate. For more information on the Company's segment reporting, including the nature of products and services provided and financial information by segment, refer to Note 13 .
Reclassifications	Reclassifications As a result of the third quarter 2018 segment reorganization, prior period segment information in Note 13 has been recast to conform to the Company's current segment reporting (see Note 13 for further information). Certain other insignificant prior period amounts have been reclassified to conform to the current period presentation.
Retroactive Insurance Contracts	Retroactive Insurance Contracts In certain instances, ProAssurance’s insurance contracts cover losses both on a prospective basis and retroactive basis and, accordingly, ProAssurance bifurcates the prospective and retroactive provisions of these contracts and accounts for each component separately, where practicable. The prospective provisions of a contract are accounted for consistently with the Company’s other insurance contracts as discussed in Note 1 of the Notes to Consolidated Financial Statements in ProAssurance’s December 31, 2017 report on Form 10-K. Under the retroactive provisions of a contract, all premiums received and losses assumed are recognized immediately in earnings at the inception of the contract as all of the underlying loss events occurred in the past. If the estimated losses assumed differ from the premium received related to the retroactive provision of a contract, the resulting difference is deferred and recognized over the estimated claim payment period with the periodic amortization reflected in earnings as a component of net losses and loss adjustment expenses. Deferred gains are included as a component of the reserve for losses and loss adjustment expenses and deferred losses are included as a component of other assets on the Condensed Consolidated Balance Sheet. Subsequent changes to the estimated timing or amount of future loss payments in relation to the losses assumed under retroactive provisions also produce changes in deferred balances. Changes in such estimates are applied retrospectively and the resulting changes in deferred balances, together with periodic amortization, are included in earnings in the period of change.
Accounting Changes Adopted and Not Yet Adopted	Accounting Changes Adopted Restricted Cash ( ASU 2016-18) Effective for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years, the FASB issued guidance related to the classification of restricted cash presented in the statement of cash flows with the objective of reducing diversity in practice. Under the new guidance, entities are required to include restricted cash and restricted cash equivalents with cash and cash equivalents when reconciling beginning-of-period and end-of-period total amounts as presented on the statement of cash flows. ProAssurance adopted the guidance as of January 1, 2018. Adoption of the guidance had no material effect on ProAssurance’s results of operations, financial position or cash flows. Intra-Entity Transfers of Assets Other than Inventory ( ASU 2016-16) Effective for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years, the FASB issued guidance which reduces the complexity in accounting standards related to the income tax consequences of intra-entity transfers of assets other than inventory between tax-paying components. A tax-paying component is an individual entity or group of entities that is consolidated for tax purposes. Under the new guidance, entities are required to recognize income tax consequences of an intra-entity transfer of assets other than inventory when the transfer occurs instead of delaying recognition until the asset has been sold to an outside party. ProAssurance adopted the guidance as of January 1, 2018. Adoption of the guidance had no material effect on ProAssurance’s results of operations, financial position or cash flows. Classification of Certain Cash Receipts and Cash Payments ( ASU 2016-15) Effective for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years, the FASB issued guidance related to the classification of certain cash receipts and cash payments presented in the statement of cash flows with the objective of reducing diversity in practice. ProAssurance adopted the guidance as of January 1, 2018 and elected to use the cumulative earnings approach for presenting distributions from equity method investees. Adoption of the guidance had no material effect on ProAssurance’s results of operations or financial position; however, ProAssurance reclassified approximately $20.2 million in distributions from unconsolidated subsidiaries from investing activities to operating activities in the Condensed Consolidated Statement of Cash Flows for the nine months ended September 30, 2017 . Revenue from Contracts with Customers ( ASU 2014-09) Effective for fiscal years beginning after December 15, 2017 the FASB issued guidance related to revenue from contracts with customers. The core principle of the new guidance is that revenue is recognized to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. ProAssurance adopted the guidance as of January 1, 2018 under the modified retrospective method. Adoption of the guidance had no material effect on ProAssurance’s results of operations, financial position or cash flows. Recognition and Measurement of Financial Assets and Financial Liabilities ( ASU 2016-01) Effective for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years, the FASB issued guidance that requires equity investments (except those accounted for under the equity method of accounting, or those that result in consolidation of the investee) to be measured at fair value with changes in fair value recognized in net income. The new guidance also specifies that an entity use the exit price notion when measuring the fair value of financial instruments for disclosure purposes and present financial assets and liabilities by measurement category and form of financial asset. Other provisions of the new guidance include: revised disclosure requirements related to the presentation in comprehensive income of changes in the fair value of liabilities; elimination, for public companies, of disclosure requirements relative to the methods and significant assumptions underlying fair values disclosed for financial instruments measured at amortized cost; and simplified impairment assessments for equity investments without readily determinable fair values. ProAssurance adopted the guidance as of January 1, 2018 using a modified retrospective application and recorded a cumulative-effect after-tax adjustment of approximately $8.3 million to beginning retained earnings in the Condensed Consolidated Statement of Changes in Capital for the nine months ended September 30, 2018 . LP s/ LLC s previously reported using the cost method are now reported at fair value with increases in fair value of approximately $5.2 million and $11.1 million recognized as a component of equity in earnings (loss) of unconsolidated subsidiaries on the Condensed Consolidated Statements of Income and Comprehensive Income for the three and nine months ended September 30, 2018 , respectively. Modification Accounting for Employee Share-Based Payment Awards ( ASU 2017-09) Effective for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years, the FASB issued guidance which reduces the complexity in accounting standards when there is a change in the terms or conditions of a share-based payment award. The new guidance clarifies that an entity should apply the modification accounting guidance if the value, vesting conditions or classification of the award changes. ProAssurance adopted the guidance as of January 1, 2018. Adoption of the guidance had no material effect on ProAssurance’s results of operations, financial position or cash flows. Reclassification of Certain Tax Effects from AOCI ( ASU 2018-02) Effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years, with early adoption permitted, the FASB issued guidance which permits a reclassification from AOCI to retained earnings for stranded tax effects resulting from the newly enacted federal corporate tax rate from the TCJA . The amount of the reclassification from AOCI to retained earnings will be the difference between the historical corporate tax rate and the newly enacted 21% corporate tax rate on deferred tax items originally established through OCI and not net income. The guidance allows entities to adopt in any interim or annual period for which financial statements have not yet been issued and apply the guidance either (1) in the period of adoption or (2) retrospectively to each period in which the effect of the change in the tax rate is recognized. ProAssurance adopted this guidance as of January 1, 2018 and elected to apply this guidance in the period of adoption using the specific identification method. Using a modified retrospective application, ProAssurance recorded a cumulative-effect adjustment which increased beginning AOCI by approximately $3.4 million and decreased beginning retained earnings by the same amount in the Condensed Consolidated Statement of Changes in Capital for the nine months ended September 30, 2018 . Adoption of this guidance had no material effect on ProAssurance's financial position, results of operations or cash flows. Technical Corrections and Improvements to Financial Instruments - Overall ( ASU 2018-03) Effective for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years beginning after June 15, 2018, the FASB amended the new standard on recognizing and measuring financial assets and financial liabilities to clarify certain aspects of the guidance. Under the amended guidance, an entity that uses the measurement alternative for equity investments without readily determinable fair values can change its measurement approach to a fair value method through an irrevocable election that would apply to that security and all identical or similar investments of the same issuer. Also, entities are required to use the prospective transition approach only for equity investments they elect to measure using the new measurement alternative. Additionally, the guidance clarifies how to apply the measurement alternative and presentation requirements for financial liabilities measured under the fair value option. ProAssurance adopted the guidance as of July 1, 2018 and adoption had no material effect on ProAssurance's financial position, results of operations or cash flows as ProAssurance does not have any equity investments without readily determinable fair values or financial liabilities measured under the fair value option. Accounting Changes Not Yet Adopted Leases ( ASU 2016-02) Effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years, the FASB issued guidance that requires a lessee to recognize for all leases (with the exception of short-term leases) a lease liability, which is a lessee's obligation to make lease payments arising from a lease, measured on a discounted basis, and a right-of-use asset, which is an asset that represents the lessee's right to use, or control the use of, a specified asset for the lease term. ProAssurance plans to adopt the guidance beginning January 1, 2019 using a modified retrospective application and plans to elect the transition option provided that allows companies to continue to apply legacy GAAP in comparative periods. As of September 30, 2018 , ProAssurance is currently in the process of evaluating all of its leases. As the majority of ProAssurance's leases are real estate operating leases and are not considered to be material, adoption of the guidance is not expected to have a material effect on ProAssurance’s results of operations, financial position or cash flows. In addition, ProAssurance's Revolving Credit Agreement contains a financial covenant regarding permitted leverage ratios based upon Consolidated Funded Indebtedness to Consolidated Total Capitalization; however, ProAssurance does not anticipate that the adoption of this guidance would have a material impact on the covenant. ProAssurance’s Mortgage Loans also contain a financial covenant regarding permitted leverage ratios, principally based upon SAP Consolidated Net Worth; however, as the NAIC is not anticipated to adopt the principles in the FASB guidance around capitalizing operating leases, adoption of the guidance would have no impact on the covenant. Premium Amortization on Purchased Callable Debt Securities ( ASU 2017-08) Effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years, the FASB issued guidance that will require the premium for certain callable debt securities to be amortized over a shorter period than is currently required. Currently amortization is permitted over the contractual life of the instrument and the guidance shortens the amortization to the earliest call date. The purpose of the guidance is to more closely align the amortization period of premiums to expectations incorporated in market pricing on the underlying securities. ProAssurance plans to adopt the guidance beginning January 1, 2019. As ProAssurance amortizes premium on callable debt securities to the earliest call date, adoption of the guidance is not expected to have a material effect on ProAssurance’s results of operations, financial position or cash flows. Derivatives and Hedging ( ASU 2017-12) Effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years, the FASB issued guidance to improve financial reporting of hedging relationships to better portray the entity's risk management activities in the consolidated financial statements. The new guidance eliminates the requirement to separately measure and report hedge ineffectiveness and requires the entire change in the fair value of a hedging instrument to be presented in the same income statement line as the hedged item. ProAssurance plans to adopt the guidance beginning January 1, 2019. ProAssurance's derivative instrument at September 30, 2018 is not designated as a hedging instrument; therefore, adoption is not expected to have a material effect on ProAssurance's results of operations, financial position or cash flows. Improvements to Nonemployee Share-Based Payment Accounting ( ASU 2018-07) Effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years, the FASB issued guidance which reduces the complexity in accounting for nonemployee share-based payment awards. The new guidance substantially aligns the accounting for nonemployee share-based payment awards with the accounting guidance for employee share-based payment awards with certain exceptions, including the inputs used in estimating the fair value of the nonemployee awards and the period of time and pattern of expense recognition. ProAssurance plans to adopt the guidance as of January 1, 2019. Adoption of the guidance is not expected to have a material effect on ProAssurance’s results of operations, financial position or cash flows. Improvements to Financial Instruments - Credit Losses ( ASU 2016-13) Effective for fiscal years beginning after December 15, 2019 and interim periods within those fiscal years, the FASB issued guidance that replaces the incurred loss impairment methodology, which delays recognition of credit losses until a probable loss has been incurred, with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. Under the new guidance, credit losses are required to be recorded through an allowance for credit losses account and the income statement reflects the measurement for newly recognized financial assets, as well as increases or decreases of expected credit losses that have taken place during the period. Credit losses on available-for-sale fixed maturity securities will be measured in a manner similar to current GAAP, although the new guidance requires that credit losses be presented as an allowance, rather than as a write-down of the asset, limited to the amount by which the fair value is below amortized cost. In addition, this guidance could impact ProAssurance's receivables from reinsurers; however, ProAssurance has not historically experienced material credit losses due to the financial condition of a reinsurer. ProAssurance plans to adopt the guidance beginning January 1, 2020 and is in the process of evaluating the effect the new guidance would have on its results of operations and financial position. Simplifying the Test for Goodwill Impairment ( ASU 2017-04) Effective for the fiscal years beginning after December 15, 2019 and interim periods within those fiscal years, the FASB issued guidance that simplifies the requirements to test goodwill for impairment for business entities that have goodwill reported in their financial statements. The guidance eliminates the second step of the impairment test which measures a goodwill impairment loss by comparing the implied fair value of a reporting unit's goodwill with the carrying amount. In addition, the guidance also eliminates the requirements for any reporting unit with a zero or negative carrying amount to perform a qualitative assessment. ProAssurance plans to adopt the guidance beginning January 1, 2020. Adoption is not expected to have a material effect on ProAssurance’s results of operations, financial position or cash flows. Changes to the Disclosure Requirements for Fair Value Measurement ( ASU 2018-13) Effective for fiscal years beginning after December 15, 2019 and interim periods within those fiscal years, the FASB issued guidance that eliminates, modifies and adds certain disclosure requirements related to fair value measurements. The new guidance eliminates the requirements to disclose the transfers between Level 1 and Level 2 of the fair value hierarchy, the policy for the timing of transfers between levels of the fair value hierarchy and the valuation process for Level 3 fair value measurements while it modifies existing disclosure requirements related to measurement uncertainty and the requirement to disclose the timing of liquidation of an investee's assets for investments in certain entities that calculate NAV . The new guidance also adds requirements to disclose changes in unrealized gains and losses included in OCI for recurring Level 3 fair value measurements as well as the range and weighted average used to develop significant unobservable inputs for Level 3 fair value measurements. An entity is permitted to early adopt any eliminated or modified disclosure requirements and delay adoption of the additional disclosure requirements until the guidance is effective. As of September 30, 2018 , ProAssurance has elected to early adopt the provisions that eliminate and modify certain disclosure requirements within Note 2 on a retrospective basis and adoption of these certain provisions had no material effect on ProAssurance’s results of operations, financial position or cash flows as it affected disclosures only. ProAssurance plans to adopt the additional disclosure requirements beginning January 1, 2020 and adoption is not expected to have a material effect on ProAssurance’s results of operations, financial position or cash flows. Intangibles - Goodwill and Other-Internal-Use Software ( ASU 2018-15) Effective for fiscal years beginning after December 15, 2019 and interim periods within those fiscal years, the FASB amended the new standard regarding accounting for implementation costs in cloud computing arrangements. The amended guidance substantially aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. ProAssurance plans to adopt the guidance beginning January 1, 2020. Adoption is not expected to have a material effect on ProAssurance’s results of operations, financial position or cash flows.
Fair Value Measurement	The fair values for securities included in the Level 2 category, with the few exceptions described below, were developed by one of several third party, nationally recognized pricing services, including services that price only certain types of securities. Each service uses complex methodologies to determine values for securities and subject the values they develop to quality control reviews. Management selected a primary source for each type of security in the portfolio and reviewed the values provided for reasonableness by comparing data to alternate pricing services and to available market and trade data. Values that appeared inconsistent were further reviewed for appropriateness. Any value that did not appear reasonable was discussed with the service that provided the value and adjusted, if necessary. There were no material changes to the values supplied by the pricing services during the three and nine months ended September 30, 2018 and 2017 . Level 2 Valuations Below is a summary description of the valuation methodologies primarily used by the pricing services for securities in the Level 2 category, by security type: U.S. Treasury obligations were valued based on quoted prices for identical assets, or, in markets that are not active, quotes for similar assets, taking into consideration adjustments for variations in contractual cash flows and yields to maturity. U.S. Government-sponsored enterprise obligations were valued using pricing models that consider current and historical market data, normal trading conventions, credit ratings, and the particular structure and characteristics of the security being valued, such as yield to maturity, redemption options, and contractual cash flows. Adjustments to model inputs or model results were included in the valuation process when necessary to reflect recent regulatory, government or corporate actions or significant economic, industry or geographic events affecting the security’s fair value. State and municipal bonds were valued using a series of matrices that considered credit ratings, the structure of the security, the sector in which the security falls, yields, and contractual cash flows. Valuations were further adjusted, when necessary, to reflect the expected effect on fair value of recent significant economic or geographic events or ratings changes. Corporate debt, multiple observable inputs consisted primarily of corporate bonds, but also included a small number of bank loans. The methodology used to value Level 2 corporate bonds was the same as the methodology previously described for U.S. Government-sponsored enterprise obligations. Bank loans were valued based on an average of broker quotes for the loans in question, if available. If quotes were not available, the loans were valued based on quoted prices for comparable loans or, if the loan was newly issued, by comparison to similar seasoned issues. Broker quotes were compared to actual trade prices to permit assessment of the reliability of the quotes; unreliable quotes were not considered in quoted averages. Residential and commercial mortgage-backed securities were valued using a pricing matrix which considers the issuer type, coupon rate and longest cash flows outstanding. The matrix used was based on the most recently available market information. Agency and non-agency collateralized mortgage obligations were both valued using models that consider the structure of the security, current and historical information regarding prepayment speeds, ratings and ratings updates, and current and historical interest rate and interest rate spread data. Other asset-backed securities were valued using models that consider the structure of the security, monthly payment information, current and historical information regarding prepayment speeds, ratings and ratings updates, and current and historical interest rate and interest rate spread data. Spreads and prepayment speeds consider collateral type. Short-term investments were securities maturing within one year, carried at fair value which approximated the cost of the securities due to their short-term nature. Other investments consisted primarily of convertible bonds valued using a pricing model that incorporated selected dealer quotes as well as current market data regarding equity prices and risk free rates. If dealer quotes were unavailable for the security being valued, quotes for securities with similar terms and credit status were used in the pricing model. Dealer quotes selected for use were those considered most accurate based on parameters such as underwriter status and historical reliability. Other assets consisted of an interest rate cap derivative instrument, which is discussed in Note 9 , valued using a model which considers the volatilities from other instruments with similar maturities, strike prices, durations and forward yield curves. Level 3 Valuations Below is a summary description of the valuation methodologies used as well as quantitative information regarding securities in the Level 3 category, by security type: Level 3 Valuation Methodologies Corporate debt, limited observable inputs consisted of corporate bonds valued using dealer quotes for similar securities or discounted cash flow models using yields currently available for similar securities. Similar securities are defined as securities of comparable credit quality that have like terms and payment features. Assessments of credit quality were based on NRSRO ratings, if available, or were subjectively determined by management if not available. At September 30, 2018 , 79% of the securities were rated and the average rating was BBB+ . At December 31, 2017 , 84% of the securities were rated and the average rating was BBB+ . Residential mortgage-backed and other asset-backed securities consisted of securitizations of receivables valued using dealer quotes for similar securities or discounted cash flow models using yields currently available for similar securities. Similar securities are defined as securities of comparable credit quality that have like terms and payment features. Assessments of credit quality were based on NRSRO ratings, if available, or were subjectively determined by management if not available. At September 30, 2018 , 60% of the securities were rated and the average rating was AAA . At December 31, 2017 , 21% of the securities were rated and the average rating was AAA . Other investments consisted of convertible securities for which limited observable inputs were available at September 30, 2018 and December 31, 2017 . The securities were valued internally based on expected cash flows, including the expected final recovery, discounted at a yield that considered the lack of liquidity and the financial status of the issuer.

