ProAssurance (PRA) 10-K 21 Feb 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2018	Feb. 15, 2019	Jun. 30, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	PROASSURANCE CORP
Entity Central Index Key	1,127,703
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Amendment Flag	false
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Shell Company	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		53,640,178
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 1,865,211,215

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Investments
Fixed maturities, at fair value; cost or amortized cost, $2,155,270 and $2,257,188, respectively	$ 2,131,986	$ 2,280,242
Equity investments, at fair value; cost, $450,931 and $425,942, respectively	442,937	470,609
Short-term investments	308,319	432,126
Business owned life insurance	64,096	62,113
Investment in unconsolidated subsidiaries	367,757	330,591
Other investments, $31,344 and $52,301 at fair value, respectively, otherwise at cost or amortized cost	34,287	110,847
Total Investments	3,349,382	3,686,528
Cash and cash equivalents	80,471	134,495
Premiums receivable	261,466	238,085
Receivable from reinsurers on paid losses and loss adjustment expenses	11,558	7,317
Receivable from reinsurers on unpaid losses and loss adjustment expenses	343,820	335,585
Prepaid reinsurance premiums	40,631	39,916
Deferred policy acquisition costs	54,116	50,261
Deferred tax asset, net	29,108	9,930
Real estate, net	31,114	31,975
Intangible assets, net	76,776	82,952
Goodwill	210,725	210,725
Other assets	111,559	101,428
Total Assets	4,600,726	4,929,197
Policy liabilities and accruals
Reserve for losses and loss adjustment expenses	2,119,847	2,048,381
Unearned premiums	415,211	398,884
Reinsurance premiums payable	55,614	37,726
Total Policy Liabilities	2,590,672	2,484,991
Other liabilities	199,295	437,600
Debt less debt issuance costs	287,757	411,811
Total Liabilities	3,077,724	3,334,402
Shareholders’ Equity:
Common shares, par value $0.01 per share, 100,000,000 shares authorized, 62,989,421 and 62,824,523 shares issued, respectively	630	628
Additional paid-in capital	384,713	383,077
Accumulated other comprehensive income (loss), net of deferred tax expense (benefit) of ($4,355) and $5,218, respectively	(16,911)	14,911
Retained earnings	1,571,847	1,614,186
Treasury shares, at cost, 9,352,373 shares and 9,367,502 shares, respectively	(417,277)	(418,007)
Total Shareholders’ Equity	1,523,002	1,594,795
Total Liabilities and Shareholders' Equity	$ 4,600,726	$ 4,929,197

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Fixed maturities, available for sale, at fair value; amortized cost	$ 2,155,270	$ 2,257,188
Equity Investments, fair value, cost	450,931	425,942
Other investments, portion carried at fair value	$ 31,344	$ 52,301
Common shares, par value (USD per share)	$ 0.01	$ 0.01
Common shares authorized (shares)	100,000,000	100,000,000
Common shares, shares issued (shares)	62,989,421	62,824,523
Deferred tax expense (benefit) on accumulated other comprehensive income (loss)	$ (4,355)	$ 5,218
Treasury shares, number of shares (shares)	9,352,373	9,367,502

Consolidated Statements of Chan

Consolidated Statements of Changes in Capital - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Increase (Decrease) in Stockholders' Equity:
Beginning Balance		$ 1,594,795		$ 1,798,702	$ 1,594,795	$ 1,798,702	$ 1,958,354
Common shares reacquired							(2,106)
Common shares issued for compensation and effect of shares reissued to stock purchase plan					1,044	2,880	3,432
Share-based compensation					5,258	10,615	12,455
Net effect of restricted and performance shares issued					(3,934)	(5,437)	(3,030)
Dividends to shareholders					(94,314)	(316,890)	(315,028)
Other comprehensive income (loss)					(35,238)	(2,488)	(6,456)
Net income	$ (24,450)	11,856	$ 17,342	41,455	47,057	107,264	151,081
Ending Balance	1,523,002		1,594,795		1,523,002	1,594,795	1,798,702
Accounting Standards Update 2016-09
Increase (Decrease) in Stockholders' Equity:
Cumulative-effect adjustment ASU adoption							149
Accounting Standards Update 2016-01
Increase (Decrease) in Stockholders' Equity:
Cumulative-effect adjustment ASU adoption			8,334			8,334
Common Stock
Increase (Decrease) in Stockholders' Equity:
Beginning Balance		628		627	628	627	625
Net effect of restricted and performance shares issued					2	1	2
Ending Balance	630		628		630	628	627
Additional Paid-in Capital
Increase (Decrease) in Stockholders' Equity:
Beginning Balance		383,077		376,518	383,077	376,518	365,399
Common shares issued for compensation and effect of shares reissued to stock purchase plan					314	957	1,696
Share-based compensation					5,258	10,615	12,455
Net effect of restricted and performance shares issued					(3,936)	(5,438)	(3,032)
Ending Balance	384,713		383,077		384,713	383,077	376,518
Additional Paid-in Capital | Accounting Standards Update 2016-09
Increase (Decrease) in Stockholders' Equity:
Cumulative-effect adjustment ASU adoption							425
Additional Paid-in Capital | Accounting Standards Update 2016-01
Increase (Decrease) in Stockholders' Equity:
Cumulative-effect adjustment ASU adoption			0			0
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity:
Beginning Balance		14,911		17,399	14,911	17,399	23,855
Other comprehensive income (loss)					(35,238)	(2,488)	(6,456)
Ending Balance	(16,911)		14,911		(16,911)	14,911	17,399
Accumulated Other Comprehensive Income (Loss) | Accounting Standards Update 2018-02
Increase (Decrease) in Stockholders' Equity:
Cumulative-effect adjustment ASU adoption			3,416			3,416
Retained Earnings
Increase (Decrease) in Stockholders' Equity:
Beginning Balance		1,614,186		1,824,088	1,614,186	1,824,088	1,988,035
Dividends to shareholders					(94,314)	(316,890)	(315,028)
Net income					47,057	107,264	151,081
Ending Balance	1,571,847		1,614,186		1,571,847	1,614,186	1,824,088
Retained Earnings | Accounting Standards Update 2016-09
Increase (Decrease) in Stockholders' Equity:
Cumulative-effect adjustment ASU adoption							(276)
Retained Earnings | Accounting Standards Update 2016-01
Increase (Decrease) in Stockholders' Equity:
Cumulative-effect adjustment ASU adoption			8,334			8,334
Retained Earnings | Accounting Standards Update 2018-02
Increase (Decrease) in Stockholders' Equity:
Cumulative-effect adjustment ASU adoption			(3,416)			(3,416)
Treasury Stock
Increase (Decrease) in Stockholders' Equity:
Beginning Balance		$ (418,007)		$ (419,930)	(418,007)	(419,930)	(419,560)
Common shares reacquired							(2,106)
Common shares issued for compensation and effect of shares reissued to stock purchase plan					730	1,923	1,736
Ending Balance	$ (417,277)		$ (418,007)		$ (417,277)	$ (418,007)	$ (419,930)

Consolidated Statements of Inco

Consolidated Statements of Income and Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues
Net premiums earned	$ 818,853	$ 738,531	$ 733,281
Net investment income	91,884	95,662	100,012
Equity in earnings (loss) of unconsolidated subsidiaries	8,948	8,033	(5,762)
Net realized investment gains (losses):
OTTI losses	(490)	(13,200)	(10,834)
Portion of OTTI losses recognized in other comprehensive income before taxes	0	248	1,068
Net impairment losses recognized in earnings	(490)	(12,952)	(9,766)
Other net realized investment gains (losses)	(42,998)	29,361	44,641
Total net realized investment gains (losses)	(43,488)	16,409	34,875
Other income	9,833	7,514	7,808
Total revenues	886,030	866,149	870,214
Expenses
Net losses and loss adjustment expenses	593,210	469,158	443,229
Underwriting, policy acquisition and operating expenses
Operating expense	134,055	140,002	139,232
DPAC Amortization	104,501	95,751	88,378
Segregated portfolio cells dividend expense (income)	9,122	15,771	8,142
Interest expense	16,117	16,844	15,032
Total expenses	857,005	737,526	694,013
Income before income taxes	29,025	128,623	176,201
Provision for income taxes
Current expense (benefit)	(6,208)	19,666	16,586
Deferred expense (benefit)	(11,824)	1,693	8,534
Total income tax expense (benefit)	(18,032)	21,359	25,120
Segment operating results	47,057	107,264	151,081
Other comprehensive income (loss)	(35,238)	(2,488)	(6,456)
Comprehensive income (loss)	$ 11,819	$ 104,776	$ 144,625
Earnings per share
Basic (USD per share)	$ 0.88	$ 2.01	$ 2.84
Diluted (USD per share)	$ 0.88	$ 2	$ 2.83
Weighted average number of common shares outstanding:
Basic (shares)	53,598	53,393	53,216
Diluted (shares)	53,749	53,611	53,448
Cash Dividends Declared, per Share	$ 1.74	$ 5.93	$ 5.93

Consolidated Statements of Cash

Consolidated Statements of Cash Flows $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Operating Activities
Net income	$ 47,057	$ 107,264	$ 151,081
Adjustments to reconcile income to net cash provided by operating activities:
Depreciation and amortization, net of accretion	21,255	28,796	32,789
(Increase) decrease in cash surrender value of BOLI	(1,983)	(1,979)	(2,008)
Net realized investment (gains) losses	43,488	(16,409)	(34,875)
Share-based compensation	5,321	10,615	12,455
Deferred income tax expense (benefit)	(11,824)	1,693	8,534
Policy acquisition costs, net of amortization (net deferral)	(3,855)	(3,452)	(2,421)
Equity in (earnings) loss of unconsolidated subsidiaries	(8,948)	(8,033)	5,762
Distributed earnings from unconsolidated subsidiaries	31,219	24,392	9,863
Other	1,168	108	1,772
Other changes in assets and liabilities:
Premiums receivable	(23,381)	(14,605)	(6,446)
Reinsurance related assets and liabilities	4,697	(56,449)	(26,108)
Other assets	(4,206)	(792)	15,665
Reserve for losses and loss adjustment expenses	71,466	54,953	(11,898)
Unearned premiums	16,327	26,321	10,497
Other liabilities	(10,536)	20,965	14,321
Net cash provided (used) by operating activities	177,265	173,388	178,983
Purchases of:
Fixed maturities, available for sale	(780,698)	(614,440)	(636,377)
Fixed maturities, trading	(38,544)	0	0
Equity investments	(203,157)	(207,857)	(112,912)
Other investments	(32,153)	(50,362)	(18,613)
Funding of qualified affordable housing project tax credit partnerships	0	(507)	(1,019)
Investment in unconsolidated subsidiaries	(78,141)	(42,183)	(50,890)
Proceeds from sales or maturities of:
Fixed maturities, available for sale	914,021	932,070	752,516
Equity investments	210,481	146,356	85,226
Other investments	29,815	25,372	13,797
Return of invested capital from unconsolidated subsidiaries	84,534	32,539	7,084
Net sales or maturities (purchases) of short-term investments	123,886	4,167	(322,872)
Unsettled security transactions, net change	(4,022)	(2,031)	1,388
Purchases of capital assets	(9,636)	(10,485)	(10,922)
Repayments (advances) under Syndicate Credit Agreement	(184)	(10,339)	(1,395)
Other	(1,305)	(2,025)	6,187
Net cash provided (used) by investing activities	214,897	200,275	(288,802)
Financing Activities
Borrowings (repayments) under Revolving Credit Agreement	(123,000)	(77,000)	100,000
Proceeds (repayments) of Mortgage Loans	(1,396)	40,460	0
Repurchase of common stock	0	0	(2,106)
Dividends to shareholders	(316,476)	(315,228)	(118,812)
Capital contribution received from (return of capital to) external segregated portfolio cell participants	(1,005)	2,936	9,952
Other	(4,309)	(7,683)	(2,968)
Net cash provided (used) by financing activities	(446,186)	(356,515)	(13,934)
Increase (decrease) in cash and cash equivalents	(54,024)	17,148	(123,753)
Cash and cash equivalents at beginning of period	134,495	117,347	241,100
Cash and cash equivalents at end of period	80,471	134,495	117,347
Supplemental Disclosure of Cash Flow Information
Cash paid during the year for income taxes, net of refunds	5,726	17,193	(8,683)
Cash paid during the year for interest	16,165	15,892	14,732
Significant Non-Cash Transactions
Dividends declared and not yet paid	$ 43,446	$ 267,292	$ 265,659