Basis of Presentation (Tables)

Basis of Presentation (Tables)	9 Months Ended
	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of other liabilities	Other liabilities consisted of the following: (In thousands) September 30, 2018 December 31, 2017 SPC dividends payable $ 54,591 $ 46,925 Unpaid dividends 16,622 267,292 All other 108,321 123,383 Total other liabilities $ 179,534 $ 437,600

Fair Value Measurement (Tables)

Fair Value Measurement (Tables)	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Schedule of fair value of assets	Fair values of assets measured at fair value on a recurring basis as of September 30, 2018 and December 31, 2017 are shown in the following tables. Where applicable, the tables also indicate the fair value hierarchy of the valuation techniques utilized to determine those fair values. For some assets, the inputs used to measure fair value may fall into different levels of the fair value hierarchy. When this is the case, the asset is categorized based on the level of the most significant input to the fair value measurement. Assessments of the significance of a particular input to the fair value measurement require judgment and consideration of factors specific to the assets being valued. September 30, 2018 Fair Value Measurements Using Total (In thousands) Level 1 Level 2 Level 3 Fair Value Assets: Fixed maturities, available for sale U.S. Treasury obligations $ — $ 125,072 $ — $ 125,072 U.S. Government-sponsored enterprise obligations — 35,882 — 35,882 State and municipal bonds — 310,188 — 310,188 Corporate debt, multiple observable inputs 2,367 1,229,540 — 1,231,907 Corporate debt, limited observable inputs — — 9,405 9,405 Residential mortgage-backed securities — 187,460 — 187,460 Agency commercial mortgage-backed securities — 13,544 — 13,544 Other commercial mortgage-backed securities — 31,411 — 31,411 Other asset-backed securities — 180,307 7,159 187,466 Fixed maturities, trading Corporate debt — 32,782 — 32,782 Equity investments Financial 77,159 — — 77,159 Utilities/Energy 59,460 — — 59,460 Consumer oriented 58,478 — — 58,478 Industrial 50,776 — — 50,776 Bond funds 211,513 — — 211,513 All other 45,966 — — 45,966 Short-term investments 171,061 33,512 — 204,573 Other investments — 32,862 6 32,868 Other assets — 2,852 — 2,852 Total assets categorized within the fair value hierarchy $ 676,780 $ 2,215,412 $ 16,570 2,908,762 Assets carried at NAV, which approximates fair value and which are not categorized within the fair value hierarchy, reported as a part of: Equity investments 20,416 Investment in unconsolidated subsidiaries 287,575 Total assets at fair value $ 3,216,753 December 31, 2017 Fair Value Measurements Using Total (In thousands) Level 1 Level 2 Level 3 Fair Value Assets: Fixed maturities, available for sale U.S. Treasury obligations $ — $ 133,627 $ — $ 133,627 U.S. Government-sponsored enterprise obligations — 20,956 — 20,956 State and municipal bonds — 632,243 — 632,243 Corporate debt, multiple observable inputs 2,371 1,151,084 — 1,153,455 Corporate debt, limited observable inputs — — 13,703 13,703 Residential mortgage-backed securities — 196,789 1,055 197,844 Agency commercial mortgage-backed securities — 10,742 — 10,742 Other commercial mortgage-backed securities — 15,961 — 15,961 Other asset-backed securities — 97,780 3,931 101,711 Equity investments Financial 76,051 — — 76,051 Utilities/Energy 54,388 — — 54,388 Consumer oriented 54,529 — — 54,529 Industrial 53,936 — — 53,936 Bond funds 156,563 — — 156,563 All other 75,142 — — 75,142 Short-term investments 404,204 27,922 — 432,126 Other investments 607 31,155 409 32,171 Other assets — 1,731 — 1,731 Total assets categorized within the fair value hierarchy $ 877,791 $ 2,319,990 $ 19,098 3,216,879 Assets carried at NAV, which approximates fair value and which are not categorized within the fair value hierarchy, reported as a part of: Investment in unconsolidated subsidiaries 210,759 Other investments 20,130 Total assets at fair value $ 3,447,768
Schedule of quantitative information regarding level 3 valuations	Quantitative Information Regarding Level 3 Valuations Fair Value at ($ in thousands) September 30, 2018 December 31, 2017 Valuation Technique Unobservable Input Range Assets: Corporate debt, limited observable inputs $9,405 $13,703 Market Comparable Comparability Adjustment 0% - 5% (2.5%) Discounted Cash Flows Comparability Adjustment 0% - 5% (2.5%) Residential mortgage-backed and other asset-backed securities $7,159 $4,986 Market Comparable Comparability Adjustment 0% - 5% (2.5%) Discounted Cash Flows Comparability Adjustment 0% - 5% (2.5%) Other investments $6 $409 Discounted Cash Flows Comparability Adjustment 0% - 10% (5%)
Schedule of fair value measurements - level 3 assets	The following tables (the Level 3 Tables) present summary information regarding changes in the fair value of assets measured at fair value using Level 3 inputs. September 30, 2018 Level 3 Fair Value Measurements – Assets (In thousands) Corporate Debt Asset-backed Securities Other investments Total Balance June 30, 2018 $ 8,380 $ 9,420 $ 5 $ 17,805 Total gains (losses) realized and unrealized: Included in earnings, as a part of: Net investment income (37 ) 1 — (36 ) Net realized investment gains (losses) — — 1 1 Included in other comprehensive income (12 ) 15 — 3 Purchases 2,000 — — 2,000 Sales (926 ) — — (926 ) Transfers in — — — — Transfers out — (2,277 ) — (2,277 ) Balance September 30, 2018 $ 9,405 $ 7,159 $ 6 $ 16,570 Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end $ — $ — $ — $ — September 30, 2018 Level 3 Fair Value Measurements – Assets (In thousands) Corporate Debt Asset-backed Securities Other investments Total Balance December 31, 2017 $ 13,703 $ 4,986 $ 409 $ 19,098 Total gains (losses) realized and unrealized: Included in earnings, as a part of: Net investment income (111 ) 2 — (109 ) Net realized investment gains (losses) (8 ) — (37 ) (45 ) Included in other comprehensive income (140 ) (126 ) — (266 ) Purchases 8,005 16,678 — 24,683 Sales (5,475 ) (185 ) (366 ) (6,026 ) Transfers in 2,627 — — 2,627 Transfers out (9,196 ) (14,196 ) — (23,392 ) Balance September 30, 2018 $ 9,405 $ 7,159 $ 6 $ 16,570 Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end $ — $ — $ — $ — September 30, 2017 Level 3 Fair Value Measurements – Assets (In thousands) Corporate Debt Asset-backed Securities Other investments Total Balance June 30, 2017 $ 17,849 $ 3,005 $ 5 $ 20,859 Total gains (losses) realized and unrealized: Included in earnings, as a part of: Net investment income (52 ) — — (52 ) Included in other comprehensive income (18 ) (45 ) — (63 ) Purchases 1 580 — 581 Sales (858 ) — — (858 ) Transfers in 989 — 423 1,412 Transfers out (2,948 ) — — (2,948 ) Balance September 30, 2017 $ 14,963 $ 3,540 $ 428 $ 18,931 Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end $ — $ — $ — $ — September 30, 2017 Level 3 Fair Value Measurements – Assets (In thousands) Corporate Debt Asset-backed Securities Other investments Total Balance December 31, 2016 $ 14,810 $ 3,007 $ 3 $ 17,820 Total gains (losses) realized and unrealized: Included in earnings, as a part of: Net investment income (125 ) — — (125 ) Net realized investment gains (losses) 13 — (124 ) (111 ) Included in other comprehensive income (296 ) (47 ) 140 (203 ) Purchases 11,890 580 — 12,470 Sales (4,418 ) — (912 ) (5,330 ) Transfers in 999 — 1,321 2,320 Transfers out (7,910 ) — — (7,910 ) Balance September 30, 2017 $ 14,963 $ 3,540 $ 428 $ 18,931 Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end $ — $ — $ — $ —
Schedule of investments in LLCs and limited partnerships	The amount of ProAssurance's unfunded commitments related to these investments as of September 30, 2018 and fair values of these investments as of September 30, 2018 and December 31, 2017 was as follows: Unfunded Fair Value (In thousands) September 30, September 30, December 31, Equity investments: Mortgage fund (1)* None $ 20,416 $ — Investment in unconsolidated subsidiaries: Private debt funds (2) $19,918 23,736 42,206 Long equity fund (3) None 6,899 7,847 Long/short equity funds (4) None 27,927 31,352 Non-public equity funds (5) $73,795 113,669 100,062 Multi-strategy fund of funds (6) None 9,447 9,100 Credit funds (7) $8,916 29,485 6,561 Long/short commodities fund (8) None 13,686 13,025 Strategy focused funds (9) $29,693 62,726 606 287,575 210,759 Other investments: Mortgage fund (1)* See above — 20,130 Total investments carried at NAV $ 307,991 $ 230,889 * In the first quarter of 2018, ProAssurance began presenting this investment previously reported as a part of other investments as a part of equity investments on the Condensed Consolidated Balance Sheet. Prior year amounts have not been reclassified. Below is additional information regarding each of the investments listed in the table above as of September 30, 2018 . (1) This investment fund is focused on the structured mortgage market. The fund will primarily invest in U.S. Agency mortgage-backed securities. Redemptions are allowed at the end of any calendar quarter with a prior notice requirement of 65 days and are paid within 45 days at the end of the redemption dealing day. (2) The investment is comprised of interests in three unrelated LP funds that are structured to provide interest distributions primarily through diversified portfolios of private debt instruments. One LP allows redemption by special consent; the other two do not permit redemption. Income and capital are to be periodically distributed at the discretion of the LP s over an anticipated time frame that spans from three to eight years. (3) The fund is a LP that holds long equities of public international companies. Redemptions are allowed at the end of any calendar month with a prior notice requirement of 15 days and are paid within 10 days of the end of the calendar month of the redemption request. (4) The investment is comprised of interests in multiple unrelated LP funds. The funds hold primarily long and short North American equities and target absolute returns using strategies designed to take advantage of market opportunities. The funds generally permit quarterly or semi-annual capital redemptions subject to notice requirements of 30 to 90 days . For some funds, redemptions above specified thresholds (lowest threshold is 90% ) may be only partially payable until after a fund audit is completed and are then payable within 30 days . (5) The investment is comprised of interests in multiple unrelated LP funds, each structured to provide capital appreciation through diversified investments in private equity, which can include investments in buyout, venture capital, debt including senior, second lien and mezzanine, distressed debt and other private equity-oriented LP s. Two of the LP s allow redemption by terms set forth in the LP agreements; the others do not permit redemption. Income and capital are to be periodically distributed at the discretion of the LP over time frames that are anticipated to span up to nine years. (6) This fund is a LLC structured to build and manage low volatility, multi-manager portfolios that have little or no correlation to the broader fixed income and equity security markets. Redemptions are not permitted but offers to repurchase units of the LLC may be extended periodically. (7) The investment is comprised of three unrelated LP funds. Two funds seek to obtain superior risk-adjusted absolute returns through a diversified portfolio of debt securities, including bonds, loans and other asset-backed instruments. The remaining fund seeks event driven opportunities across the corporate credit spectrum. Two funds are allowed redemptions at any quarter-end with a prior notice requirement of 90 days ; one fund permits redemption at any quarter-end with a prior notice requirement of 180 days . (8) This fund is a LLC invested across a broad range of commodities and focuses primarily on market neutral, relative value strategies, seeking to generate absolute returns with low correlation to broad commodity, equity and fixed income markets. Following an initial one-year lock-up period, redemptions are allowed with a prior notice requirement of 30 days and are payable within 30 days . (9) The investment is comprised of multiple unrelated LP s/ LLC s funds. One fund is a LLC focused on investing in North American consumer products companies, comprised of equity and equity-related securities, as well as debt instruments. Redemptions are not permitted. Another fund is a LP focused on North American energy infrastructure assets that allows redemption with consent of the General Partner. The remaining funds are real estate focused LP s, one of which allows for redemption with prior notice.
Schedule of financial instruments not measured at fair value	The following table provides the estimated fair value of our financial instruments that, in accordance with GAAP for the type of investment, are measured using a methodology other than fair value. All fair values provided primarily fall within the Level 3 fair value category. September 30, 2018 December 31, 2017 (In thousands) Carrying Fair Carrying Fair Financial assets: BOLI $ 63,638 $ 63,638 $ 62,113 $ 62,113 Other investments $ 2,930 $ 2,930 $ 58,546 $ 69,095 Other assets $ 38,405 $ 38,219 $ 34,020 $ 33,742 Financial liabilities: Senior notes due 2023* $ 250,000 $ 260,630 $ 250,000 $ 273,153 Revolving Credit Agreement* $ — $ — $ 123,000 $ 123,000 Mortgage loans* $ 39,413 $ 39,413 $ 40,460 $ 40,460 Other liabilities $ 23,186 $ 23,186 $ 21,154 $ 21,154 * Carrying value excludes debt issuance costs.