Accounting Policies

Accounting Policies	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Accounting Policies	Accounting Policies Organization and Nature of Business ProAssurance Corporation (ProAssurance, PRA or the Company), a Delaware corporation, is an insurance holding company primarily for wholly owned specialty property and casualty insurance entities including an entity that is the majority capital provider to Syndicate 1729 and the sole (100%) capital provider of a SPA , Syndicate 6131 at Lloyd's. Risks insured are primarily liability risks located within the U.S. 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 16 . Principles of Consolidation The accompanying consolidated financial statements include the accounts of ProAssurance Corporation and its wholly owned subsidiaries. Investments in entities where ProAssurance holds a greater than minor interest but does not hold a controlling interest are accounted for using the equity method. All significant intercompany accounts and transactions are eliminated in consolidation. ProAssurance subsidiaries located in the U.K. are normally reported on a quarter delay due to timing issues regarding the availability of information, except when information is available that is material to the current period. Furthermore, investment results associated with ProAssurance's FAL investments and certain U.S. paid administrative expenses are reported concurrently as that information is available on an earlier time frame. Basis of Presentation The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, revenues and expenses, and disclosures related to these amounts at the date of the financial statements. Actual results could differ from those estimates. Reclassifications As a result of the third quarter of 2018 segment reorganization, prior year segment information in Note 16 has been recast to conform to the Company's current segment reporting (see Note 16 for further information). Certain other insignificant prior year amounts have been reclassified to conform to the current year presentation. Accounting Policies The significant accounting policies followed by ProAssurance in making estimates that materially affect financial reporting are summarized in these Notes to Consolidated Financial Statements. Recognition of Revenues Insurance premiums are recognized as revenues pro rata over the terms of the policies, which are principally one year in duration. Credit Losses ProAssurance's premium and agency receivables are exposed to credit losses, but to-date have not experienced any significant amount of credit losses. Recorded allowances for credit losses were less than $1.5 million at both December 31, 2018 and 2017 . Neither estimated credit losses nor actual credit write-offs, net of recoveries, exceeded $0.5 million during the years ended December 31, 2018 and 2017 . Earned But Unbilled Premiums Workers’ compensation premiums are determined based upon the payroll of the insured, the applicable premium rates and an experience-based modification factor, where applicable. An audit of the policyholders’ records is conducted after policy expiration to make a final determination of applicable premiums. Audit premium due from or due to a policyholder as a result of an audit is reflected in net premiums written and earned when billed. ProAssurance tracks, by policy, the amount of additional premium billed in final audit invoices as a percentage of payroll exposure and uses this information to estimate the probable additional amount of EBUB premium as of the balance sheet date. Changes to the EBUB estimate are included in net premiums written and earned in the period recognized. As of December 31, 2018 and 2017 , ProAssurance carried EBUB of $4.3 million as a part of premiums receivable. Losses and Loss Adjustment Expenses ProAssurance establishes its reserve for losses and LAE ("reserve for losses" or "reserve") based on estimates of the future amounts necessary to pay claims and expenses associated with the investigation and settlement of claims. The reserve for losses is determined on the basis of individual claims and payments thereon as well as actuarially determined estimates of future losses based on past loss experience, available industry data and projections as to future claims frequency, severity, inflationary trends, judicial trends, legislative changes and settlement patterns. Management establishes the reserve for losses after taking into consideration a variety of factors including premium rates, claims frequency and severity, historical paid and incurred loss development trends, the expected effect of inflation, general economic trends, the legal and political environment and the conclusions reached by internal and consulting actuaries. Management updates and reviews the data underlying the estimation of the reserve for losses each reporting period and makes adjustments to loss estimation assumptions that best reflect emerging data. Both internal and consulting actuaries perform an in-depth review of the reserve for losses on at least a semi-annual basis using the loss and exposure data of ProAssurance's subsidiaries. Consulting actuaries provide reports to management regarding the adequacy of reserves. Estimating casualty insurance reserves, and particularly long-tailed insurance reserves, is a complex process. Long-tailed insurance is characterized by the extended period of time between collecting the premium for insuring a risk and the ultimate payment of losses. For a high proportion of the risks insured or reinsured by ProAssurance, the period of time required to resolve a claim is often five years or more, and claims may be subject to litigation. Estimating losses for these long-tailed claims requires ProAssurance to make and revise judgments and assessments regarding multiple uncertainties over an extended period of time. As a result, reserve estimates may vary significantly from the eventual outcome. Reserve estimates and the assumptions on which these estimates are predicated are regularly reviewed and updated as new information becomes available. Any adjustments necessary are reflected in then current operations. Due to the size of ProAssurance’s reserve for losses, even a small percentage adjustment to these estimates could have a material effect on earnings in the period in which the adjustment is made, as was the case in 2018 , 2017 and 2016 . The effect of adjustments made to reinsured losses is mitigated by the corresponding adjustment that is made to reinsurance recoveries. Thus, in any given year, ProAssurance may make significant adjustments to gross losses that have little effect on its net losses. Reinsurance Receivables ProAssurance enters into reinsurance agreements whereby other insurance entities agree to assume a portion of the risk associated with certain policies issued by ProAssurance. In return, ProAssurance agrees to pay a premium to the reinsurer. ProAssurance uses reinsurance to provide capacity to write larger limits of liability, to provide reimbursement for losses incurred under the higher limit coverages the Company offers, to provide protection against losses in excess of policy limits, and, in the case of risk sharing arrangements, to align the Company's objectives with those of its strategic business partners and to provide custom insurance solutions for large customer groups. Receivable from reinsurers on paid losses and LAE is the estimated amount of losses already paid that will be recoverable from reinsurers. Receivable from reinsurers on unpaid losses and LAE is the estimated amount of future loss payments that will be recoverable from reinsurers. Reinsurance recoveries are the portion of losses incurred during the period that are estimated to be allocable to reinsurers. Premiums ceded are the estimated premiums that will be due to reinsurers with respect to premiums earned and losses incurred during the period. These estimates are based upon management’s estimates of ultimate losses and the portion of those losses that are allocable to reinsurers under the terms of the related reinsurance agreements. Given the uncertainty of the ultimate amounts of losses, these estimates may vary significantly from the ultimate outcome. Management regularly reviews these estimates and any adjustments necessary are reflected in the period in which the estimate is changed. Due to the size of the receivable from reinsurers, even a small adjustment to the estimates could have a material effect on ProAssurance’s results of operations for the period in which the change is made. Reinsurance contracts do not relieve ProAssurance from its obligations to policyholders. ProAssurance continually monitors its reinsurers to minimize its exposure to significant losses from reinsurer insolvencies. Any amount determined to be uncollectible is written off in the period in which the uncollectible amount is identified. 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. 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 LAE . Deferred gains are included as a component of the reserve for losses and LAE and deferred losses are included as a component of other assets on the 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. Lloyd’s Premium Estimates For certain insurance policies and reinsurance contracts written in the Lloyd’s Syndicates segment, premiums are initially recognized based upon estimates of ultimate premium. Estimated ultimate premium consists primarily of premium written under delegated underwriting authority arrangements, which consist primarily of binding authorities, and certain assumed reinsurance agreements. These estimates of ultimate premium are judgmental and are dependent upon certain assumptions, including historical premium trends for similar agreements. As reports are received from programs, ultimate premium estimates are revised, if necessary, with changes reflected in current operations. Investments Recurring Fair Value Measurements Fair values of investment securities are primarily provided by independent pricing services. The pricing services provide an exchange-traded price, if available, or provide an estimated price determined using multiple observable inputs, including exchange-traded prices for similar assets. Management reviews valuations of securities obtained from the pricing services for accuracy based upon the specifics of the security, including class, maturity, credit rating, durations, collateral and comparable markets for similar securities. Multiple observable inputs are not available for certain of the Company's investments, including corporate debt not actively traded, other asset-backed securities and investments in LP s/ LLC s. Management values the corporate debt not actively traded and the other asset-backed securities either using dealer quotes for similar securities or discounted cash flow models using yields currently available for similar securities. Management values certain investment funds, primarily LP s/ LLC s, based on the NAV of the interest held, as provided by the fund. Nonrecurring Fair Value Measurements Management measures the fair value of certain assets on a nonrecurring basis either quarterly, annually or when events or changes in circumstances indicate that the carrying amount of the assets may not be recoverable. These assets include investments carried principally at cost, investments in tax credit partnerships and equity method investments that do not provide a NAV , fixed assets, goodwill and other intangible assets. Fixed Maturities Fixed maturities are considered as either available-for-sale or trading securities. Available-for-sale securities are carried at fair value, determined as described above. Exclusive of OTTI losses, discussed in a separate section that follows, unrealized gains and losses on available-for-sale securities are included, net of related tax effects, in shareholders’ equity as a component of AOCI . Investment income includes amortization of premium and accretion of discount related to available-for-sale debt securities acquired at other than par value. Debt securities and mandatorily redeemable preferred stock with maturities beyond one year when purchased are classified as fixed maturities. Trading securities are carried at fair value, determined as described above, with the holding gains and losses included as a component of net realized investment gains (losses) during the period of change. Equity Investments Equity investments are carried at fair value, as described above, with the holding gains and losses included as a component of net realized investment gains (losses) during the period of change. Equity investments are primarily comprised of stocks, bond funds and investment funds. Short-term Investments 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. All balances are carried at fair value which approximates the cost of the securities due to their short-term nature. Other Investments Investments in convertible bond securities are carried at fair value as permitted by the accounting guidance for hybrid financial instruments, with changes in fair value recognized in income as a component of net realized investment gains (losses) during the period of change. Interest on convertible bond securities is recorded on an accrual basis based on contractual interest rates and is included in net investment income. Investments in certain funds measure fund assets at fair value on a recurring basis and provide ProAssurance with a NAV for its interest. As a practical expedient, ProAssurance considers the NAV provided to approximate the fair value of its interest. Changes in fair value are included as a component of net realized investment gains (losses) during the period of change. Investment in Unconsolidated Subsidiaries Equity investments, primarily investments in LP s/ LLC s, where ProAssurance is deemed to have influence because it holds a greater than a minor interest are accounted for using the equity method. Under the equity method, the recorded basis of the investment is adjusted each period for the investor’s pro rata share of the investee’s income or loss. Investments in unconsolidated subsidiaries include tax credit partnerships accounted for using the equity method, whereby ProAssurance’s proportionate share of income or loss is included in equity in earnings (loss) of unconsolidated subsidiaries. Tax credits received from the partnerships are recognized in the period received as a reduction to current tax expenses. Business Owned Life Insurance ProAssurance owns life insurance contracts on certain management employees. The life insurance contracts are carried at their current cash surrender value. Changes in the cash surrender value are included in income in the current period as investment income. Death proceeds from the contracts are recorded when the proceeds become payable under the policy terms. Realized Gains and Losses Realized investment gains and losses are recognized on the first-in, first-out basis for GAAP purposes and on the specific identification basis for tax purposes. Other-than-temporary Impairments ProAssurance evaluates its available-for-sale investment securities, which at December 31, 2018 and 2017 consisted entirely of fixed maturity securities, on at least a quarterly basis for the purpose of determining whether declines in fair value below recorded cost basis represent OTTI . The Company considers an OTTI to have occurred: • if there is intent to sell the security; • if it is more likely than not that the security will be required to be sold before full recovery of its amortized cost basis; or • if the entire amortized basis of the security is not expected to be recovered. The assessment of whether the amortized cost basis of a security, particularly an asset-backed debt security, is expected to be recovered requires management to make assumptions regarding various matters affecting future cash flows. The choice of assumptions is subjective and requires the use of judgment. Actual credit losses experienced in future periods may differ from management’s estimates of those credit losses. Methodologies used to estimate the present value of expected cash flows are as follows: For non-structured fixed maturities (obligations of states, municipalities and political subdivisions and corporate debt) the estimate of expected cash flows is determined by projecting a recovery value and a recovery time frame and assessing whether further principal and interest will be received. ProAssurance considers various factors in projecting recovery values and recovery time frames, including the following: • third-party research and credit rating reports; • the current credit standing of the issuer, including credit rating downgrades, whether before or after the balance sheet date; • the extent to which the decline in fair value is attributable to credit risk specifically associated with the security or its issuer; • internal assessments and the assessments of external portfolio managers regarding specific circumstances surrounding an investment, which indicate the investment is more or less likely to recover its amortized cost than other investments with a similar structure; • for asset-backed securities, the origination date of the underlying loans, the remaining average life, the probability that credit performance of the underlying loans will deteriorate in the future, and the Company's assessment of the quality of the collateral underlying the loan; • failure of the issuer of the security to make scheduled interest or principal payments; • any changes to the rating of the security by a rating agency; and • recoveries or additional declines in fair value subsequent to the balance sheet date. For structured securities (primarily asset-backed securities), ProAssurance estimates the present value of the security’s cash flows using the effective yield of the security at the date of acquisition (or the most recent implied rate used to accrete the security if the implied rate has changed as a result of a previous impairment or changes in expected cash flows). ProAssurance considers the most recently available six month averages of the levels of delinquencies, defaults, severities, and prepayments for the collateral (loans) underlying the securitization or, if historical data is not available, sector based assumptions, to estimate expected future cash flows of these securities. Exclusive of securities where there is an intent to sell or where it is not more likely than not that the security will be required to be sold before recovery of its amortized cost basis, OTTI for debt securities is separated into a credit component and a non-credit component. The credit component of an OTTI is the difference between the security’s amortized cost basis and the present value of its expected future cash flows, while the non-credit component is the remaining difference between the security’s fair value and the present value of expected future cash flows. The credit component of the OTTI is recognized in earnings while the non-credit component is recognized in OCI . Investments in tax credit partnerships are evaluated for OTTI by considering both qualitative and quantitative factors. These factors include, but are not limited to: • ProAssurance's ability and intent to hold the investment until the recovery of its carrying value; and • in situations where there was not a previous OTTI for the investment, whether the current expected cash flows from the investment, primarily tax benefits, are less than those expected at the time the investment was acquired due to various factors, such as a change in the statutory tax rate; or • in situations where there was a previous OTTI for the investment, whether the expected cash flows from the investment at the time of the OTTI, primarily tax benefits, are less than its current carrying value. Investments which are accounted for under the equity method are evaluated for impairment whenever events or changes in circumstances indicate that the carrying value of the investment may not be recoverable. These circumstances include, but are not limited to, evidence of the inability to recover the carrying value of the investment, the inability of the investee to sustain an earnings capacity that would justify the carrying value of the investment or a current fair value of the investment that is less than the carrying value. ProAssurance recognizes OTTI , exclusive of non-credit OTTI , in earnings as a part of net realized investment gains (losses). In subsequent periods, any measurement of gain, loss or impairment is based on the revised amortized basis of the security. Non-credit OTTI on debt securities and declines in fair value of available-for-sale securities not considered to be other-than-temporary are recognized in OCI . Asset-backed debt securities that have been impaired due to credit reasons or are below investment grade quality are accounted for under the effective yield method. Under the effective yield method, estimates of cash flows expected over the life of asset-backed securities are used to recognize income on the investment balance for subsequent accounting periods. Derivatives ProAssurance records derivative instruments at fair value in the Consolidated Balance Sheets. ProAssurance accounts for the changes in fair value of derivatives depending on whether the derivative is designated as a hedging instrument and if so, the type of hedging relationship. For derivative instruments not designated as hedging instruments, ProAssurance recognizes the change in fair value of the derivative in earnings during the period of change. As of December 31, 2018 , ProAssurance has not designated any derivative instruments as hedging instruments and does not use derivative instruments for trading purposes. Foreign Currency The functional currency of all ProAssurance foreign subsidiaries is the U.S. dollar. In recording foreign currency transactions, revenue and expense items are converted to U.S. dollars at the exchange rate prevailing at the transaction date. Monetary assets and liabilities originating in currencies other than the U.S. dollar are remeasured to U.S. dollars at the rates of exchange in effect as of the balance sheet date. The resulting foreign currency gains or losses are recognized in the Consolidated Statements of Income and Comprehensive Income as a component of other income. Monetary assets and liabilities include investments, cash and cash equivalents, accrued expenses and other liabilities. In addition, monetary assets and liabilities include certain premiums receivable and reserve for losses and LAE as a result of reinsurance transactions conducted with foreign cedants denominated in their local functional currencies. Cash and Cash Equivalents For purposes of the Consolidated Balance Sheets and Consolidated Statements of Cash Flows, ProAssurance considers all demand deposits and overnight investments to be cash equivalents. Deferred Policy Acquisition Costs; Ceding Commission Income Costs that vary with and are directly related to the successful production of new and renewal premiums (primarily premium taxes, commissions and underwriting salaries) are deferred to the extent they are recoverable against unearned premiums and are amortized as related premiums are earned. Unearned ceding commission income is reported as an offset to DPAC and ceding commission earned is reported as an offset to DPAC amortization. Income Taxes/Deferred Taxes ProAssurance files a consolidated federal income tax return. Tax-related interest and penalties are recognized as components of tax expense. ProAssurance evaluates tax positions taken on tax returns and recognizes positions in the financial statements when it is more likely than not that the position will be sustained upon resolution with a taxing authority. If recognized, the benefit is measured as the largest amount of benefit that has a greater than fifty percent probability of being realized. Uncertain tax positions are reviewed each period by considering changes in facts and circumstances, such as changes in tax law, interactions with taxing authorities and developments in case law, and adjustments would be made if considered necessary. Adjustments to unrecognized tax benefits may affect income tax expense and the settlement of uncertain tax positions may require the use of cash. Other than differences related to timing, no significant adjustments were considered necessary during the years ended December 31, 2018 or 2017 . Deferred federal income taxes arise from the recognition of temporary differences between the basis of assets and liabilities determined for financial reporting purposes and the basis determined for income tax purposes. ProAssurance’s temporary differences principally relate to loss reserves, unearned premium, DPAC , unrealized investment gains (losses) and basis differentials in fixed assets and investments. Deferred tax assets and liabilities are measured using the enacted tax rates expected to be in effect when such benefits are realized. ProAssurance reviews its deferred tax assets quarterly for impairment. If management determines that it is more likely than not that some or all of a deferred tax asset will not be realized, a valuation allowance is recorded to reduce the carrying value of the asset. In assessing the need for a valuation allowance, management is required to make certain judgments and assumptions about the future operations of ProAssurance based on historical experience and information as of the measurement date regarding reversal of existing temporary differences, carryback capacity, future taxable income, including its capital and operating characteristics, and tax planning strategies. A valuation allowance has been established against the full value of the deferred tax asset related to the NOL carryforwards for the U.K. operations as management concluded that it was more likely than not that the deferred tax asset will not be realized. In 2018, ProAssurance also established a valuation allowance against the deferred tax assets of certain SPC s at its newly formed wholly owned Cayman Islands reinsurance subsidiary, Inova Re. As of December 31, 2018 , these newly formed SPC s are in a cumulative pre-tax loss position, and management concluded that a valuation allowance was required based upon the weight of this negative evidence. See further discussion in Note 6 . Changes in tax laws and rates could also affect recorded deferred tax assets and liabilities in the future. On December 22, 2017, the TCJA was signed into law and contains several key provisions that impact ProAssurance, including the reduction of the corporate tax rate 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, a change in how property and casualty taxpayers discount loss reserves, a minimum tax on payments made to related foreign entities and a new tax on certain income of controlled foreign corporations. See Note 6 for further discussion of the TCJA . Real Estate Real Estate balances are reported at cost or, for properties acquired in business combinations, estimated fair value on the date of acquisition, less accumulated depreciation. Real estate principally consists of properties in use as corporate offices. Depreciation is computed over the estimated useful lives of the related property using the straight-line method. Excess office capacity is leased or made available for lease; rental income is included in other income and real estate expenses are included in operating expense. Real estate accumulated depreciation was approximately $25.2 million and $24.0 million at December 31, 2018 and 2017 , respectively. Real estate depreciation expense was $1.2 million , $1.1 million and $1.4 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. Intangible Assets Intangible assets with definite lives are amortized over the estimated useful life of the asset. Amortizable intangible assets primarily consist of policyholder relationships, renewal rights and trade names. Intangible assets with an indefinite life, primarily state licenses, are not amortized. All intangible assets are evaluated for impairment on an annual basis or upon the occurrence of certain triggering events or substantive changes in circumstances that indicate the fair value of the asset may be impaired. The third quarter 2018 segment reorganization had no impact on how ProAssurance's evaluates intangible assets for impairment. The following table provides additional information regarding ProAssurance's intangible assets. Gross Carrying Value Accumulated Amortization Amortization Expense December 31 December 31 Year Ended December 31 (In millions) 2018 2017 2018 2017 2018 2017 2016 Intangible Assets Non-amortizable $ 25.8 $ 25.8 Amortizable 97.5 97.5 $ 46.5 $ 40.3 $ 6.2 $ 5.8 $ 8.1 Total Intangible Assets $ 123.3 $ 123.3 Aggregate amortization expense for intangible assets is estimated to be $6.1 million for each of the years ended December 31, 2019 and 2020 and $6.0 million for each of the years ended December 31, 2021 , 2022 and 2023 . Goodwill Goodwill is recognized in conjunction with business acquisitions as the excess of the purchase consideration for the business acquisition over the fair value of identifiable assets acquired and liabilities assumed. The fair value of identifiable assets and liabilities, and thus goodwill, is subject to redetermination within a measurement period of up to one year following completion of a business acquisition. Management evaluates goodwill for impairment annually on October 1, upon the occurrence of certain triggering events or substantive changes in circumstances that indicate the fair value of goodwill may be impaired, and immediately before and after a reorganization that affects the composition of one or more of the Company's reporting units. Impairment of goodwill is tested at the reporting unit level, which is consistent with the reportable segments identified in Note 16 . Of the five reporting units, three have goodwill: Specialty P&C, Workers' Compensation Insurance and Segregated Portfolio Cell Reinsurance. Annual Goodwill Impairment Test When testing goodwill for impairment, management has the option to first assess qualitative factors to determine whether the existence of events or circumstances leads to a determination that it is more likely than not that the estimated fair value of a reporting unit is less than its carrying amount. If management elects to perform a qualitative assessment and determines that an impairment is more likely than not, management is then required to perform the two-step quantitative impairment test, otherwise no further analysis is required. Management also may elect not to perform the qualitative assessment and, instead, proceed directly to the two-step quantitative impairment test. As of the most recent annual evaluation date on October 1, 2018, mana