Investments (Tables)

Investments (Tables)	9 Months Ended
	Sep. 30, 2018
Investments, Debt and Equity Securities [Abstract]
Schedule of available-for-sale fixed maturities	Available-for-sale fixed maturities at September 30, 2018 and December 31, 2017 included the following: September 30, 2018 (In thousands) Amortized Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Fixed maturities, available for sale U.S. Treasury obligations $ 127,596 $ 164 $ 2,688 $ 125,072 U.S. Government-sponsored enterprise obligations 36,768 12 898 35,882 State and municipal bonds 308,712 3,900 2,424 310,188 Corporate debt 1,258,709 3,752 21,149 1,241,312 Residential mortgage-backed securities 192,859 793 6,192 187,460 Agency commercial mortgage-backed securities 13,893 — 349 13,544 Other commercial mortgage-backed securities 31,882 35 506 31,411 Other asset-backed securities 189,300 23 1,857 187,466 $ 2,159,719 $ 8,679 $ 36,063 $ 2,132,335 December 31, 2017 (In thousands) Amortized Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Fixed maturities, available for sale U.S. Treasury obligations $ 134,323 $ 485 $ 1,181 $ 133,627 U.S. Government-sponsored enterprise obligations 21,089 73 206 20,956 State and municipal bonds 618,414 14,248 419 632,243 Corporate debt 1,157,660 15,205 5,707 1,167,158 Residential mortgage-backed securities 196,741 2,438 1,335 197,844 Agency commercial mortgage-backed securities 10,827 23 108 10,742 Other commercial mortgage-backed securities 16,004 91 134 15,961 Other asset-backed securities 102,130 47 466 101,711 $ 2,257,188 $ 32,610 $ 9,556 $ 2,280,242
Schedule of available-for-sale securities by contractual maturity	The recorded cost basis and estimated fair value of available-for-sale fixed maturities at September 30, 2018 , by contractual maturity, are shown below. Actual maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. (In thousands) Amortized Due in one Due after Due after Due after Total Fair Fixed maturities, available for sale U.S. Treasury obligations $ 127,596 $ 27,456 $ 76,463 $ 18,501 $ 2,652 $ 125,072 U.S. Government-sponsored enterprise obligations 36,768 3,276 12,973 19,502 131 35,882 State and municipal bonds 308,712 26,232 108,583 144,847 30,526 310,188 Corporate debt 1,258,709 144,784 714,013 352,691 29,824 1,241,312 Residential mortgage-backed securities 192,859 187,460 Agency commercial mortgage-backed securities 13,893 13,544 Other commercial mortgage-backed securities 31,882 31,411 Other asset-backed securities 189,300 187,466 $ 2,159,719 $ 2,132,335
Schedule of investments held in an unrealized loss position	The following tables provide summarized information with respect to investments held in an unrealized loss position at September 30, 2018 and December 31, 2017 , including the length of time the investment had been held in a continuous unrealized loss position. September 30, 2018 Total Less than 12 months 12 months or longer Fair Unrealized Fair Unrealized Fair Unrealized (In thousands) Value Loss Value Loss Value Loss Fixed maturities, available for sale U.S. Treasury obligations $ 118,159 $ 2,688 $ 62,352 $ 1,020 $ 55,807 $ 1,668 U.S. Government-sponsored enterprise obligations 34,713 898 22,082 364 12,631 534 State and municipal bonds 134,549 2,424 125,853 2,135 8,696 289 Corporate debt 967,853 21,149 746,194 13,342 221,659 7,807 Residential mortgage-backed securities 167,145 6,192 92,516 2,348 74,629 3,844 Agency commercial mortgage-backed securities 13,544 349 9,416 105 4,128 244 Other commercial mortgage-backed securities 29,076 506 24,184 322 4,892 184 Other asset-backed securities 167,353 1,857 131,437 1,308 35,916 549 $ 1,632,392 $ 36,063 $ 1,214,034 $ 20,944 $ 418,358 $ 15,119 December 31, 2017 Total Less than 12 months 12 months or longer Fair Unrealized Fair Unrealized Fair Unrealized (In thousands) Value Loss Value Loss Value Loss Fixed maturities, available for sale U.S. Treasury obligations $ 110,788 $ 1,181 $ 67,135 $ 554 $ 43,653 $ 627 U.S. Government-sponsored enterprise obligations 17,032 206 10,182 64 6,850 142 State and municipal bonds 23,122 419 15,168 102 7,954 317 Corporate debt 487,578 5,707 365,541 2,730 122,037 2,977 Residential mortgage-backed securities 109,659 1,335 64,121 402 45,538 933 Agency commercial mortgage-backed securities 4,423 108 2,458 34 1,965 74 Other commercial mortgage-backed securities 12,878 134 7,939 82 4,939 52 Other asset-backed securities 85,358 466 70,924 346 14,434 120 $ 850,838 $ 9,556 $ 603,468 $ 4,314 $ 247,370 $ 5,242
Schedule of other information regarding available-for-sale securities	Other information regarding sales and purchases of fixed maturity available-for-sale securities is as follows: Three Months Ended September 30 Nine Months Ended September 30 (In millions) 2018 2017 2018 2017 Proceeds from sales (exclusive of maturities and paydowns) $ 61.3 $ 74.1 $ 556.3 $ 309.6 Purchases $ 164.6 $ 90.6 $ 717.1 $ 449.7
Schedule of net investment income	Net investment income by investment category was as follows: Three Months Ended Nine Months Ended (In thousands) 2018 2017 2018 2017 Fixed maturities $ 17,228 $ 18,924 $ 51,814 $ 57,885 Equities 5,687 4,495 15,553 12,437 Short-term investments, including Other 1,330 1,147 3,968 2,926 BOLI 621 620 1,525 1,517 Investment fees and expenses (1,600 ) (1,457 ) (5,183 ) (5,173 ) Net investment income $ 23,266 $ 23,729 $ 67,677 $ 69,592
Schedule of investment in unconsolidated subsidiaries	ProAssurance's investment in unconsolidated subsidiaries were as follows: September 30, 2018 Carrying Value (In thousands) Percentage September 30, December 31, Qualified affordable housing project tax credit partnerships See below $ 70,217 $ 84,607 Other tax credit partnerships See below 4,414 6,118 All other investments, primarily investment fund LPs/LLCs See below 316,107 239,866 $ 390,738 $ 330,591
Schedule of losses and tax credits related to tax credit partnership investments	Losses recorded and tax credits recognized related to ProAssurance's tax credit partnership investments were as follows: Three Months Ended Nine Months Ended (In thousands) 2018 2017 2018 2017 Qualified affordable housing project tax credit partnerships Losses recorded $ 4,661 $ 3,442 $ 14,373 $ 10,713 Tax credits recognized $ 4,618 $ 4,608 $ 13,855 $ 13,833 Historic tax credit partnerships Losses recorded $ 1,394 $ 621 $ 4,776 $ 3,388 Tax credits recognized $ 570 $ 1,352 $ 1,925 $ 3,976
Schedule of net realized investment gains (losses)	Realized investment gains and losses are recognized on the first-in, first-out basis. The following table provides detailed information regarding net realized investment gains (losses): Three Months Ended Nine Months Ended (In thousands) 2018 2017 2018 2017 Total OTTI losses: Corporate debt $ (86 ) $ — $ (490 ) $ (419 ) Portion of OTTI losses recognized in other comprehensive income before taxes: Corporate debt — — — 248 Net impairment losses recognized in earnings (86 ) — (490 ) (171 ) Gross realized gains, available-for-sale fixed maturities 690 1,724 5,592 4,323 Gross realized (losses), available-for-sale fixed maturities (1,400 ) (262 ) (5,172 ) (1,730 ) Net realized gains (losses), short-term investments — (1 ) — (1 ) Net realized gains (losses), trading fixed maturities (28 ) — (100 ) — Net realized gains (losses), equity investments 4,689 3,603 17,395 10,958 Net realized gains (losses), other investments 561 478 1,652 2,197 Change in unrealized holding gains (losses), trading fixed maturities (42 ) — (261 ) — Change in unrealized holding gains (losses), equity investments 7,996 2,182 (15,104 ) 2,606 Change in unrealized holding gains (losses), convertible securities, carried at fair value (260 ) 23 (1,126 ) 621 Other 253 2 265 7 Net realized investment gains (losses) $ 12,373 $ 7,749 $ 2,651 $ 18,810
Schedule of OTTI recorded in OCI	The following table presents a roll forward of cumulative credit losses recorded in earnings related to impaired debt securities for which a portion of the OTTI was recorded in OCI . Three Months Ended Nine Months Ended (In thousands) 2018 2017 2018 2017 Balance beginning of period $ 1,313 $ 1,313 $ 1,313 $ 1,158 Additional credit losses recognized during the period, related to securities for which: No OTTI has been previously recognized — — — 171 Reductions due to: Securities sold during the period (realized) (1,220 ) — (1,220 ) (16 ) Balance September 30 $ 93 $ 1,313 $ 93 $ 1,313

Reserve for Losses and Loss A_2

Reserve for Losses and Loss Adjustment Expenses (Tables)	9 Months Ended
	Sep. 30, 2018
Insurance [Abstract]
Summary of reserve for losses and loss adjustment expenses	Activity in the reserve for losses and loss adjustment expenses is summarized as follows: (In thousands) Nine Months Ended September 30, 2018 Nine Months Ended September 30, 2017 Year Ended December 31, 2017 Balance, beginning of year $ 2,048,381 $ 1,993,428 $ 1,993,428 Less reinsurance recoverables on unpaid losses and loss adjustment expenses 335,585 273,475 273,475 Net balance, beginning of year 1,712,796 1,719,953 1,719,953 Net losses: Current year* 506,269 454,121 603,518 Favorable development of reserves established in prior years, net (67,149 ) (90,063 ) (134,360 ) Total 439,120 364,058 469,158 Paid related to: Current year (69,881 ) (63,667 ) (106,633 ) Prior years (314,763 ) (293,522 ) (369,682 ) Total paid (384,644 ) (357,189 ) (476,315 ) Net balance, end of period 1,767,272 1,726,822 1,712,796 Plus reinsurance recoverables on unpaid losses and loss adjustment expenses 332,555 313,876 335,585 Balance, end of period $ 2,099,827 $ 2,040,698 $ 2,048,381 * Current year net losses during the 2018 nine-month period included incurred losses of $25.4 million related to a loss portfolio transfer entered into during the second quarter of 2018 (see Note 4).