Fair Value Measurement

Fair Value Measurement	12 Months Ended
	Dec. 31, 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 December 31, 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. December 31, 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 $ — $ 120,201 $ — $ 120,201 U.S. Government-sponsored enterprise obligations — 35,354 — 35,354 State and municipal bonds — 293,772 — 293,772 Corporate debt, multiple observable inputs 2,319 1,216,834 — 1,219,153 Corporate debt, limited observable inputs — — 4,322 4,322 Residential mortgage-backed securities — 181,238 — 181,238 Agency commercial mortgage-backed securities — 13,108 — 13,108 Other commercial mortgage-backed securities — 30,993 — 30,993 Other asset-backed securities — 191,807 3,850 195,657 Fixed maturities, trading — 38,188 — 38,188 Equity investments Financial 62,344 — — 62,344 Utilities/Energy 46,533 — — 46,533 Consumer oriented 47,462 — — 47,462 Industrial 41,487 — — 41,487 Bond funds 174,753 — — 174,753 All other 50,066 — — 50,066 Short-term investments 265,910 42,409 — 308,319 Other investments — 31,341 3 31,344 Other assets — 1,884 — 1,884 Total assets categorized within the fair value hierarchy $ 690,874 $ 2,197,129 $ 8,175 2,896,178 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 20,292 Investment in unconsolidated subsidiaries 268,436 Total assets at fair value $ 3,184,906 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 years ended December 31, 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. Fixed maturities, trading , are held by the Lloyd's Syndicates segment and include U.S. Treasury obligations, U.S. Government-sponsored enterprise obligations, corporate debt with multiple observable inputs and other asset-backed securities. These securities were valued using the respective valuation methodologies discussed above for each security 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 11 , 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 December 31, 2018 , 54% 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 December 31, 2018 , 25% 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 December 31, 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) December 31, 2018 December 31, 2017 Valuation Technique Unobservable Input Range Assets: Corporate debt, limited observable inputs $4,322 $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 $3,850 $4,986 Market Comparable Comparability Adjustment 0% - 5% (2.5%) Discounted Cash Flows Comparability Adjustment 0% - 5% (2.5%) Other investments $3 $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. December 31, 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 (148 ) 2 — (146 ) Net realized investment gains (losses) (8 ) — (40 ) (48 ) Included in other comprehensive income (233 ) (105 ) — (338 ) Purchases 8,005 20,093 — 28,098 Sales (6,406 ) (438 ) (366 ) (7,210 ) Transfers in 2,627 — — 2,627 Transfers out (13,218 ) (20,688 ) — (33,906 ) Balance December 31, 2018 $ 4,322 $ 3,850 $ 3 $ 8,175 Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end $ — $ — $ — $ — December 31, 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 (163 ) — — (163 ) Net realized investment gains (losses) 13 — (143 ) (130 ) Included in other comprehensive income (369 ) (71 ) 140 (300 ) Purchases 13,016 2,627 — 15,643 Sales (4,837 ) — (912 ) (5,749 ) Transfers in 999 — 1,321 2,320 Transfers out (9,766 ) (577 ) — (10,343 ) Balance December 31, 2017 $ 13,703 $ 4,986 $ 409 $ 19,098 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 during both 2018 and 2017 were to or from Level 2. All transfers during 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 December 31, 2018 and 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 December 31, 2018 and fair values of these investments as of December 31, 2018 and 2017 was as follows: Unfunded Fair Value (In thousands) December 31, December 31, December 31, Equity investments: Mortgage fund (1)* $ — $ 20,292 $ — Investment in unconsolidated subsidiaries: Private debt funds (2) $ 20,954 18,196 42,206 Long equity fund (3) None 6,561 7,847 Long/short equity funds (4) None 28,805 31,352 Non-public equity funds (5) $ 80,076 114,811 100,062 Multi-strategy fund of funds (6) None 9,322 9,100 Credit funds (7) $ 8,916 29,164 6,561 Long/short commodities fund (8) None 12,958 13,025 Strategy focused funds (9) $ 24,539 48,619 606 268,436 210,759 Other investments: Mortgage fund (1)* See above — 20,130 Total investments carried at NAV $ 288,728 $ 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 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 December 31, 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) This 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) This 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) This 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) This 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) This 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) This investment is comprised of multiple unrelated LPs/LLCs 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 LPs, 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 December 31, 2018 , ProAssurance did not 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 ProAssurance's 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. December 31, 2018 December 31, 2017 (In thousands) Carrying Fair Carrying Fair Financial assets: BOLI $ 64,096 $ 64,096 $ 62,113 $ 62,113 Other investments $ 2,943 $ 2,943 $ 58,546 $ 69,095 Other assets $ 35,921 $ 35,468 $ 34,020 $ 33,742 Financial liabilities: Senior notes due 2023* $ 250,000 $ 264,810 $ 250,000 $ 273,153 Revolving Credit Agreement* $ — $ — $ 123,000 $ 123,000 Mortgage Loans* $ 39,064 $ 39,064 $ 40,460 $ 40,460 Other liabilities $ 21,300 $ 21,300 $ 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 $24.1 million and $20.2 million at December 31, 2018 and 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	12 Months Ended
	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Investments	Investments Available-for-sale fixed maturities at December 31, 2018 and December 31, 2017 included the following: December 31, 2018 (In thousands) Amortized Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Fixed maturities, available for sale U.S. Treasury obligations $ 121,274 $ 331 $ 1,404 $ 120,201 U.S. Government-sponsored enterprise obligations 35,758 25 429 35,354 State and municipal bonds 289,544 4,877 649 293,772 Corporate debt 1,244,577 3,328 24,430 1,223,475 Residential mortgage-backed securities 184,463 814 4,039 181,238 Agency commercial mortgage-backed securities 13,296 12 200 13,108 Other commercial mortgage-backed securities 31,330 38 375 30,993 Other asset-backed securities 196,583 254 1,180 195,657 $ 2,116,825 $ 9,679 $ 32,706 $ 2,093,798 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 December 31, 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 $ 121,274 $ 27,187 $ 74,196 $ 18,416 $ 402 $ 120,201 U.S. Government-sponsored enterprise obligations 35,758 3,279 12,301 19,640 134 35,354 State and municipal bonds 289,544 10,506 126,225 129,118 27,923 293,772 Corporate debt 1,244,577 147,223 726,570 324,467 25,215 1,223,475 Residential mortgage-backed securities 184,463 181,238 Agency commercial mortgage-backed securities 13,296 13,108 Other commercial mortgage-backed securities 31,330 30,993 Other asset-backed securities 196,583 195,657 $ 2,116,825 $ 2,093,798 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 December 31, 2018 . Cash and securities with a carrying value of $47.1 million at December 31, 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, ProAssurance is required to maintain capital at Lloyd's , referred to as FAL . ProAssurance's FAL investments at December 31, 2018 included available-for-sale fixed maturities with a fair value of $123.4 million and short-term investments with a fair value of $19.3 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 December 31, 2018 and December 31, 2017 , including the length of time the investment had been held in a continuous unrealized loss position. December 31, 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 $ 97,969 $ 1,405 $ 20,221 $ 119 $ 77,748 $ 1,286 U.S. Government-sponsored enterprise obligations 33,677 429 20,479 126 13,198 303 State and municipal bonds 63,094 648 30,924 143 32,170 505 Corporate debt 938,651 24,429 447,891 8,804 490,760 15,625 Residential mortgage-backed securities 157,120 4,039 27,311 209 129,809 3,830 Agency commercial mortgage-backed securities 9,822 200 4,566 22 5,256 178 Other commercial mortgage-backed securities 22,924 375 13,348 164 9,576 211 Other asset-backed securities 142,470 1,181 70,218 236 72,252 945 $ 1,465,727 $ 32,706 $ 634,958 $ 9,823 $ 830,769 $ 22,883 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 December 31, 2018 , excluding U.S. Government or U.S. Government-sponsored enterprise obligations, there were 1,044 debt securities ( 50.6% of all available-for-sale fixed maturity securities held) in an unrealized loss position representing 550 issuers. The greatest and second greatest unrealized loss positions among those securities were approximately $0.6 million and $0.5 million , respectively. The securities were evaluated for OTTI as of December 31, 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 . Fixed maturity securities held in an unrealized loss position at December 31, 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 December 31, 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: Year Ended December 31 (In millions) 2018 2017 2016 Proceeds from sales (exclusive of maturities and paydowns) $ 599.6 $ 530.2 $ 361.8 Purchases $ 780.7 $ 614.4 $ 636.4 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 Consolidated Balance Sheet as of December 31, 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: Year Ended December 31 (In thousands) 2018 2017 2016 Fixed maturities $ 69,515 $ 75,669 $ 85,818 Equities 21,418 17,198 14,887 Short-term investments, including Other 5,649 7,793 3,402 BOLI 1,983 1,979 2,008 Investment fees and expenses (6,681 ) (6,977 ) (6,103 ) Net investment income $ 91,884 $ 95,662 $ 100,012 Investment in Unconsolidated Subsidiaries ProAssurance's investment in unconsolidated subsidiaries were as follows: December 31, 2018 Carrying Value (In thousands) Percentage December 31, December 31, Qualified affordable housing project tax credit partnerships See below $ 65,677 $ 84,607 Other tax credit partnerships See below 3,757 6,118 All other investments, primarily investment fund LPs/LLCs See below 298,323 239,866 $ 367,757 $ 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 $25.0 million and $32.5 million at December 31, 2018 and 2017 , respectively. ProAssurance's ownership percentage relative to the remaining tax credit partnership interests is less than 20% ; these interests had a carrying value of $40.7 million and $52.1 million at December 31, 2018 and 2017 , respectively. 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 14 . 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 14 . 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 $25.9 million at December 31, 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 $272.4 million at December 31, 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: Year Ended December 31 (In thousands) 2018 2017 2016 Qualified affordable housing project tax credit partnerships Losses recorded $ 18,889 $ 14,297 $ 20,047 Tax credits recognized $ 18,474 $ 17,774 $ 18,531 Historic tax credit partnerships Losses recorded $ 5,434 $ 6,355 $ 4,771 Tax credits recognized $ 2,567 $ 5,337 $ 9,018 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): Year Ended December 31 (In thousands) 2018 2017 2016 Total OTTI losses: State and municipal bonds $ — $ (850 ) $ (100 ) Corporate debt (490 ) (419 ) (7,604 ) Investment in unconsolidated subsidiaries — (11,931 ) — Other investments — — (3,130 ) Portion of OTTI losses recognized in other comprehensive income before taxes: Corporate debt — 248 1,068 Net impairment losses recognized in earnings (490 ) (12,952 ) (9,766 ) Gross realized gains, available-for-sale fixed maturities 5,942 6,653 12,451 Gross realized (losses), available-for-sale fixed maturities (5,799 ) (3,123 ) (7,038 ) Net realized gains (losses), short-term investments (1 ) (2 ) 18 Net realized gains (losses), trading fixed maturities (100 ) — — Net realized gains (losses), equity investments 12,230 10,724 6,632 Net realized gains (losses), other investments 1,340 2,963 1,115 Change in unrealized holding gains (losses), trading fixed maturities (317 ) — — Change in unrealized holding gains (losses), equity investments (52,707 ) 11,243 30,557 Change in unrealized holding gains (losses), convertible securities, carried at fair value (3,849 ) 896 899 Other 263 7 7 Net realized investment gains (losses) $ (43,488 ) $ 16,409 $ 34,875 During 2018, ProAssurance recognized OTTI in earnings of $0.5 million related to debt instruments from two issuers in the energy sector. During 2017, ProAssurance recognized OTTI in earnings of $13.0 million , including an $8.5 million impairment related to an early stage business investment accounted for under the equity method. The impairment charge represented the difference between the investment's carrying value and fair value, which was measured as ProAssurance's ownership percentage in the projected earnings expected to be generated by the investment. In addition, ProAssurance recognized OTTI in earnings of $3.4 million related to qualified affordable housing project tax credit investments. The current estimated tax benefits expected to be received from ProAssurance's allocable portion of the operating losses of the underlying properties have declined, due to the newly enacted corporate tax rate of 21%, as compared to those at the time the investments were acquired. During 2017, ProAssurance also recognized credit-related OTTI of $0.2 million and non-credit OTTI of $0.2 million in OCI , both of which related to corporate bonds. During 2016, ProAssurance recognized OTTI in earnings of $9.8 million , including credit-related OTTI of $5.5 million related to debt instruments from ten issuers in the energy sector. The fair value of the bonds and the credit quality of the issuers had declined during 2016 and ProAssurance recognized credit-related OTTI to reduce the amortized cost basis of the bonds to the present value of future cash flows expected to be received from the bonds. During 2016, ProAssurance also recognized non-credit OTTI of $0.9 million in OCI related to certain of these same bonds, as the fair value of the bonds was less than the present value of the expected future cash flows from the securities. 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 . (In thousands) 2018 2017 2016 Balance beginning of period $ 1,313 $ 1,158 $ 5,751 Additional credit losses recognized during the period, related to securities for which: No OTTI has been previously recognized — 171 2,398 OTTI has been previously recognized — — 2,154 Reductions due to: Securities sold during the period (realized) (1,220 ) (16 ) (9,145 ) Balance December 31 $ 93 $ 1,313 $ 1,158

Retroactive Insurance Contracts

Retroactive Insurance Contracts	12 Months Ended
	Dec. 31, 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 Consolidated Statements of Income and Comprehensive Income for the year ended December 31, 2018 . In addition, ProAssurance recorded a deferred gain of $0.6 million in the reserve for losses and loss adjustment expenses in the second quarter of 2018 representing the excess of premiums received over losses assumed related to the retroactive coverage which is amortized into earnings over the estimated claim payment period. ProAssurance recognized a nominal amount of amortization related to this deferred gain during the year ended December 31, 2018 . For additional information regarding ProAssurance's accounting policy for retroactive insurance contracts, see Note 1 . Statutory Accounting and Dividend Restrictions ProAssurance’s domestic U.S. insurance subsidiaries are required to file statutory financial statements with state insurance regulatory authorities, prepared based upon SAP prescribed or permitted by regulatory authorities. ProAssurance did not use any prescribed or permitted SAP that differed from the NAIC 's SAP at December 31, 2018 , 2017 or 2016 . Differences between net income prepared in accordance with GAAP and statutory net income are principally due to: (a) policy acquisition and certain software and equipment costs which are deferred under GAAP but expensed for statutory purposes and (b) certain deferred income taxes which are recognized under GAAP but are not recognized for statutory purposes. The NAIC specifies risk-based capital requirements for property and casualty insurance providers. At December 31, 2018 , actual statutory capital and surplus for each of ProAssurance’s insurance subsidiaries substantially exceeded the regulatory requirements. Net earnings and capital and surplus of ProAssurance’s insurance subsidiaries on a statutory basis are shown in the following table. (In millions) Statutory Net Earnings Statutory Capital and Surplus 2018 2017 2016 2018 2017 $135 $139 $163 $1,041 $1,175 At December 31, 2018 , $1.3 billion of ProAssurance's consolidated net assets were held at its domestic insurance subsidiaries, of which approximately $128 million are permitted to be paid as dividends over the course of 2019 without prior approval of state insurance regulators. However, the payment of any dividend requires prior notice to the insurance regulator in the state of domicile and the regulator may prevent the dividend if, in its judgment, payment of the dividend would have an adverse effect on the capital and surplus of the insurance subsidiary.

Reinsurance

Reinsurance	12 Months Ended
	Dec. 31, 2018
Insurance [Abstract]
Reinsurance	Reinsurance ProAssurance purchases reinsurance from third-party reinsurers and insurance enterprises in order to reduce its net exposure to losses, to provide capacity to write larger limits of liability, to provide reimbursement for losses incurred under the higher limit coverages the Company offers and as a mechanism for providing custom insurance solutions. ProAssurance also uses reinsurance arrangements as a mechanism for sharing risk with insureds or their affiliates. The effects of reinsurance for the years ended December 31, 2018 , 2017 and 2016 were as follows: Year Ended December 31 (In thousands) 2018 2017 2016 Direct $ 910,198 $ 842,968 $ 794,377 Assumed 47,113 31,908 40,637 Ceded (122,397 ) (110,858 ) (96,481 ) Net premiums written $ 834,914 $ 764,018 $ 738,533 Direct $ 903,354 $ 821,249 $ 790,791 Assumed 41,535 27,629 37,805 Ceded (126,036 ) (110,347 ) (95,315 ) Net premiums earned $ 818,853 $ 738,531 $ 733,281 Losses and loss adjustment expenses $ 675,784 $ 592,218 $ 515,242 Reinsurance recoveries (82,574 ) (123,060 ) (72,013 ) Net losses and loss adjustment expenses $ 593,210 $ 469,158 $ 443,229 The receivable from reinsurers on unpaid losses and LAE represents management’s estimated amount of future loss payments that will be recoverable under ProAssurance reinsurance agreements. Most Company reinsurance agreements base the amount of premium that is due to the reinsurer in part on losses reimbursed or to be reimbursed under the agreement, and terms may also include maximum and minimum amounts of ceded premium. Ceded premium amounts are estimated based on management’s expectation of ultimate losses and the portion of those losses that are allocable to reinsurers according to the terms of the agreements, including any minimums or maximums. Given the uncertainty of the ultimate amounts of losses, management’s estimates of losses and related amounts recoverable may vary significantly from the eventual outcome. Due to changes in management’s estimates of amounts due to reinsurers related to prior accident year loss recoveries, ProAssurance increased premiums ceded by $5.5 million during the year ended December 31, 2018 and reduced premiums ceded by $1.2 million and $7.1 million during the years ended December 31, 2017 and 2016 , respectively. Reinsurance contracts do not relieve ProAssurance from its obligations to policyholders and ProAssurance remains liable to its policyholders whether or not reinsurers honor their contractual obligations. ProAssurance continually monitors its reinsurers to minimize its exposure to significant losses from reinsurer insolvencies. At December 31, 2018 , the net total amounts due from reinsurers was $340.4 million (receivables related to paid and unpaid losses and LAE and prepaid reinsurance premiums, less reinsurance premiums payable). No single reinsurer had an individual balance which exceeded $36.0 million . At December 31, 2018 reinsurance recoverables totaling approximately $77.1 million were collateralized by letters of credit or funds withheld. ProAssurance had no allowance for credit losses related to its reinsurance receivables at December 31, 2018 or 2017 as all reinsurance balances were considered collectible. During the years ended December 31, 2018 and 2016 , no reinsurance balances were written off for credit reasons. During the year ended December 31, 2017 , reinsurance balances written off for credit reasons were nominal in amount. During 2018 , 2017 and 2016, ProAssurance commuted the 2016, 2015 and 2014 calendar year quota share reinsurance arrangements, respectively, between the Specialty P&C segment and Syndicate 1729 which resulted in a net cash receipt of approximately $6.1 million , $6.3 million and $6.8 million , respectively. The commutation s reduced the receivable from reinsurers on unpaid losses and LAE, combined, by approximately $6.7 million , $6.6 million and $7.1 million during the years ended December 31, 2018 , 2017 and 2016, respectively. During 2017, ProAssurance commuted an outstanding DDR reinsurance arrangement with one of its reinsurers which resulted in a net cash receipt of approximately $7.8 million and reduced its receivable from reinsurers on unpaid losses and LAE by approximately $5.4 million . During 2016, ProAssurance entered into a novation agreement which represents a legal replacement of one insurer by another extinguishing the ceding entity's liability to the policyholder. The novation resulted in approximately $11.8 million of one-time assumed premium which was fully earned at the inception of the agreement as all of the underlying loss events covered by the policy occurred in the past.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes Deferred income taxes reflect the net tax effects of temporary differences between the amount of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Significant components of ProAssurance’s deferred tax assets and liabilities were as follows: December 31 (In thousands) 2018 2017 Deferred tax assets Unpaid loss discount $ 30,629 $ 20,368 Unearned premium adjustment 16,620 14,449 Compensation related 9,879 11,467 Unrealized losses on investments, net 4,403 — Basis differentials–investments 912 — Intangibles 433 514 Foreign NOL 6,795 4,116 Total gross deferred tax assets 69,671 50,914 Valuation allowance (7,074 ) (4,116 ) Total deferred tax assets, net of valuation allowance 62,597 46,798 Deferred tax liabilities Deferred policy acquisition costs (9,972 ) (6,333 ) Unpaid loss discount–transition (10,128 ) — Unrealized gains on investments, net — (5,166 ) Fixed assets (542 ) (826 ) Basis differentials–investments — (10,397 ) Intangibles (11,243 ) (12,548 ) Other (1,604 ) (1,598 ) Total deferred tax liabilities (33,489 ) (36,868 ) Net deferred tax assets (liabilities) $ 29,108 $ 9,930 ProAssurance had $34.0 million of available NOL carryforwards at December 31, 2018 related to the Company's U.K. operations which may be carried forward indefinitely. At December 31, 2018 and 2017 , ProAssurance established a deferred tax asset related to the NOL carryforwards of $6.8 million and $4.1 million , respectively. In 2018 and 2017, management evaluated the realizability of the deferred tax asset related to the U.K. NOL carryforwards and concluded that it was more likely than not that the deferred tax asset will not be realized; therefore, a valuation allowance was recorded against the full value of the deferred tax asset related to the U.K. NOL carryforwards in both 2018 and 2017. The increase in the deferred tax asset related to the U.K. NOL carryforwards and the related valuation allowance in 2018 as compared to 2017 of $2.7 million was primarily due to natural catastrophe-related losses recognized in the Lloyd's Syndicates segment during 2018 related to Hurricanes Michael and Florence as well as volcanic eruptions in Hawaii. During 2018, the Company restructured its Cayman Islands operations which resulted in the formation of a new subsidiary, Inova Re. Our deferred tax assets and liabilities include those of the SPCs at Inova Re, net of a valuation allowance of $0.3 million at December 31, 2018 . Due to the limited operations of these newly formed SPCs as of December 31, 2018 , management concluded that a valuation allowance was required. ProAssurance had no available capital loss carryforwards or Alternative Minimum Tax credit carryforwards as of December 31, 2018 . ProAssurance files income tax returns in various states, the U.S. federal jurisdiction and the U.K. ProAssurance had a receivable for U.S. federal and U.K. income taxes of $3.5 million at December 31, 2018 , carried as a part of other assets. At December 31, 2017 , ProAssurance had a liability for U.S. federal and U.K. income taxes of $8.0 million , carried as a part other liabilities. The statute of limitations is now closed for all tax years prior to 2015 . A reconciliation of the beginning and ending amounts of unrecognized tax benefits for 2018 , 2017 and 2016 , were as follows: (In thousands) 2018 2017 2016 Balance at January 1 $ 5,341 $ 8,353 $ 8,195 Increases for tax positions taken during the current year — — 361 (Decreases) for tax positions taken during the current year (777 ) (3,500 ) — (Decreases)/increases for tax positions taken during prior years (800 ) 700 — (Decreases) relating to a lapse of the applicable statute of limitations (163 ) (212 ) (203 ) Balance at December 31 $ 3,601 $ 5,341 $ 8,353 At December 31, 2018 and 2017 , approximately $1.2 million and $1.3 million , respectively, of ProAssurance's uncertain tax positions, if recognized, would affect the effective tax rate. As with any uncertain tax position, there is a possibility that the ultimate benefit realized could differ from the estimate management has established. Management believes that it is reasonably possible that a portion of unrecognized tax benefits at December 31, 2018 may change during the next twelve months. However, an estimate of the change cannot be made at this time. ProAssurance recognizes interest and/or penalties related to income tax matters in income tax expense. Interest recognized in the income statement was nominal for the year ended December 31, 2018 and was approximately $0.3 million and $0.2 million for the years ended December 31, 2017 and 2016 , respectively. The accrued liability for interest was approximately $0.6 million at December 31, 2018 and $0.5 million at December 31, 2017 . Income tax expense (benefit) for each of the years ended December 31, 2018 , 2017 and 2016 consisted of the following: (In thousands) 2018 2017 2016 Provision for income taxes Current expense (benefit) Federal and foreign $ (6,509 ) $ 19,546 $ 15,857 State 301 120 729 Total current expense (benefit) (6,208 ) 19,666 16,586 Deferred expense (benefit) Federal and foreign (11,765 ) 1,331 8,284 State (59 ) 362 250 Total deferred expense (benefit) (11,824 ) 1,693 8,534 Total income tax expense (benefit) $ (18,032 ) $ 21,359 $ 25,120 A reconciliation of “expected” income tax expense (benefit) (21% of income before income taxes for 2018; 35% of income before income taxes for 2017 and 2016) to actual income tax expense (benefit) for each of the years ended December 31, 2018 , 2017 and 2016 were as follows: (In thousands) 2018 2017 2016 Computed “expected” tax expense $ 6,095 $ 45,018 $ 61,670 Tax-exempt income (2,505 ) (8,356 ) (9,917 ) Tax credits (21,059 ) (23,111 ) (27,549 ) Non-U.S. operating results 2,269 918 (1,688 ) Excess tax benefit on share-based compensation (275 ) (2,762 ) — Change in federal corporate tax rate — 6,541 — Change in limitation of future deductibility of certain executive compensation — 3,497 — Provision-to-return differences (2,309 ) (1,979 ) 1,209 Other (248 ) 1,593 1,395 Total income tax expense (benefit) $ (18,032 ) $ 21,359 $ 25,120 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 change in how property and casualty taxpayers discount loss reserves, a minimum tax on payments made to related foreign entities and a new tax on certain income of controlled foreign corporations. 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 16 . 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 year ended December 31, 2018 . The TCJA also requires a U.S. shareholder of a controlled foreign corporation to include its GILTI in U.S. taxable income. The GILTI amount is based on the U.S. shareholder’s aggregate share of the gross income of the controlled foreign corporation reduced by certain exceptions and a net deemed tangible income return. The net deemed tangible income return is based on the controlled foreign corporation’s basis in the tangible depreciable business property. Cell rental fee income earned by Inova Re and Eastern Re fall within the scope of the GILTI provisions of the TCJA . Management has evaluated the new GILTI provisions of the TCJA and has made an accounting policy election to treat the taxes due on inclusions of GILTI in U.S. taxable income as a current period expense when incurred. Under current accounting guidance, the effects of changes in tax rates and laws are recognized in the period in which the new legislation is enacted. However, due to the timing of the enactment of the TCJA and its proximity to December 31, 2017, the SEC issued SAB 118 which provided a framework for companies to account for uncertainties in applying the provisions of the TCJA . SAB 118 allowed companies to record a provisional amount in situations where a company did not have the necessary information available but could make a reasonable estimate. In situations where companies could not make a reasonable estimate due to various factors, including lack of information, a provisional amount was not recorded. Instead, companies continued to apply current accounting guidance based on the provision of the tax laws that were in effect immediately prior to the TCJA being enacted. The measurement period, as defined in SAB 118 for the TCJA , began on the enactment date of the TCJA and ended when a company obtained, prepared and analyzed the information that was needed in order to complete the accounting requirements under current accounting guidance. However, under no circumstances would the measurement period extend beyond one year from the enactment date of the TCJA . Other than the areas discussed below, ProAssurance was able to complete its accounting for all areas of the TCJA during the period of enactment and recognized a charge of $6.5 million , which was included as a component of income tax expense from continuing operations for the year ended December 31, 2017. Provisional amount finalized during the third quarter of 2018 The TCJA placed limitations on the future deductibility of certain executive compensation. At December 31, 2017, the IRS had not yet issued guidance in this area, and thus ProAssurance made a reasonable estimate of the effects on its existing deferred tax balances related to executive compensation at that time and recorded a provisional charge of $3.5 million 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 its December 31, 2017 deferred tax balances related to executive compensation. As a result, ProAssurance did not record any measurement-period adjustments to the previously recorded provisional amount. Provisional amounts finalized during the fourth quarter of 2018 In computing taxable income, property and casualty insurance companies reduce their premiums earned by losses incurred. The tax deduction for losses incurred is discounted using interest rates and factors prescribed by the IRS . The TCJA modified the rules for discounting losses incurred by changing the definition of the applicable interest rate that is used and amending the time periods for the loss payment pattern. These new provisions are effective for tax years beginning after December 31, 2017 and are subject to a transition rule. At December 31, 2017, the IRS had not yet released the information necessary for the Company to determine a reasonable estimate for the tax effects of the TCJA on its deferred tax balances related to loss reserve discounting; therefore, no provisional amount was recorded at that time. During the fourth quarter of 2018, ProAssurance was able to complete its analysis during the measurement period following the release of new discount factors by the IRS on December 19, 2018. ProAssurance used the new discount factors to determine the impact of the TCJA on its deferred tax balances related to loss reserve discounting. The adjustment, which is referred to as the transition rule adjustment, will be reflected as a component of taxable income evenly over eight years beginning in 2018. This transition rule adjustment is a taxable temporary difference and has no impact on total tax expense for the current year. The ultimate impact of the TCJA on the Company's deferred tax balances for loss reserve discounting could differ, perhaps materially, if the IRS publishes any future revisions to the loss discount factors used in its analysis.