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Schedule of outstanding debt	ProAssurance’s outstanding debt consisted of the following: (In thousands) September 30, December 31, Senior Notes due 2023, unsecured, interest at 5.3% annually $ 250,000 $ 250,000 Revolving Credit Agreement, outstanding borrowings were fully secured and carried at a weighted average interest rate of 1.91%. Outstanding borrowings are not permitted to exceed $250 million aggregately; Revolving Credit Agreement expires in 2020. The interest rate on borrowings is set at the time the respective borrowing is initiated or renewed. — 123,000 Mortgage Loans, outstanding borrowings are secured by first priority liens on two office buildings, and bear an interest rate of three-month LIBOR plus 1.325% (3.66% and 2.86%, respectively) determined on a quarterly basis. 39,413 40,460 Total principal 289,413 413,460 Less debt issuance costs 1,399 1,649 Debt less debt issuance costs $ 288,014 $ 411,811

Derivatives (Tables)

Derivatives (Tables)	9 Months Ended
	Sep. 30, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of interest rate caps	The following table provides a summary of the volume and fair value position of the interest rate cap as well as the reporting location in the Condensed Consolidated Balance Sheets as of September 30, 2018 and December 31, 2017 . ($ in thousands) September 30, 2018 December 31, 2017 Derivatives Not Designated as Hedging Instruments Location in the Condensed Consolidated Balance Sheets Number of Instruments Notional Amount (1) Estimated Fair Value (2) Number of Instruments Notional Amount (1) Estimated Fair Value (2) Interest Rate Cap Other assets 1 $ 35,000 $ 2,852 1 $ 35,000 $ 1,731 (1) Volume is represented by the derivative instrument's notional amount. (2) Additional information regarding the fair value of the Company's interest rate cap is provided in Note 2. The following table presents the pre-tax impact of the change in the fair value of the interest rate cap and the reporting location in the Condensed Consolidated Statements of Income and Comprehensive Income for the three and nine months ended September 30, 2018 and 2017 . Gains (Losses) Recognized in Income on Derivatives (In thousands) Three Months Ended September 30 Nine Months Ended September 30 Derivatives Not Designated as Hedging Instruments Location in the Condensed Consolidated Statements of Income and Comprehensive Income 2018 2017 2018 2017 Interest Rate Cap Interest expense $ 264 $ — $ 1,121 $ —

Shareholders' Equity (Tables)

Shareholders' Equity (Tables)	9 Months Ended
	Sep. 30, 2018
Equity [Abstract]
Schedule of share-based compensation expense and related tax benefits	Share-based compensation expense and related tax benefits were as follows: Three Months Ended September 30 Nine Months Ended September 30 (In thousands) 2018 2017 2018 2017 Share-based compensation expense $ 1,628 $ 1,018 $ 4,145 $ 7,110 Related tax benefits $ 342 $ 356 $ 870 $ 2,489
Schedule of reclassification adjustments related to available-for-sale securities	Amounts reclassified from AOCI to net income and the amounts of deferred tax expense (benefit) included in OCI were as follows: Three Months Ended September 30 Nine Months Ended September 30 (In thousands) 2018 2017 2018 2017 Reclassifications from AOCI to net income: Realized investment gains (losses) $ (175 ) $ 1,462 $ 551 $ 2,425 Non-credit impairment losses reclassified to earnings, due to sale of securities or reclassification as a credit loss (621 ) — (621 ) (3 ) Total gains (losses) reclassified, before tax effect (796 ) 1,462 (70 ) 2,422 Tax effect* 167 (512 ) 15 (848 ) Net reclassification adjustments $ (629 ) $ 950 $ (55 ) $ 1,574 Deferred tax expense (benefit) included in OCI $ (1,197 ) $ (373 ) $ (10,442 ) $ 4,091 * Tax effects were computed using a 21% and 35% rate for the three and nine months ended September 30, 2018 and 2017, respectively.

Earnings Per Share (Tables)

Earnings Per Share (Tables)	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Schedule of earnings per share, basic and diluted	The following table provides the weighted average number of common shares outstanding used in the calculation of the Company's basic and diluted earnings per share: (In thousands, except per share data) Three Months Ended September 30 Nine Months Ended September 30 2018 2017 2018 2017 Weighted average number of common shares outstanding, basic 53,620 53,413 53,585 53,377 Dilutive effect of securities: Restricted Share Units 83 87 78 81 Performance Share Units 48 88 52 105 Purchase Match Units 22 26 20 23 Weighted average number of common shares outstanding, diluted 53,773 53,614 53,735 53,586 Effect of dilutive shares on earnings per share $ — $ — $ — $ —

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2018
Segment Reporting [Abstract]
Schedule of segment reporting information, by segment	Financial results by segment were as follows: Three Months Ended September 30, 2018 (In thousands) Specialty P&C Workers' Compensation Insurance Segregated Portfolio Cell Reinsurance Lloyd's Syndicates Corporate Inter-segment Eliminations Consolidated Net premiums earned $ 120,789 $ 47,296 $ 18,963 $ 19,022 $ — $ — $ 206,070 Net investment income — — 371 783 22,112 — 23,266 Equity in earnings (loss) of unconsolidated subsidiaries — — — — 5,228 — 5,228 Net realized gains (losses) — — 1,397 (98 ) 11,074 — 12,373 Other income (expense) (1) 1,426 376 86 352 699 (551 ) 2,388 Net losses and loss adjustment expenses (98,363 ) (30,650 ) (8,560 ) (10,032 ) — — (147,605 ) Underwriting, policy acquisition and operating expenses (1) (27,931 ) (15,410 ) (5,516 ) (8,439 ) (5,053 ) 505 (61,844 ) Segregated portfolio cells dividend (expense) income — — (5,255 ) — — — (5,255 ) Interest expense — — — — (3,645 ) 46 (3,599 ) Income tax benefit (expense) — — — 361 (155 ) — 206 Segment operating results $ (4,079 ) $ 1,612 $ 1,486 $ 1,949 $ 30,260 $ — $ 31,228 Significant non-cash items: Depreciation and amortization, net of accretion $ 1,715 $ 959 $ 83 $ (2 ) $ 2,751 $ — $ 5,506 Nine Months Ended September 30, 2018 (In thousands) Specialty P&C Workers' Compensation Insurance Segregated Portfolio Cell Reinsurance Lloyd's Syndicates Corporate Inter-segment Eliminations Consolidated Net premiums earned $ 378,355 $ 135,230 $ 54,247 $ 48,987 $ — $ — $ 616,819 Net investment income — — 1,100 2,370 64,207 — 67,677 Equity in earnings (loss) of unconsolidated subsidiaries — — — — 12,247 — 12,247 Net realized gains (losses) — — 467 (404 ) 2,588 — 2,651 Other income (expense) (1) 3,945 1,828 176 247 2,737 (1,778 ) 7,155 Net losses and loss adjustment expenses (292,742 ) (87,794 ) (27,561 ) (31,023 ) — — (439,120 ) Underwriting, policy acquisition and operating expenses (1) (83,833 ) (41,545 ) (16,070 ) (23,745 ) (15,351 ) 1,732 (178,812 ) Segregated portfolio cells dividend (expense) income — — (9,787 ) — — — (9,787 ) Interest expense — — — — (11,308 ) 46 (11,262 ) Income tax benefit (expense) — — — 355 3,584 — 3,939 Segment operating results $ 5,725 $ 7,719 $ 2,572 $ (3,213 ) $ 58,704 $ — $ 71,507 Significant non-cash items: Depreciation and amortization, net of accretion $ 5,343 $ 2,873 $ 393 $ (5 ) $ 7,940 $ — $ 16,544 Three Months Ended September 30, 2017 (In thousands) Specialty P&C Workers' Compensation Insurance Segregated Portfolio Cell Reinsurance Lloyd's Syndicates Corporate Inter-segment Eliminations Consolidated Net premiums earned $ 117,288 $ 41,540 $ 17,157 $ 16,318 $ — $ — $ 192,303 Net investment income — — 290 412 23,027 — 23,729 Equity in earnings (loss) of unconsolidated subsidiaries — — — — 4,164 — 4,164 Net realized gains (losses) — — 944 31 6,774 — 7,749 Other income (expense) (1) 1,276 535 33 (1,881 ) 1,023 (476 ) 510 Net losses and loss adjustment expenses (72,944 ) (27,065 ) (8,903 ) (20,444 ) — — (129,356 ) Underwriting, policy acquisition and operating expenses (1) (26,816 ) (13,912 ) (5,147 ) (6,723 ) (4,989 ) 476 (57,111 ) Segregated portfolio cells dividend (expense) income — — (2,891 ) — — — (2,891 ) Interest expense — — — — (4,124 ) — (4,124 ) Income tax benefit (expense) — — — (61 ) (5,963 ) — (6,024 ) Segment operating results $ 18,804 $ 1,098 $ 1,483 $ (12,348 ) $ 19,912 $ — $ 28,949 Significant non-cash items: Depreciation and amortization, net of accretion $ 1,933 $ 848 $ 176 $ (6 ) $ 4,124 $ — $ 7,075 Nine Months Ended September 30, 2017 (In thousands) Specialty P&C Workers' Compensation Insurance Segregated Portfolio Cell Reinsurance Lloyd's Syndicates Corporate Inter-segment Eliminations Consolidated Net premiums earned $ 337,287 $ 122,247 $ 50,651 $ 45,374 $ — $ — $ 555,559 Net investment income — — 742 1,194 67,656 — 69,592 Equity in earnings (loss) of unconsolidated subsidiaries — — — — 8,489 — 8,489 Net realized gains (losses) — — 2,715 105 15,990 — 18,810 Other income (expense) (1) 3,943 1,716 83 (1,641 ) 1,974 (1,494 ) 4,581 Net losses and loss adjustment expenses (217,512 ) (79,520 ) (26,308 ) (40,718 ) — — (364,058 ) Underwriting, policy acquisition and operating expenses (1) (78,601 ) (38,912 ) (15,239 ) (19,786 ) (21,062 ) 1,494 (172,106 ) Segregated portfolio cells dividend (expense) income (2) (5,181 ) — (8,895 ) — — — (14,076 ) Interest expense — — — — (12,402 ) — (12,402 ) Income tax benefit (expense) (2) — — — 495 (4,962 ) — (4,467 ) Segment operating results $ 39,936 $ 5,531 $ 3,749 $ (14,977 ) $ 55,683 $ — $ 89,922 Significant non-cash items: Depreciation and amortization, net of accretion $ 5,350 $ 2,516 $ 500 $ (14 ) $ 12,672 $ — $ 21,024 (1) As a result of the third quarter 2018 segment reorganization, certain fees for services provided to the SPCs at Eastern Re and Inova Re are recorded as expenses within the Segregated Portfolio Cell Reinsurance segment and as other income within the Workers' Compensation Insurance segment. These fees are eliminated between segments in consolidation. These services primarily include SPC rental fees and were previously eliminated within the Company's Workers' Compensation segment. (2) During the second quarter of 2017, ProAssurance recognized a $5.2 million pre-tax expense related to previously unrecognized SPC dividend expense for the cumulative earnings of unrelated parties that have owned segregated portfolio cells at various periods since 2003 in a Bermuda captive insurance operation managed by the Company's HCPL line of business within the Specialty P&C segment. The expense recorded in the second quarter of 2017 related to periods prior to the then current period and was unrelated to the captive operations of the Company's Eastern Re subsidiary. The $1.8 million tax impact of the expense recognized in the second quarter of 2017 was included in the Corporate segment's income tax benefit (expense).
Schedule of gross premiums by product	The following table provides detailed information regarding ProAssurance's gross premiums earned by product as well as a reconciliation to net premiums earned. All gross premiums earned are from external customers except as noted. ProAssurance's insured risks are primarily within the U.S. Three Months Ended September 30 Nine Months Ended September 30 (In thousands) 2018 2017 2018 2017 Specialty P&C Segment Gross premiums earned: Healthcare professional liability $ 126,012 $ 125,377 $ 390,904 $ 358,209 Legal professional liability 6,606 6,483 19,486 19,217 Medical technology liability 9,080 8,459 26,372 25,160 Other 113 108 346 311 Ceded premiums earned (21,022 ) (23,139 ) (58,753 ) (65,610 ) Segment net premiums earned 120,789 117,288 378,355 337,287 Workers' Compensation Insurance Segment Gross premiums earned: Traditional business 50,271 43,734 145,334 128,203 Alternative market business 21,564 20,200 61,593 59,855 Ceded premiums earned (24,539 ) (22,394 ) (71,697 ) (65,811 ) Segment net premiums earned 47,296 41,540 135,230 122,247 Segregated Portfolio Cell Reinsurance Segment Gross premiums earned: Workers' compensation (1) 20,251 18,296 57,287 54,016 Healthcare professional liability (2) 1,225 1,044 3,782 3,106 Ceded premiums earned (2,513 ) (2,183 ) (6,822 ) (6,471 ) Segment net premiums earned 18,963 17,157 54,247 50,651 Lloyd's Syndicates Segment Gross premiums earned: Property and casualty (3) 23,050 18,790 60,289 52,935 Ceded premiums earned (4,028 ) (2,472 ) (11,302 ) (7,561 ) Segment net premiums earned 19,022 16,318 48,987 45,374 Consolidated net premiums earned $ 206,070 $ 192,303 $ 616,819 $ 555,559 (1) Premium for all periods is assumed from the Workers' Compensation Insurance segment. (2) Premium for all periods is assumed from the Specialty P&C segment. (3) Includes premium assumed from the Specialty P&C segment of $1.2 million and $4.5 million for the three and nine months ended September 30, 2018 , respectively, and $2.9 million and $9.5 million for the same respective periods of 2017 .