Deferred Policy Acquisition Cos

Deferred Policy Acquisition Costs	12 Months Ended
	Dec. 31, 2018
Insurance [Abstract]
Deferred Policy Acquisition Costs	Deferred Policy Acquisition Costs Policy acquisition costs that are incremental and directly related to the successful production of new and renewal insurance contracts, most significantly agent commissions, premium taxes, and underwriting salaries and benefits, are capitalized as policy acquisition costs and amortized to expense, net of ceding commissions earned, as the related premium revenues are earned. Amortization of DPAC was $104.5 million , $95.8 million and $88.4 million for the years ended December 31, 2018 , 2017 and 2016 , respectively.

Reserve for Losses and Loss Adj

Reserve for Losses and Loss Adjustment Expenses	12 Months Ended
	Dec. 31, 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. For a high proportion of the risks insured or reinsured by ProAssurance, 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. IBNR reserves are not estimated directly, but are calculated by subtracting claim payments to-date and case reserves as of the evaluation date from the projected ultimate losses which are determined as described below. 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 over 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. Reserving Methodologies For the HCPL, medical technology and workers’ compensation lines of business, the analysis performed by the consulting actuaries analyzes each partition of the business in a variety of ways and uses multiple actuarial methodologies in performing these analyses, including: Bornhuetter-Ferguson (Paid and Reported) Method, Paid Development Method, Reported Development Method, Average Paid Value Method, Average Reported Value Method, Backward Recursive Development Method, the Adjusted Reported and the Adjusted Paid Methods. Generally, methods such as the Bornhuetter-Ferguson method are used on more recent accident years where there is less data available on which to base the analysis. As time progresses and an increased amount of data is available for a given accident year, management gives more confidence to the development and average methods, as these methods typically rely more heavily on ProAssurance's own historical data. These methods emphasize different aspects of loss reserve estimation and provide a variety of perspectives for ProAssurance's decisions. For the workers’ compensation line of business in both the Workers' Compensation Insurance and Segregated Portfolio Cell Reinsurance segments, ProAssurance utilizes the Reported Development Method, Paid Loss Development Method and Bornhuetter-Ferguson, to develop the reserve for each accident year. The actuarial review includes the stratification of claims data (lost time claims and medical only claims) using different variations that allow for identification of trends that may not be readily identifiable if the data was evaluated only in the aggregate. Reported and paid loss development factors are key assumptions in the reserve estimation process and are based on ProAssurance’s historical reported and paid loss development patterns. As accident years mature, the various actuarial methodologies produce more consistent loss estimates. For the Lloyd’s Syndicates segment business, given the immaturity of Syndicate 1729 and Syndicate 6131’s own experience, losses are initially estimated using the loss assumptions by risk category incorporated into the business plan submitted to Lloyd’s with consideration given to loss experience incurred to date. These assumptions were influenced by loss results reflected in Lloyd’s historical data for similar risks. As losses are reported and resolved and loss experience becomes more credible from a statistical perspective, actual loss experience is incorporated into the estimates. Certain of the methodologies utilized to estimate the ultimate losses for each partition of the reserve consider the actual amounts paid. Paid data is particularly influential when a large portion of known claims have been closed, as is the case for older accident years. In selecting a point estimate for each partition, management considers the extent to which trends are emerging consistently for all partitions and known industry trends. Thus, actual, rather than estimated severity trends are given more consideration. If actual severity trends are lower than those estimated at the time that reserves were previously established, the recognition of favorable development is indicated. This is particularly true for older accident years where actuarial methodologies give more weight to actual loss costs (severity). The various actuarial methods discussed above are applied in a consistent manner from period to period. In addition, ProAssurance performs statistical reviews of claims data such as claim counts, average settlement costs and severity trends when establishing the reserve. Selected point estimates of ultimate losses are utilized to develop estimates of ultimate losses recoverable from reinsurers, based on the terms and conditions of ProAssurance’s reinsurance agreements. An overall estimate of the amount receivable from reinsurers is determined by combining the individual estimates. ProAssurance’s net reserve estimate is the gross reserve point estimate less the estimated reinsurance recovery. Activity in the reserve for losses and loss adjustment expenses is summarized as follows: (In thousands) 2018 2017 2016 Balance, beginning of year $ 2,048,381 $ 1,993,428 $ 2,005,326 Less reinsurance recoverables on unpaid losses and loss adjustment expenses 335,585 273,475 249,350 Net balance, beginning of year 1,712,796 1,719,953 1,755,976 Net losses: Current year* 685,326 603,518 587,007 Favorable development of reserves established in prior years, net (92,116 ) (134,360 ) (143,778 ) Total 593,210 469,158 443,229 Paid related to: Current year (117,268 ) (106,633 ) (96,190 ) Prior years (412,711 ) (369,682 ) (383,062 ) Total paid (529,979 ) (476,315 ) (479,252 ) Net balance, end of year 1,776,027 1,712,796 1,719,953 Plus reinsurance recoverables on unpaid losses and loss adjustment expenses 343,820 335,585 273,475 Balance, end of year $ 2,119,847 $ 2,048,381 $ 1,993,428 * Current year net losses in 2018 included incurred losses of $25.4 million related to a loss portfolio transfer entered into during the second quarter of 2018 (see Note 4). As discussed in Note 1 , estimating liability reserves is complex and requires the use of many assumptions. As time passes and ultimate losses for prior years are either known or become subject to a more precise estimation, ProAssurance increases or decreases the reserve estimates established in prior periods. The favorable loss development recognized in 2018 primarily reflected a lower than anticipated claims severity trend (i.e. the average size of a claim) for accident years 2011 through 2014 . The favorable development recognized in 2017 and 2016 was primarily due to lower than anticipated claims severity trends for accident years 2010 through 2014 and accident years 2009 through 2013 , respectively. On January 1, 2016, ProAssurance adopted new guidance that requires detailed disclosures related to its reserve for losses and loss adjustment expenses, including significant changes in methodologies and assumptions used in the calculation of its reserve. ProAssurance establishes its reserve and manages claims activity by coverage, product or line of business and various categories of reserves have similar characteristics. Therefore, ProAssurance has aggregated these reserve categories into several reserve groups that provide a more meaningful view of the amount, timing and uncertainty of cash flows arising from the liability. At the same time, these reserve groups present a disaggregated view of the major elements of the overall loss reserve liability. The reserve groups include HCPL claims-made reserve, HCPL occurrence reserve, medical technology liability claims-made reserve, workers’ compensation insurance reserve, segregated portfolio cell reinsurance - workers' compensation reserve, Syndicate 1729 casualty reserve, Syndicate 1729 property insurance reserve and Syndicate 1729 property reinsurance reserve. All other loss reserve categories are deemed to be less homogeneous or relatively small on a standalone basis and are included in other short-duration lines in the claims development reconciliation. The composition of the reserve groups is based on similar characteristics with respect to the risks being insured and the reporting and payout pattern of the underlying claims. In most instances the groups follow the coverage categorizations used in statutory financial reporting for U.S.