Basis of Presentation (Narrativ

Basis of Presentation (Narrative) (Details) $ in Thousands		3 Months Ended	9 Months Ended
		Sep. 30, 2018USD ($)	Sep. 30, 2018USD ($)segment	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of reportable segments | segment			5
Distributed earnings from unconsolidated subsidiaries			$ 23,906	$ 20,150
Changes in fair value of investments previously reported as cost method investments		$ 5,200	11,100
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification from AOCI to retained earnings for stranded tax effects			(3,400)
Accumulated Other Comprehensive Income (Loss)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification from AOCI to retained earnings for stranded tax effects			$ 3,400
Accounting Standards Update 2016-15
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Distributions from unconsolidated subsidiaries, investing activities				20,200
Distributed earnings from unconsolidated subsidiaries				$ 20,200
Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative-effect adjustment adoption of ASU	[1]				$ 8,334
Accounting Standards Update 2016-01 | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative-effect adjustment adoption of ASU	[1]				$ 8,334
[1]	See Note 1 for discussion of accounting guidance adopted during the period.

Basis of Presentation (Other Li

Basis of Presentation (Other Liabilities) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
SPC dividends payable	$ 54,591	$ 46,925
Unpaid dividends	16,622	267,292	$ 16,558
All other	108,321	123,383
Total other liabilities	$ 179,534	$ 437,600

Fair Value Measurement (Assets

Fair Value Measurement (Assets Measured at Fair Value) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Assets:
Fixed maturities, available for sale	$ 2,132,335	$ 2,280,242
Equity investments	523,768	470,609
Assets carried at NAV, which approximates fair value and which are not categorized within the fair value hierarchy	307,991	230,889
Investment in unconsolidated subsidiaries
Assets:
Assets carried at NAV, which approximates fair value and which are not categorized within the fair value hierarchy	287,575	210,759
Level 3 | Corporate debt, limited observable inputs
Assets:
Total assets categorized within the fair value hierarchy	9,405	13,703
Level 3 | Other investments
Assets:
Total assets categorized within the fair value hierarchy	6	409
Recurring
Assets:
Other assets	2,852	1,731
Total assets categorized within the fair value hierarchy	2,908,762	3,216,879
Total assets at fair value	3,216,753	3,447,768
Recurring | U.S. Treasury obligations
Assets:
Fixed maturities, available for sale	125,072	133,627
Recurring | U.S. Government-sponsored enterprise obligations
Assets:
Fixed maturities, available for sale	35,882	20,956
Recurring | State and municipal bonds
Assets:
Fixed maturities, available for sale	310,188	632,243
Recurring | Corporate debt, multiple observable inputs
Assets:
Fixed maturities, available for sale	1,231,907	1,153,455
Recurring | Corporate debt, limited observable inputs
Assets:
Fixed maturities, available for sale	9,405	13,703
Recurring | Residential mortgage-backed securities
Assets:
Fixed maturities, available for sale	187,460	197,844
Recurring | Agency commercial mortgage-backed securities
Assets:
Fixed maturities, available for sale	13,544	10,742
Recurring | Other commercial mortgage-backed securities
Assets:
Fixed maturities, available for sale	31,411	15,961
Recurring | Other asset-backed securities
Assets:
Fixed maturities, available for sale	187,466	101,711
Recurring | Corporate Debt
Assets:
Fixed maturities, trading	32,782
Recurring | Financial
Assets:
Equity investments	77,159	76,051
Recurring | Utilities/Energy
Assets:
Equity investments	59,460	54,388
Recurring | Consumer oriented
Assets:
Equity investments	58,478	54,529
Recurring | Industrial
Assets:
Equity investments	50,776	53,936
Recurring | Bond funds
Assets:
Equity investments	211,513	156,563
Recurring | All other
Assets:
Equity investments	45,966	75,142
Recurring | Short-term investments
Assets:
Short-term and other investments	204,573	432,126
Recurring | Other investments
Assets:
Short-term and other investments	32,868	32,171
Assets carried at NAV, which approximates fair value and which are not categorized within the fair value hierarchy		20,130
Recurring | Equities
Assets:
Assets carried at NAV, which approximates fair value and which are not categorized within the fair value hierarchy	20,416
Recurring | Investment in unconsolidated subsidiaries
Assets:
Assets carried at NAV, which approximates fair value and which are not categorized within the fair value hierarchy	287,575	210,759
Recurring | Level 1
Assets:
Other assets	0	0
Total assets categorized within the fair value hierarchy	676,780	877,791
Recurring | Level 1 | U.S. Treasury obligations
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 1 | U.S. Government-sponsored enterprise obligations
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 1 | State and municipal bonds
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 1 | Corporate debt, multiple observable inputs
Assets:
Fixed maturities, available for sale	2,367	2,371
Recurring | Level 1 | Corporate debt, limited observable inputs
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 1 | Residential mortgage-backed securities
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 1 | Agency commercial mortgage-backed securities
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 1 | Other commercial mortgage-backed securities
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 1 | Other asset-backed securities
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 1 | Corporate Debt
Assets:
Fixed maturities, trading	0
Recurring | Level 1 | Financial
Assets:
Equity investments	77,159	76,051
Recurring | Level 1 | Utilities/Energy
Assets:
Equity investments	59,460	54,388
Recurring | Level 1 | Consumer oriented
Assets:
Equity investments	58,478	54,529
Recurring | Level 1 | Industrial
Assets:
Equity investments	50,776	53,936
Recurring | Level 1 | Bond funds
Assets:
Equity investments	211,513	156,563
Recurring | Level 1 | All other
Assets:
Equity investments	45,966	75,142
Recurring | Level 1 | Short-term investments
Assets:
Short-term and other investments	171,061	404,204
Recurring | Level 1 | Other investments
Assets:
Short-term and other investments	0	607
Recurring | Level 2
Assets:
Other assets	2,852	1,731
Total assets categorized within the fair value hierarchy	2,215,412	2,319,990
Recurring | Level 2 | U.S. Treasury obligations
Assets:
Fixed maturities, available for sale	125,072	133,627
Recurring | Level 2 | U.S. Government-sponsored enterprise obligations
Assets:
Fixed maturities, available for sale	35,882	20,956
Recurring | Level 2 | State and municipal bonds
Assets:
Fixed maturities, available for sale	310,188	632,243
Recurring | Level 2 | Corporate debt, multiple observable inputs
Assets:
Fixed maturities, available for sale	1,229,540	1,151,084
Recurring | Level 2 | Corporate debt, limited observable inputs
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 2 | Residential mortgage-backed securities
Assets:
Fixed maturities, available for sale	187,460	196,789
Recurring | Level 2 | Agency commercial mortgage-backed securities
Assets:
Fixed maturities, available for sale	13,544	10,742
Recurring | Level 2 | Other commercial mortgage-backed securities
Assets:
Fixed maturities, available for sale	31,411	15,961
Recurring | Level 2 | Other asset-backed securities
Assets:
Fixed maturities, available for sale	180,307	97,780
Recurring | Level 2 | Corporate Debt
Assets:
Fixed maturities, trading	32,782
Recurring | Level 2 | Financial
Assets:
Equity investments	0	0
Recurring | Level 2 | Utilities/Energy
Assets:
Equity investments	0	0
Recurring | Level 2 | Consumer oriented
Assets:
Equity investments	0	0
Recurring | Level 2 | Industrial
Assets:
Equity investments	0	0
Recurring | Level 2 | Bond funds
Assets:
Equity investments	0	0
Recurring | Level 2 | All other
Assets:
Equity investments	0	0
Recurring | Level 2 | Short-term investments
Assets:
Short-term and other investments	33,512	27,922
Recurring | Level 2 | Other investments
Assets:
Short-term and other investments	32,862	31,155
Recurring | Level 3
Assets:
Other assets	0	0
Total assets categorized within the fair value hierarchy	16,570	19,098
Recurring | Level 3 | U.S. Treasury obligations
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 3 | U.S. Government-sponsored enterprise obligations
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 3 | State and municipal bonds
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 3 | Corporate debt, multiple observable inputs
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 3 | Corporate debt, limited observable inputs
Assets:
Fixed maturities, available for sale	9,405	13,703
Recurring | Level 3 | Residential mortgage-backed securities
Assets:
Fixed maturities, available for sale	0	1,055
Recurring | Level 3 | Agency commercial mortgage-backed securities
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 3 | Other commercial mortgage-backed securities
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 3 | Other asset-backed securities
Assets:
Fixed maturities, available for sale	7,159	3,931
Recurring | Level 3 | Corporate Debt
Assets:
Fixed maturities, trading	0
Recurring | Level 3 | Financial
Assets:
Equity investments	0	0
Recurring | Level 3 | Utilities/Energy
Assets:
Equity investments	0	0
Recurring | Level 3 | Consumer oriented
Assets:
Equity investments	0	0
Recurring | Level 3 | Industrial
Assets:
Equity investments	0	0
Recurring | Level 3 | Bond funds
Assets:
Equity investments	0	0
Recurring | Level 3 | All other
Assets:
Equity investments	0	0
Recurring | Level 3 | Short-term investments
Assets:
Short-term and other investments	0	0
Recurring | Level 3 | Other investments
Assets:
Short-term and other investments	$ 6	$ 409

Fair Value Measurement (Narrati

Fair Value Measurement (Narrative) (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018USD ($)Agreement	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)Agreement	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)
Credit Derivatives [Line Items]
Net impairment losses recognized in earnings	$ 86,000	$ 0	$ 490,000	$ 171,000
Fair value of funded deferred compensation assets	$ 23,200,000		$ 23,200,000		$ 20,200,000
Separate line of credit agreements (in agreements) | Agreement	2		2
Early Stage Business Development | Investment in unconsolidated subsidiaries
Credit Derivatives [Line Items]
Net impairment losses recognized in earnings					8,500,000
Fair Value, Measurements, Nonrecurring
Credit Derivatives [Line Items]
Fair value, net asset (liability)	$ 0		$ 0		$ 1,200,000
Corporate debt, limited observable inputs | NRSRO | NRSRO, Rating BBBplus
Credit Derivatives [Line Items]
Credit rating			79.00%		84.00%
Residential mortgage-backed and other asset-backed securities | NRSRO | NRSRO, Rating AAA
Credit Derivatives [Line Items]
Credit rating			60.00%		21.00%

Fair Value Measurement (Quantit

Fair Value Measurement (Quantitative Information Regarding Level 3 Valuations) (Details) - Level 3 - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Corporate debt, limited observable inputs
Assets:
Assets measured at fair value	$ 9,405	$ 13,703
Corporate debt, limited observable inputs | Measurement input, comparability adjustment | Market Comparable Securities | Minimum
Assets:
Debt Securities, Available-for-sale, Measurement Input	0
Corporate debt, limited observable inputs | Measurement input, comparability adjustment | Market Comparable Securities | Maximum
Assets:
Debt Securities, Available-for-sale, Measurement Input	0.05
Corporate debt, limited observable inputs | Measurement input, comparability adjustment | Market Comparable Securities | Weighted average
Assets:
Debt Securities, Available-for-sale, Measurement Input	0.025
Corporate debt, limited observable inputs | Measurement input, comparability adjustment | Discounted Cash Flows | Minimum
Assets:
Debt Securities, Available-for-sale, Measurement Input	0
Corporate debt, limited observable inputs | Measurement input, comparability adjustment | Discounted Cash Flows | Maximum
Assets:
Debt Securities, Available-for-sale, Measurement Input	0.05
Corporate debt, limited observable inputs | Measurement input, comparability adjustment | Discounted Cash Flows | Weighted average
Assets:
Debt Securities, Available-for-sale, Measurement Input	0.025
Residential mortgage-backed and other asset-backed securities
Assets:
Assets measured at fair value	$ 7,159	4,986
Residential mortgage-backed and other asset-backed securities | Measurement input, comparability adjustment | Market Comparable Securities | Minimum
Assets:
Debt Securities, Available-for-sale, Measurement Input	0
Residential mortgage-backed and other asset-backed securities | Measurement input, comparability adjustment | Market Comparable Securities | Maximum
Assets:
Debt Securities, Available-for-sale, Measurement Input	0.05
Residential mortgage-backed and other asset-backed securities | Measurement input, comparability adjustment | Market Comparable Securities | Weighted average
Assets:
Debt Securities, Available-for-sale, Measurement Input	0.025
Residential mortgage-backed and other asset-backed securities | Measurement input, comparability adjustment | Discounted Cash Flows | Minimum
Assets:
Debt Securities, Available-for-sale, Measurement Input	0
Residential mortgage-backed and other asset-backed securities | Measurement input, comparability adjustment | Discounted Cash Flows | Maximum
Assets:
Debt Securities, Available-for-sale, Measurement Input	0.05
Residential mortgage-backed and other asset-backed securities | Measurement input, comparability adjustment | Discounted Cash Flows | Weighted average
Assets:
Debt Securities, Available-for-sale, Measurement Input	0.025
Other investments
Assets:
Assets measured at fair value	$ 6	$ 409
Other investments | Measurement input, comparability adjustment | Discounted Cash Flows | Minimum
Assets:
Derivative asset, measurement input	0.00%
Other investments | Measurement input, comparability adjustment | Discounted Cash Flows | Maximum
Assets:
Derivative asset, measurement input	10.00%
Other investments | Measurement input, comparability adjustment | Discounted Cash Flows | Weighted average
Assets:
Derivative asset, measurement input	5.00%

Fair Value Measurement (Fair Va

Fair Value Measurement (Fair Value Measurements - Level 3 Assets) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation:
Beginning balance	$ 17,805	$ 20,859	$ 19,098	$ 17,820
Included in earnings, as a part of:
Included in other comprehensive income	3	(63)	(266)	(203)
Purchases	2,000	581	24,683	12,470
Sales	(926)	(858)	(6,026)	(5,330)
Transfers in	0	1,412	2,627	2,320
Transfers out	(2,277)	(2,948)	(23,392)	(7,910)
Ending balance	16,570	18,931	16,570	18,931
Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end	0	0	0	0
Net investment income
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	(36)	(52)	(109)	(125)
Net realized investment gains (losses)
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	1		(45)	(111)
Corporate Debt
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation:
Beginning balance	8,380	17,849	13,703	14,810
Included in earnings, as a part of:
Included in other comprehensive income	(12)	(18)	(140)	(296)
Purchases	2,000	1	8,005	11,890
Sales	(926)	(858)	(5,475)	(4,418)
Transfers in	0	989	2,627	999
Transfers out		(2,948)	(9,196)	(7,910)
Ending balance	9,405	14,963	9,405	14,963
Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end	0	0	0	0
Corporate Debt | Net investment income
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	(37)	(52)	(111)	(125)
Corporate Debt | Net realized investment gains (losses)
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	0		(8)	13
Asset-backed Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation:
Beginning balance	9,420	3,005	4,986	3,007
Included in earnings, as a part of:
Included in other comprehensive income	15	(45)	(126)	(47)
Purchases	0	580	16,678	580
Sales	0	0	(185)	0
Transfers in	0	0	0	0
Transfers out	(2,277)	0	(14,196)	0
Ending balance	7,159	3,540	7,159	3,540
Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end	0	0	0	0
Asset-backed Securities | Net investment income
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	1	0	2	0
Asset-backed Securities | Net realized investment gains (losses)
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	0		0	0
Other investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation:
Beginning balance	5	5	409	3
Included in earnings, as a part of:
Included in other comprehensive income	0	0	0	140
Purchases	0	0	0	0
Sales	0	0	(366)	(912)
Transfers in	0	423	0	1,321
Transfers out	0	0	0	0
Ending balance	6	428	6	428
Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end	0	0	0	0
Other investments | Net investment income
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	0	$ 0	0	0
Other investments | Net realized investment gains (losses)
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	$ 1		$ (37)	$ (124)

Fair Value Measurement (Investm

Fair Value Measurement (Investments in LLCs and Limited Partnerships) (Details) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	$ 307,991,000	$ 230,889,000
Equities | Mortgage fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Commitments	0
Fair Value	20,416,000	0
Investment in unconsolidated subsidiaries
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	287,575,000	210,759,000
Investment in unconsolidated subsidiaries | Private debt funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Commitments	19,918,000
Fair Value	23,736,000	42,206,000
Investment in unconsolidated subsidiaries | Long equity fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Commitments	0
Fair Value	6,899,000	7,847,000
Investment in unconsolidated subsidiaries | Long/short equity funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Commitments	0
Fair Value	27,927,000	31,352,000
Investment in unconsolidated subsidiaries | Non-public equity funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Commitments	73,795,000
Fair Value	113,669,000	100,062,000
Investment in unconsolidated subsidiaries | Multi-strategy fund of funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Commitments	0
Fair Value	9,447,000	9,100,000
Investment in unconsolidated subsidiaries | Credit fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Commitments	8,916,000
Fair Value	29,485,000	6,561,000
Investment in unconsolidated subsidiaries | Long/short commodities fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Commitments	0
Fair Value	13,686,000	13,025,000
Investment in unconsolidated subsidiaries | Strategy focused fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Commitments	29,693,000
Fair Value	62,726,000	606,000
Other investments | Mortgage fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	$ 0	$ 20,130,000

Fair Value Measurement (Inves_2

Fair Value Measurement (Investments in LLCs and Limited Partnerships Footnote) (Details)	9 Months Ended
	Sep. 30, 2018
Mortgage fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investment redemption notice period	65 days
Payment period for redemption of LP valued at NAV	45 days
Secured debt fund | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Liquidating investments remaining period	3 years
Secured debt fund | Maximum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Liquidating investments remaining period	8 years
Long equity fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investment redemption notice period	15 days
Payment period for redemption of LP valued at NAV	10 days
Long/short equity funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Payment period for redemption of LP valued at NAV	30 days
Redemption percentage of LP at NAV for which initial payment is limited	90.00%
Long/short equity funds | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investment redemption notice period	30 days
Long/short equity funds | Maximum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investment redemption notice period	90 days
Non-public equity funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Liquidating investments remaining period	9 years
Credit fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investment redemption notice period, two funds	90 days
Investment redemption notice period, one fund	180 days
Long/short commodities fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investment redemption notice period	30 days
Long/short commodities fund | Maximum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Payment period for redemption of LP valued at NAV	30 days

Fair Value Measurement (Finanac

Fair Value Measurement (Finanacial Instruments Not Measured at Fair Value) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financial assets:
BOLI	$ 63,638	$ 62,113
Other investments	35,798	110,847
Other assets	110,475	101,428
Financial liabilities:
Other liabilities	179,534	437,600
Carrying Value | Not measured at fair value
Financial assets:
BOLI	63,638	62,113
Other investments	2,930	58,546
Other assets	38,405	34,020
Financial liabilities:
Other liabilities	23,186	21,154
Carrying Value | Not measured at fair value | Senior notes due 2023
Financial liabilities:
Debt	250,000	250,000
Carrying Value | Not measured at fair value | Revolving credit agreement
Financial liabilities:
Debt	0	123,000
Carrying Value | Not measured at fair value | Mortgage loans
Financial liabilities:
Debt	39,413	40,460
Fair Value | Not measured at fair value | Level 3
Financial assets:
BOLI	63,638	62,113
Other investments	2,930	69,095
Other assets	38,219	33,742
Financial liabilities:
Other liabilities	23,186	21,154
Fair Value | Not measured at fair value | Level 3 | Senior notes due 2023
Financial liabilities:
Debt	260,630	273,153
Fair Value | Not measured at fair value | Level 3 | Revolving credit agreement
Financial liabilities:
Debt	0	123,000
Fair Value | Not measured at fair value | Level 3 | Mortgage loans
Financial liabilities:
Debt	$ 39,413	$ 40,460

Investments (Narrative) (Detail

Investments (Narrative) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2018USD ($)Businessinvestment_interestIssuerSecurity	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)Businessinvestment_interestIssuerSecurity	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)IssuerSecurity
Reclassifications from AOCI to net income:
Securities on deposit with state insurance departments	$ 46,100,000		$ 46,100,000
Business owned life insurance cost	33,000,000		33,000,000
Investment in unconsolidated subsidiaries	$ 390,738,000		$ 390,738,000		$ 330,591,000
Number of LPs / LLCs with investment ownership percent over 25% (in businesses) | Business	1		1
Total OTTI losses:	$ (86,000)	$ 0	$ (490,000)	$ (419,000)
Net impairment losses recognized in earnings	86,000	0	490,000	171,000
Portion of noncredit OTTI losses recognized in OCI	$ 0	0	$ 0	(248,000)
Tax Credit Partnerships Almost 100% Ownership
Reclassifications from AOCI to net income:
Number of tax credit partnerships almost 100% ownership percentage | investment_interest	2		2
Investment in unconsolidated subsidiaries	$ 26,700,000		$ 26,700,000		32,500,000
Tax Credit Partnerships Almost 100% Ownership | Maximum
Reclassifications from AOCI to net income:
Investment ownership percentage	100.00%		100.00%
Tax Credit Partnerships Less Than 20% Ownership
Reclassifications from AOCI to net income:
Investment in unconsolidated subsidiaries	$ 43,500,000		$ 43,500,000		52,100,000
Tax Credit Partnerships Less Than 20% Ownership | Maximum
Reclassifications from AOCI to net income:
Investment ownership percentage	20.00%		20.00%
Other Limited Partnerships and Limited Liability Company, Greater Than 25% Ownership
Reclassifications from AOCI to net income:
Investment in unconsolidated subsidiaries	$ 24,100,000		$ 24,100,000		30,800,000
Other Limited Partnerships and Limited Liability Company Less than 25% Ownership
Reclassifications from AOCI to net income:
Investment in unconsolidated subsidiaries	292,000,000		292,000,000		$ 209,100,000
Fixed maturities
Reclassifications from AOCI to net income:
Required FAL deposit	124,700,000		124,700,000
Short-term investments
Reclassifications from AOCI to net income:
Required FAL deposit	$ 700,000		$ 700,000
Non government-backed
Reclassifications from AOCI to net income:
Debt securities in unrealized loss position (in securities) | Security	1,090		1,090		629
Debt securities in unrealized loss position as percentage of total debt securities held	52.20%		52.20%		26.50%
Issuers in unrealized loss position (in issuers) | Issuer	571		571		375
Single greatest unrealized loss position	$ 500,000		$ 500,000		$ 400,000
Second greatest unrealized loss position	400,000		400,000		$ 300,000
Corporate Debt
Reclassifications from AOCI to net income:
Total OTTI losses:	$ (86,000)	$ 0	$ (490,000)	(419,000)
Portion of noncredit OTTI losses recognized in OCI				$ (248,000)

Investments (Available-For-Sale

Investments (Available-For-Sale Fixed Maturities) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Reclassifications from AOCI to net income:
Amortized Cost	$ 2,159,719	$ 2,257,188
Gross Unrealized Gains	8,679	32,610
Gross Unrealized Losses	36,063	9,556
Estimated Fair Value	2,132,335	2,280,242
U.S. Treasury obligations
Reclassifications from AOCI to net income:
Amortized Cost	127,596	134,323
Gross Unrealized Gains	164	485
Gross Unrealized Losses	2,688	1,181
Estimated Fair Value	125,072	133,627
U.S. Government-sponsored enterprise obligations
Reclassifications from AOCI to net income:
Amortized Cost	36,768	21,089
Gross Unrealized Gains	12	73
Gross Unrealized Losses	898	206
Estimated Fair Value	35,882	20,956
State and municipal bonds
Reclassifications from AOCI to net income:
Amortized Cost	308,712	618,414
Gross Unrealized Gains	3,900	14,248
Gross Unrealized Losses	2,424	419
Estimated Fair Value	310,188	632,243
Corporate debt
Reclassifications from AOCI to net income:
Amortized Cost	1,258,709	1,157,660
Gross Unrealized Gains	3,752	15,205
Gross Unrealized Losses	21,149	5,707
Estimated Fair Value	1,241,312	1,167,158
Residential mortgage-backed securities
Reclassifications from AOCI to net income:
Amortized Cost	192,859	196,741
Gross Unrealized Gains	793	2,438
Gross Unrealized Losses	6,192	1,335
Estimated Fair Value	187,460	197,844
Agency commercial mortgage-backed securities
Reclassifications from AOCI to net income:
Amortized Cost	13,893	10,827
Gross Unrealized Gains	0	23
Gross Unrealized Losses	349	108
Estimated Fair Value	13,544	10,742
Agency commercial mortgage-backed securities
Reclassifications from AOCI to net income:
Amortized Cost	31,882	16,004
Gross Unrealized Gains	35	91
Gross Unrealized Losses	506	134
Estimated Fair Value	31,411	15,961
Other asset-backed securities
Reclassifications from AOCI to net income:
Amortized Cost	189,300	102,130
Gross Unrealized Gains	23	47
Gross Unrealized Losses	1,857	466
Estimated Fair Value	$ 187,466	$ 101,711

Investments (Available-For-Sa_2

Investments (Available-For-Sale Securities by Contractual Maturity) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Reclassifications from AOCI to net income:
Amortized Cost	$ 2,159,719	$ 2,257,188
Total Fair Value	2,132,335	2,280,242
U.S. Treasury obligations
Reclassifications from AOCI to net income:
Amortized Cost	127,596	134,323
Due in one year or less	27,456
Due after one year through five years	76,463
Due after five years through ten years	18,501
Due after ten years	2,652
Total Fair Value	125,072	133,627
U.S. Government-sponsored enterprise obligations
Reclassifications from AOCI to net income:
Amortized Cost	36,768	21,089
Due in one year or less	3,276
Due after one year through five years	12,973
Due after five years through ten years	19,502
Due after ten years	131
Total Fair Value	35,882	20,956
State and municipal bonds
Reclassifications from AOCI to net income:
Amortized Cost	308,712	618,414
Due in one year or less	26,232
Due after one year through five years	108,583
Due after five years through ten years	144,847
Due after ten years	30,526
Total Fair Value	310,188	632,243
Corporate debt
Reclassifications from AOCI to net income:
Amortized Cost	1,258,709	1,157,660
Due in one year or less	144,784
Due after one year through five years	714,013
Due after five years through ten years	352,691
Due after ten years	29,824
Total Fair Value	1,241,312	1,167,158
Residential mortgage-backed securities
Reclassifications from AOCI to net income:
Amortized Cost	192,859	196,741
Total Fair Value	187,460	197,844
Agency commercial mortgage-backed securities
Reclassifications from AOCI to net income:
Amortized Cost	13,893	10,827
Total Fair Value	13,544	10,742
Other commercial mortgage-backed securities
Reclassifications from AOCI to net income:
Amortized Cost	31,882	16,004
Total Fair Value	31,411	15,961
Other asset-backed securities
Reclassifications from AOCI to net income:
Amortized Cost	189,300	102,130
Total Fair Value	$ 187,466	$ 101,711

Investments (Investments Held i

Investments (Investments Held in a Loss Position) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair Value
Fair Value	$ 1,632,392	$ 850,838
Less than 12 Months, Fair Value	1,214,034	603,468
More than 12 Months, Fair Value	418,358	247,370
Unrealized Loss
Unrealized Loss	36,063	9,556
Less than 12 Months, Unrealized Loss	20,944	4,314
More than 12 Months, Unrealized Loss	15,119	5,242
U.S. Treasury obligations
Fair Value
Fair Value	118,159	110,788
Less than 12 Months, Fair Value	62,352	67,135
More than 12 Months, Fair Value	55,807	43,653
Unrealized Loss
Unrealized Loss	2,688	1,181
Less than 12 Months, Unrealized Loss	1,020	554
More than 12 Months, Unrealized Loss	1,668	627
U.S. Government-sponsored enterprise obligations
Fair Value
Fair Value	34,713	17,032
Less than 12 Months, Fair Value	22,082	10,182
More than 12 Months, Fair Value	12,631	6,850
Unrealized Loss
Unrealized Loss	898	206
Less than 12 Months, Unrealized Loss	364	64
More than 12 Months, Unrealized Loss	534	142
State and municipal bonds
Fair Value
Fair Value	134,549	23,122
Less than 12 Months, Fair Value	125,853	15,168
More than 12 Months, Fair Value	8,696	7,954
Unrealized Loss
Unrealized Loss	2,424	419
Less than 12 Months, Unrealized Loss	2,135	102
More than 12 Months, Unrealized Loss	289	317
Corporate debt
Fair Value
Fair Value	967,853	487,578
Less than 12 Months, Fair Value	746,194	365,541
More than 12 Months, Fair Value	221,659	122,037
Unrealized Loss
Unrealized Loss	21,149	5,707
Less than 12 Months, Unrealized Loss	13,342	2,730
More than 12 Months, Unrealized Loss	7,807	2,977
Residential mortgage-backed securities
Fair Value
Fair Value	167,145	109,659
Less than 12 Months, Fair Value	92,516	64,121
More than 12 Months, Fair Value	74,629	45,538
Unrealized Loss
Unrealized Loss	6,192	1,335
Less than 12 Months, Unrealized Loss	2,348	402
More than 12 Months, Unrealized Loss	3,844	933
Agency commercial mortgage-backed securities
Fair Value
Fair Value	13,544	4,423
Less than 12 Months, Fair Value	9,416	2,458
More than 12 Months, Fair Value	4,128	1,965
Unrealized Loss
Unrealized Loss	349	108
Less than 12 Months, Unrealized Loss	105	34
More than 12 Months, Unrealized Loss	244	74
Other commercial mortgage-backed securities
Fair Value
Fair Value	29,076	12,878
Less than 12 Months, Fair Value	24,184	7,939
More than 12 Months, Fair Value	4,892	4,939
Unrealized Loss
Unrealized Loss	506	134
Less than 12 Months, Unrealized Loss	322	82
More than 12 Months, Unrealized Loss	184	52
Other asset-backed securities
Fair Value
Fair Value	167,353	85,358
Less than 12 Months, Fair Value	131,437	70,924
More than 12 Months, Fair Value	35,916	14,434
Unrealized Loss
Unrealized Loss	1,857	466
Less than 12 Months, Unrealized Loss	1,308	346
More than 12 Months, Unrealized Loss	$ 549	$ 120

Investments (Sales and Purchase

Investments (Sales and Purchases of Available-for-Sale Securities) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Information regarding sales and purchases of available-for-sale securities
Proceeds from sales (exclusive of maturities and paydowns)	$ 61,300	$ 74,100	$ 556,300	$ 309,600
Purchases	$ 164,600	$ 90,600	$ 717,119	$ 449,717

Investments (Net Investment Inc

Investments (Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Net Investment Income
Investment fees and expenses	$ (1,600)	$ (1,457)	$ (5,183)	$ (5,173)
Net investment income	23,266	23,729	67,677	69,592
Fixed maturities
Net Investment Income
Investment Income	17,228	18,924	51,814	57,885
Equities
Net Investment Income
Investment Income	5,687	4,495	15,553	12,437
Short-term investments, including Other
Net Investment Income
Investment Income	1,330	1,147	3,968	2,926
BOLI
Net Investment Income
Investment Income	$ 621	$ 620	$ 1,525	$ 1,517

Investments (Unconsolidated Sub

Investments (Unconsolidated Subsidiaries) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Unconsolidated Subsidiaries
Investment in unconsolidated subsidiaries	$ 390,738	$ 330,591
Qualified affordable housing project tax credit partnerships
Unconsolidated Subsidiaries
Investment in unconsolidated subsidiaries	70,217	84,607
Other tax credit partnerships
Unconsolidated Subsidiaries
Investment in unconsolidated subsidiaries	4,414	6,118
All other investments, primarily investment fund LPs/LLCs
Unconsolidated Subsidiaries
Investment in unconsolidated subsidiaries	$ 316,107	$ 239,866

Investments (Equity in Earnings

Investments (Equity in Earnings (Loss) of Unconsolidated Subsidiaries) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Investments, Debt and Equity Securities [Abstract]
Losses recorded from affordable housing projects	$ 4,661	$ 3,442	$ 14,373	$ 10,713
Tax credits recognized related to affordable housing projects	4,618	4,608	13,855	13,833
Losses from historic tax credit investments	1,394	621	4,776	3,388
Tax credits recognized related to historic tax credit investments	$ 570	$ 1,352	$ 1,925	$ 3,976

Investments (Net Realized Inves

Investments (Net Realized Investment Gains (Losses)) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Marketable Securities [Line Items]
Total OTTI losses:	$ (86,000)	$ 0	$ (490,000)	$ (419,000)
Portion of OTTI losses recognized in other comprehensive income before taxes	0	0	0	248,000
Net impairment losses recognized in earnings	(86,000)	0	(490,000)	(171,000)
Gross realized gains, available-for-sale fixed maturities	690,000	1,724,000	5,592,000	4,323,000
Gross realized (losses), available-for-sale fixed maturities	(1,400,000)	(262,000)	(5,172,000)	(1,730,000)
Net realized gains (losses), short-term investments	0	(1,000)	0	(1,000)
Net realized gains (losses), trading fixed maturities	(28,000)	0	(100,000)	0
Net realized gains (losses), equity investments	4,689,000	3,603,000	17,395,000	10,958,000
Net realized gains (losses), other investments	561,000	478,000	1,652,000	2,197,000
Change in unrealized holding gains (losses), trading fixed maturities	(42,000)	0	(261,000)	0
Change in unrealized holding gains (losses), equity investments	7,996,000	2,182,000	(15,104,000)	2,606,000
Change in unrealized holding gains (losses), convertible securities, carried at fair value	(260,000)	23,000	(1,126,000)	621,000
Other	253,000	2,000	265,000	7,000
Total net realized investment gains (losses)	12,373,000	7,749,000	2,651,000	18,810,000
Corporate Debt
Marketable Securities [Line Items]
Total OTTI losses:	$ (86,000)	$ 0	$ (490,000)	(419,000)
Portion of OTTI losses recognized in other comprehensive income before taxes				$ 248,000

Investments (Credit Losses Reco

Investments (Credit Losses Recorded in Earnings) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Other than Temporary Impairment, Credit Losses Recognized in Earnings:
Balance beginning of period	$ 1,313	$ 1,313	$ 1,313	$ 1,158
No OTTI has been previously recognized	0	0	0	171
Securities sold during the period (realized)	(1,220)	0	(1,220)	(16)
Balance ending of period	$ 93	$ 1,313	$ 93	$ 1,313

Retroactive Insurance Contrac_2

Retroactive Insurance Contracts (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Net premiums earned	$ 206,070	$ 192,303	$ 616,819	$ 555,559
Net losses and loss adjustment expenses	147,605	129,356	439,120	364,058
Reserve for losses and loss adjustment expenses	$ 2,099,827	$ 2,040,698	2,099,827	$ 2,040,698		$ 2,048,381	$ 1,993,428
Retroactive Insurance Contract
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Net premiums earned			26,600
Net losses and loss adjustment expenses			25,400
Reserve for losses and loss adjustment expenses					$ 600
Retroactive Insurance Contract, Prospective Coverage
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Net premiums earned			7,900
Retroactive Insurance Contract, Retroactive Coverage
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Net premiums earned			$ 18,700

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income taxes liabilities	$ 2.1	$ 8
Unrecognized tax benefits	5.1	5.8
Accrued liability for interest related to unrecognized tax benefits	$ 0.6	$ 0.5

Reserve for Losses and Loss A_3

Reserve for Losses and Loss Adjustment Expenses (Details) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2018USD ($)partition	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)
Liability for Claims and Claims Adjustment Expense [Line Items]
Minimum period for claims resolution (years)	5 years
Number of business partitions (in partitions) | partition	200
Summary of reserve for losses and loss adjustment expenses
Balance, beginning of year	$ 2,048,381	$ 1,993,428	$ 1,993,428
Less reinsurance recoverables on unpaid losses and loss adjustment expenses	335,585	273,475	273,475
Net balance, beginning of year	1,712,796	1,719,953	1,719,953
Net losses:
Current year	506,269	454,121	603,518
Favorable development of reserves established in prior years, net	(67,149)	(90,063)	(134,360)
Total	439,120	364,058	469,158
Paid related to:
Current year	(69,881)	(63,667)	(106,633)
Prior years	(314,763)	(293,522)	(369,682)
Total paid	(384,644)	(357,189)	(476,315)
Net balance, end of period	1,767,272	1,726,822	1,712,796
Plus reinsurance recoverables on unpaid losses and loss adjustment expenses	332,555	313,876	335,585
Balance, end of period	2,099,827	$ 2,040,698	$ 2,048,381
Retroactive Insurance Contract
Net losses:
Current year	$ 25,400

Commitments and Contingencies (

Commitments and Contingencies (Details) $ in Millions	Sep. 30, 2018USD ($)	Sep. 30, 2018GBP (£)	Feb. 28, 2018GBP (£)	Jan. 31, 2018GBP (£)
Lloyd's Syndicates
Other Commitments [Line Items]
Required FAL deposit	$ 125.4
Current lending capacity under revolving credit agreement | £			£ 30,000,000	£ 20,000,000
Interest rate on revolving credit agreement (percent)	3.80%	3.80%
Unused commitments to extend credit	$ 11.5	£ 8,800,000
Commitment to provide capital | Lloyd's Syndicates
Other Commitments [Line Items]
Commitments total	200
Funding Commitments
Other Commitments [Line Items]
Commitments total	$ 272.1

Debt (Details)

Debt (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Gross debt	$ 289,413,000	$ 413,460,000
Less debt issuance costs	1,399,000	1,649,000
Debt less debt issuance costs	288,014,000	411,811,000
Senior notes due 2023 | Senior notes due 2023
Debt Instrument [Line Items]
Gross debt	$ 250,000,000	$ 250,000,000
Stated interest rate on debt	5.30%	5.30%
Revolving credit agreement | Revolving credit agreement
Debt Instrument [Line Items]
Gross debt	$ 0	$ 123,000,000
Weighted average interest rate on debt		1.91%
Line of credit maximum borrowing capacity	250,000,000	$ 250,000,000
Mortgage loans
Debt Instrument [Line Items]
Gross debt	$ 39,413,000	$ 40,460,000
Stated interest rate on debt	3.66%	2.86%
Mortgage loans | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate for debt	1.325%	1.325%

Derivatives (Narrative) (Detail

Derivatives (Narrative) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Mortgage loans | LIBOR
Derivative [Line Items]
Basis spread on variable rate for debt	1.325%	1.325%
Interest Rate Cap
Derivative [Line Items]
Premium paid on derivative for right to receive cash payments		$ 2,000
Floor interest rate on derivative	2.35%
Cap interest rate on derivative	3.675%
Interest Rate Cap | Other assets
Derivative [Line Items]
Derivative asset, notional amount	$ 35,000	$ 35,000

Derivatives (Volume and Fair Va

Derivatives (Volume and Fair Value) (Details) - Interest Rate Cap - Other assets $ in Thousands	Sep. 30, 2018USD ($)derivative_instrument	Dec. 31, 2017USD ($)derivative_instrument
Derivative [Line Items]
Number of instruments (in derivative instruments) | derivative_instrument	1	1
Notional amount	$ 35,000	$ 35,000
Estimated fair value	$ 2,852	$ 1,731

Derivatives (Pre-tax Impact of

Derivatives (Pre-tax Impact of Change in Fair Value) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Interest Rate Cap | Interest expense
Derivative [Line Items]
Gains (Losses) Recognized in Income on Derivatives	$ 264	$ 0	$ 1,121	$ 0

Shareholders' Equity (Narrative

Shareholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended						9 Months Ended		12 Months Ended
	Feb. 28, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2015	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorized common stock (in shares)		100,000,000						100,000,000			100,000,000
Authorized preferred stock (in shares)		50,000,000						50,000,000			50,000,000
Quarterly dividend declared, per share (in usd per share)		$ 0.31	$ 0.31	$ 0.310	$ 0.31	$ 0.31	$ 0.310	$ 0.93	$ 0.93
Dividend declared								$ 50.9	$ 49.6
Total authorizations which remain available for use		$ 109.6						$ 109.6
Common shares acquired (in shares)								0	0
Bonus compensation shares issued (in shares)	2,500
Non-credit loss, net of tax		$ 0.1						$ 0.1			$ 0.5
Accumulated Other Comprehensive Income (Loss)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reclassification from AOCI to retained earnings for stranded tax effects								3.4
Retained Earnings
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reclassification from AOCI to retained earnings for stranded tax effects								$ (3.4)
Restricted Share Units (in shares)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards in period (in shares)	85,800
Fair value of each unit awarded (in usd per share)	$ 44.73
Award vesting period								3 years
Shares issued in period for share-based compensation (in shares)	52,800
Performance Share Units (in shares)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards in period (in shares)	27,200
Shares issued in period for share-based compensation (in shares)	80,600
Performance Share Units (in shares) | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award payout rate								50.00%
Performance Share Units (in shares) | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award payout rate								200.00%
Level at which performance shares were granted in 2015 | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award payout rate										125.00%

Shareholders' Equity (Share-bas

Shareholders' Equity (Share-based Compensation Expense and Related Tax Benefits) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Equity [Abstract]
Share-based compensation expense	$ 1,628	$ 1,018	$ 4,145	$ 7,110
Related tax benefits	$ 342	$ 356	$ 870	$ 2,489

Shareholders' Equity (AOCI Recl

Shareholders' Equity (AOCI Reclassification) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reclassifications from AOCI to net income:
Reclassifications from AOCI to net income:	$ (796)	$ 1,462	$ (70)	$ 2,422
Tax effect	167	(512)	15	(848)
Net reclassification adjustments	(629)	950	(55)	1,574
Deferred tax expense (benefit) included in OCI	(1,197)	(373)	(10,442)	4,091
Realized investment gains (losses)
Reclassifications from AOCI to net income:
Reclassifications from AOCI to net income:	(175)	1,462	551	2,425
Non-credit impairment losses reclassified to earnings, due to sale of securities or reclassification as a credit loss
Reclassifications from AOCI to net income:
Reclassifications from AOCI to net income:	$ (621)	$ 0	$ (621)	$ (3)

Variable Interest Entities (Det

Variable Interest Entities (Details) $ in Millions	Sep. 30, 2018USD ($)
Variable interest entity, not primary beneficiary | Investment in unconsolidated subsidiaries
Variable Interest Entity [Line Items]
VIE interests carrying value	$ 304.7

Earnings Per Share (Details)

Earnings Per Share (Details) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average number of common shares outstanding, basic (in shares)	53,620,000	53,413,000	53,585,000	53,377,000
Weighted average number of common shares outstanding, diluted (in shares)	53,773,000	53,614,000	53,735,000	53,586,000
Effect of dilutive shares on earnings per share (in usd per share)	$ 0	$ 0	$ 0	$ 0
Antidilutive shares excluded from computation of earnings per share (in shares)	0	28,000	3,000	9,000
Restricted Share Units (in shares)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dilutive securities (in shares)	83,000	87,000	78,000	81,000
Performance Share Units (in shares)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dilutive securities (in shares)	48,000	88,000	52,000	105,000
Purchase Match Units (in shares)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dilutive securities (in shares)	22,000	26,000	20,000	23,000

Segment Information (Narrative)

Segment Information (Narrative) (Details)	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Workers' Compensation Insurance
Segment Reporting Information [Line Items]
Worker's compensation SPC percentage ceded	100.00%
Syndicate 1,729
Segment Reporting Information [Line Items]
Proportion of capital provided to support Lloyd's Syndicate 1729		62.00%	58.00%
Syndicate 6,131
Segment Reporting Information [Line Items]
Proportion of capital provided to support Lloyd's Syndicate 1729		100.00%

Segment Information (Financial

Segment Information (Financial Data by Segment) (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Net premiums earned	$ 206,070	$ 192,303		$ 616,819	$ 555,559
Net investment income	23,266	23,729		67,677	69,592
Equity in earnings (loss) of unconsolidated subsidiaries	5,228	4,164		12,247	8,489
Net realized gains (losses)	12,373	7,749		2,651	18,810
Other income (expense)	2,388	510		7,155	4,581
Net losses and loss adjustment expenses	(147,605)	(129,356)		(439,120)	(364,058)
Underwriting, policy acquisition and operating expenses	(61,844)	(57,111)		(178,812)	(172,106)
Segregated portfolio cells dividend (expense) income	(5,255)	(2,891)		(9,787)	(14,076)
Interest expense	(3,599)	(4,124)		(11,262)	(12,402)
Income tax benefit (expense)	206	(6,024)		3,939	(4,467)
Net income	31,228	28,949		71,507	89,922
Depreciation and amortization, net of accretion	5,506	7,075		16,544	21,024
Pre-tax expense	31,022	34,973		67,568	94,389
Tax impact	(206)	6,024		(3,939)	4,467
Specialty P&C
Segment Reporting Information [Line Items]
Net premiums earned	120,789	117,288		378,355	337,287
Workers' Compensation Insurance
Segment Reporting Information [Line Items]
Net premiums earned	47,296	41,540		135,230	122,247
Segregated Portfolio Cell Reinsurance
Segment Reporting Information [Line Items]
Net premiums earned	18,963	17,157		54,247	50,651
Lloyd's Syndicates
Segment Reporting Information [Line Items]
Net premiums earned	19,022	16,318		48,987	45,374
Operating segments | Specialty P&C
Segment Reporting Information [Line Items]
Net premiums earned	120,789	117,288		378,355	337,287
Net investment income	0	0		0	0
Equity in earnings (loss) of unconsolidated subsidiaries	0	0		0	0
Net realized gains (losses)	0	0		0	0
Other income (expense)	1,426	1,276		3,945	3,943
Net losses and loss adjustment expenses	(98,363)	(72,944)		(292,742)	(217,512)
Underwriting, policy acquisition and operating expenses	(27,931)	(26,816)		(83,833)	(78,601)
Segregated portfolio cells dividend (expense) income	0	0		0	(5,181)
Interest expense	0			0	0
Income tax benefit (expense)	0			0	0
Net income	(4,079)	18,804		5,725	39,936
Depreciation and amortization, net of accretion	1,715	1,933		5,343	5,350
Tax impact	0			0	0
Operating segments | Workers' Compensation Insurance
Segment Reporting Information [Line Items]
Net premiums earned	47,296	41,540		135,230	122,247
Net investment income	0	0		0	0
Equity in earnings (loss) of unconsolidated subsidiaries	0	0		0	0
Net realized gains (losses)	0	0		0	0
Other income (expense)	376	535		1,828	1,716
Net losses and loss adjustment expenses	(30,650)	(27,065)		(87,794)	(79,520)
Underwriting, policy acquisition and operating expenses	(15,410)	(13,912)		(41,545)	(38,912)
Segregated portfolio cells dividend (expense) income	0	0		0	0
Interest expense	0	0		0	0
Income tax benefit (expense)	0	0		0	0
Net income	1,612	1,098		7,719	5,531
Depreciation and amortization, net of accretion	959	848		2,873	2,516
Tax impact	0	0		0	0
Operating segments | Segregated Portfolio Cell Reinsurance
Segment Reporting Information [Line Items]
Net premiums earned	18,963	17,157		54,247	50,651
Net investment income	371	290		1,100	742
Equity in earnings (loss) of unconsolidated subsidiaries	0	0		0	0
Net realized gains (losses)	1,397	944		467	2,715
Other income (expense)	86	33		176	83
Net losses and loss adjustment expenses	(8,560)	(8,903)		(27,561)	(26,308)
Underwriting, policy acquisition and operating expenses	(5,516)	(5,147)		(16,070)	(15,239)
Segregated portfolio cells dividend (expense) income	(5,255)	(2,891)		(9,787)	(8,895)
Interest expense	0	0		0	0
Income tax benefit (expense)	0	0		0	0
Net income	1,486	1,483		2,572	3,749
Depreciation and amortization, net of accretion	83	176		393	500
Tax impact	0	0		0	0
Operating segments | Lloyd's Syndicates
Segment Reporting Information [Line Items]
Net premiums earned	19,022	16,318		48,987	45,374
Net investment income	783	412		2,370	1,194
Equity in earnings (loss) of unconsolidated subsidiaries	0	0		0	0
Net realized gains (losses)	(98)	31		(404)	105
Other income (expense)	352	(1,881)		247	(1,641)
Net losses and loss adjustment expenses	(10,032)	(20,444)		(31,023)	(40,718)
Underwriting, policy acquisition and operating expenses	(8,439)	(6,723)		(23,745)	(19,786)
Segregated portfolio cells dividend (expense) income	0	0		0	0
Interest expense	0	0		0	0
Income tax benefit (expense)	361	(61)		355	495
Net income	1,949	(12,348)		(3,213)	(14,977)
Depreciation and amortization, net of accretion	(2)	(6)		(5)	(14)
Tax impact	(361)	61		(355)	(495)
Operating segments | Corporate
Segment Reporting Information [Line Items]
Net premiums earned	0	0		0	0
Net investment income	22,112	23,027		64,207	67,656
Equity in earnings (loss) of unconsolidated subsidiaries	5,228	4,164		12,247	8,489
Net realized gains (losses)	11,074	6,774		2,588	15,990
Other income (expense)	699	1,023		2,737	1,974
Net losses and loss adjustment expenses	0	0		0	0
Underwriting, policy acquisition and operating expenses	(5,053)	(4,989)		(15,351)	(21,062)
Segregated portfolio cells dividend (expense) income	0	0		0	0
Interest expense	(3,645)	(4,124)		(11,308)	(12,402)
Income tax benefit (expense)	(155)	(5,963)		3,584	(4,962)
Net income	30,260	19,912		58,704	55,683
Depreciation and amortization, net of accretion	2,751	4,124		7,940	12,672
Tax impact	155	5,963		(3,584)	4,962
Inter-segment Eliminations
Segment Reporting Information [Line Items]
Net premiums earned	0	0		0	0
Net investment income	0	0		0	0
Equity in earnings (loss) of unconsolidated subsidiaries	0	0		0	0
Net realized gains (losses)	0	0		0	0
Other income (expense)	(551)	(476)		(1,778)	(1,494)
Net losses and loss adjustment expenses	0	0		0	0
Underwriting, policy acquisition and operating expenses	505	476		1,732	1,494
Segregated portfolio cells dividend (expense) income	0	0		0	0
Interest expense	46	0		46	0
Income tax benefit (expense)	0			0	0
Net income	0	0		0	0
Depreciation and amortization, net of accretion	0	$ 0		0	0
Tax impact	$ 0			$ 0	$ 0
Previously unrecognized segregated portfolio cells (SPC) dividend expense | Operating segments | Specialty P&C
Segment Reporting Information [Line Items]
Pre-tax expense			$ 5,200
Previously unrecognized segregated portfolio cells (SPC) dividend expense | Operating segments | Corporate
Segment Reporting Information [Line Items]
Income tax benefit (expense)			(1,800)
Tax impact			$ 1,800

Segment Information (Gross Prem

Segment Information (Gross Premiums Earned and Reconciliation to Net Premiums) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Segment net premiums earned	$ 206,070	$ 192,303	$ 616,819	$ 555,559
Healthcare professional liability
Segment Reporting Information [Line Items]
Gross premiums earned	1,225		3,782
Specialty P&C
Segment Reporting Information [Line Items]
Ceded premiums earned	(21,022)	(23,139)	(58,753)	(65,610)
Segment net premiums earned	120,789	117,288	378,355	337,287
Specialty P&C | Healthcare professional liability
Segment Reporting Information [Line Items]
Gross premiums earned	126,012	125,377	390,904	358,209
Specialty P&C | Legal professional liability
Segment Reporting Information [Line Items]
Gross premiums earned	6,606	6,483	19,486	19,217
Specialty P&C | Medical technology liability
Segment Reporting Information [Line Items]
Gross premiums earned	9,080	8,459	26,372	25,160
Specialty P&C | Other
Segment Reporting Information [Line Items]
Gross premiums earned	113	108	346	311
Traditional business
Segment Reporting Information [Line Items]
Gross premiums earned	50,271	43,734	145,334	128,203
Alternative market business
Segment Reporting Information [Line Items]
Gross premiums earned	21,564	20,200	61,593	59,855
Workers' Compensation Insurance
Segment Reporting Information [Line Items]
Ceded premiums earned	(24,539)	(22,394)	(71,697)	(65,811)
Segment net premiums earned	47,296	41,540	135,230	122,247
Segregated Portfolio Cell Reinsurance
Segment Reporting Information [Line Items]
Gross premiums earned		1,044		3,106
Ceded premiums earned	(2,513)	(2,183)	(6,822)	(6,471)
Segment net premiums earned	18,963	17,157	54,247	50,651
Segregated Portfolio Cell Reinsurance | Traditional business
Segment Reporting Information [Line Items]
Gross premiums earned	20,251	18,296	57,287	54,016
Lloyd's Syndicates
Segment Reporting Information [Line Items]
Gross premiums earned	23,050	18,790	60,289	52,935
Ceded premiums earned	(4,028)	(2,472)	(11,302)	(7,561)
Segment net premiums earned	19,022	16,318	48,987	45,374
Premiums assumed under Quota Share Agreement	$ 1,200	$ 2,900	$ 4,500	$ 9,500

Subsequent Events (Details)

Subsequent Events (Details) - Subsequent event - Data analytics and services $ in Millions	1 Months Ended
	Oct. 31, 2018USD ($)
Agreement period of commitment	2 years
Annual fee	$ 5