-domiciled property-casualty insurance companies. HCPL claims are disaggregated into those claims covered by claims-made policies and those claims covered by occurrence policies. For claims-made policies, the insured event generally becomes a liability when the event is first reported to the insurer. For occurrence policies, the insured event becomes a liability when the event takes place, even if unknown at that time. Claims-made coverage has a short reporting pattern, with virtually all claims known shortly after the end of the policy period. Occurrence coverage claims can have an extended reporting pattern, with the time from the loss event until the filing of the claim often measured in years, at which point the claims resolution process begins. Although the resolution process and time frame is similar once a claim is reported, combining claims from claims-made and occurrence coverage types would result in distortion due to the difference in reporting lag. Medical technology liability reserves are grouped separately due to the nature of the risk, including the potential for mass torts and multiple claims arising out of the same product or service. The small amount of medical technology liability occurrence reserves are included in other short-duration lines. Workers' compensation reserves in the Workers' Compensation Insurance and the Segregated Portfolio Cell Reinsurance segment are each grouped separately due to the difference in the type of coverage provided and the differences in the claims resolution process as compared to other liability insurance. The small amount of HCPL reserves in the Segregated Portfolio Cell Reinsurance segment are included in other short-duration lines. Finally, claims arising from the Company's involvement in Syndicate 1729 are segregated into casualty (insurance and reinsurance), property insurance and property reinsurance groups. Property insurance claims generally have a shorter reporting and resolution time frame as compared to most casualty claims. The reporting and resolution patterns of property reinsurance claims differs from that of property insurance claims due to predominant coverage of catastrophic loss events on an aggregate basis rather than coverage of individual claims. Casualty reinsurance, on the other hand, generally provides coverage on a per-claim basis and the reporting and resolution time frame for these claims is not substantially different than those arising from casualty insurance written by Syndicate 1729. The small amount of reserves associated with Syndicate 6131 related to contingency and special property business are included in other short-duration lines. ProAssurance has elected to present reserve history for acquired entities in all periods shown in the tables below, including periods prior to acquisition. With the exception of the workers' compensation insurance and segregated portfolio cell workers' compensation reinsurance lines of business, virtually all other acquired entities are captured within the HCPL line of business. All information prior to 2018 disclosed in the Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance, Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance and Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance tables that follow is presented as supplementary information. The “Cumulative Number of Reported Claims” in the tables that follow includes the combined number of claims for an accident year and excludes projected unreported IBNR claims. A claim is considered reported when ProAssurance becomes aware of and accepts it for coverage under the terms of the Company's insurance contracts. Healthcare Professional Liability Reserve HCPL loss costs are impacted by many factors, including but not limited to the nature of the claim, including whether or not the claim is an individual or a mass tort claim, the personal situation of the claimant or the claimant's family, the outcome of jury trials, the legislative and judicial climate where any potential litigation may occur, general economic conditions and, for claims involving bodily injury, the trend of healthcare costs. ProAssurance sets an initial reserve using the average loss ratio used in pricing, plus an additional provision in consideration of the historical loss volatility ProAssurance and others in the industry have experienced. The average initial loss ratio for HCPL business has approximated 90% for recent years, which is higher than the underlying expected loss ratio due to provisions for loss volatility. Changes in observed claim frequency, severity or a combination of the two can result in variations in loss provisions. The reasons for the variability in loss provisions from period to period have included additional loss activity within ProAssurance’s excess and surplus lines business, provisions for losses in excess of policy limits, adjustments to ULAE, adjustments to the reserve for the DDR provisions in ProAssurance's policies and additional losses recorded for particular exposures, such as mass torts. These specific adjustments are made if ProAssurance believes the results for a given accident year are likely to exceed those anticipated by pricing. ProAssurance believes the use of a provision for volatility appropriately considers the inherent risks and limitations of the rate development process and the historic volatility of professional liability losses and produces a reasonable best estimate of the reserve required to cover actual ultimate unpaid losses. Healthcare Professional Liability Claims-Made Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2018 ($ in thousands) Year Ended December 31, IBNR* Cumulative Number of Reported Claims 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 Accident Year Unaudited 2009 $ 379,259 $ 370,642 $ 345,714 $ 320,368 $ 284,511 $ 265,478 $ 246,146 $ 230,849 $ 224,768 $ 220,703 $ (455 ) 3,828 2010 — $ 364,996 $ 354,787 $ 338,170 $ 312,813 $ 291,553 $ 279,713 $ 270,484 $ 258,466 257,714 $ (243 ) 3,847 2011 — — $ 348,916 $ 344,808 $ 331,884 $ 305,540 $ 289,400 $ 278,258 $ 264,777 254,329 $ (2,091 ) 3,532 2012 — — — $ 341,289 $ 324,418 $ 319,613 $ 306,956 $ 291,075 $ 279,589 271,110 $ 276 3,702 2013 — — — — $ 315,346 $ 304,209 $ 296,550 $ 287,140 $ 272,364 258,251 $ 173 3,783 2014 — — — — — $ 290,020 $ 289,397 $ 280,043 $ 267,442 256,968 $ (5,200 ) 3,320 2015 — — — — — — $ 276,492 $ 269,980 $ 271,138 270,814 $ (8,030 ) 3,266 2016 — — — — — — — $ 271,765 $ 274,643 287,551 $ (21,456 ) 3,481 2017 — — — — — — — — $ 283,746 295,883 $ (11,228 ) 3,677 2018 — — — — — — — — — 320,772 $ 129,334 3,558 Total $ 2,694,095 * Includes expected development on reported claims Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (In thousands) Year Ended December 31, 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 Accident Year Unaudited 2009 $ 15,051 $ 71,272 $ 114,318 $ 153,563 $ 178,445 $ 191,420 $ 200,425 $ 205,372 $ 209,016 $ 213,568 2010 — $ 15,464 $ 69,551 $ 137,712 $ 180,432 $ 209,777 $ 221,693 $ 236,171 $ 240,945 243,675 2011 — — $ 14,417 $ 71,208 $ 133,004 $ 177,089 $ 198,112 $ 214,502 $ 224,982 233,103 2012 — — — $ 15,382 $ 73,571 $ 145,488 $ 190,997 $ 215,220 $ 231,652 244,512 2013 — — — — $ 16,938 $ 69,657 $ 127,496 $ 171,681 $ 197,265 213,879 2014 — — — — — $ 16,764 $ 59,485 $ 116,791 $ 154,236 186,239 2015 — — — — — — $ 9,172 $ 55,731 $ 111,741 161,896 2016 — — — — — — — $ 9,027 $ 51,869 109,756 2017 — — — — — — — — $ 16,309 63,171 2018 — — — — — — — — — 14,051 Total 1,683,850 All outstanding liabilities before 2009, net of reinsurance 11,724 Liabilities for losses and loss adjustment expenses, net of reinsurance $ 1,021,969 Healthcare Professional Liability Occurrence Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2018 ($ in thousands) Year Ended December 31, IBNR* Cumulative Number of Reported Claims 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 Accident Year Unaudited 2009 $ 34,450 $ 35,366 $ 36,802 $ 37,437 $ 34,099 $ 32,675 $ 28,731 $ 26,340 $ 24,572 $ 23,387 $ 1,519 246 2010 — $ 41,721 $ 43,238 $ 43,195 $ 42,233 $ 37,920 $ 35,831 $ 33,361 $ 29,338 26,501 $ 946 290 2011 — — $ 45,882 $ 44,956 $ 41,453 $ 39,917 $ 37,150 $ 35,004 $ 32,343 29,784 $ 2,136 342 2012 — — — $ 45,703 $ 46,513 $ 44,848 $ 40,692 $ 34,774 $ 32,691 29,857 $ 3,816 399 2013 — — — — $ 32,746 $ 36,602 $ 35,624 $ 34,393 $ 30,906 26,919 $ 971 356 2014 — — — — — $ 30,420 $ 29,918 $ 32,143 $ 29,869 25,885 $ 2,778 355 2015 — — — — — — $ 35,648 $ 35,347 $ 37,346 40,960 $ 4,667 355 2016 — — — — — — — $ 29,609 $ 28,790 27,240 $ 6,244 322 2017 — — — — — — — — $ 24,571 23,760 $ 19,890 270 2018 — — — — — — — — — 38,420 $ 36,196 118 Total $ 292,713 * Includes expected development on reported claims Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (In thousands) Year Ended December 31, 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 Accident Year Unaudited 2009 $ 175 $ 2,255 $ 5,067 $ 7,947 $ 10,823 $ 13,248 $ 15,380 $ 16,025 $ 16,270 $ 17,022 2010 — $ 285 $ 1,881 $ 5,647 $ 9,120 $ 15,147 $ 21,837 $ 22,804 $ 23,313 23,832 2011 — — $ 291 $ 2,803 $ 8,059 $ 16,544 $ 19,197 $ 21,416 $ 23,194 24,539 2012 — — — $ 363 $ 2,430 $ 7,705 $ 12,212 $ 19,275 $ 21,435 23,095 2013 — — — — $ 369 $ 3,170 $ 7,826 $ 14,753 $ 16,787 18,949 2014 — — — — — $ 394 $ 2,260 $ 7,460 $ 10,519 14,604 2015 — — — — — — $ (350 ) $ 786 $ 4,854 11,626 2016 — — — — — — — $ (182 ) $ (195 ) 2,883 2017 — — — — — — — — $ (6,809 ) (5,858 ) 2018 — — — — — — — — — 65 Total 130,757 All outstanding liabilities before 2009, net of reinsurance 7,985 Liabilities for losses and loss adjustment expenses, net of reinsurance $ 169,941 Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance Years 1 2 3 4 5 6 7 8 9 10 Unaudited Healthcare Professional Liability Claims-Made 5.4% 19.5% 22.8% 17.0% 10.4% 5.9% 4.6% 2.4% 1.4% 2.1% Healthcare Professional Liability Occurrence (2.3%) 6.1% 15.0% 17.6% 15.2% 11.7% 6.1% 3.1% 1.5% 3.2% Medical Technology Liability Reserve The risks insured in the medical technology liability line of business are more varied and policies are individually priced based on the risk characteristics of the policy and the account. These policies often have substantial deductibles or self-insured retentions and the insured risks range from startup operations to large multinational entities. Premiums are established using the most recently developed actuarial estimates of losses expected to be incurred based on factors which include: results from prior analysis of similar business, industry indications, observed trends and judgment. Claims in this line of business primarily involve bodily injury to individuals and are affected by factors similar to those of the HCPL line of business. For the medical technology liability line of business, ProAssurance also establishes an initial reserve using a loss ratio approach, including a provision in consideration of historical loss volatility that this line of business has exhibited. Medical Technology Liability Claims-Made Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2018 ($ in thousands) Year Ended December 31, IBNR* Cumulative Number of Reported Claims 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 Accident Year Unaudited 2009 $ 30,462 $ 31,183 $ 27,523 $ 26,181 $ 23,425 $ 21,733 $ 20,551 $ 19,264 $ 18,176 $ 17,984 $ 251 699 2010 — $ 26,077 $ 27,063 $ 25,175 $ 23,307 $ 19,315 $ 17,439 $ 16,047 $ 16,878 18,611 $ 402 498 2011 — — $ 17,249 $ 20,930 $ 19,166 $ 15,836 $ 13,794 $ 12,487 $ 12,358 8,202 $ 500 521 2012 — — — $ 11,162 $ 9,989 $ 8,906 $ 7,441 $ 5,824 $ 4,797 5,051 $ 732 220 2013 — — — — $ 9,807 $ 9,955 $ 9,536 $ 7,226 $ 4,697 3,566 $ 380 218 2014 — — — — — $ 9,989 $ 10,306 $ 9,012 $ 8,984 7,679 $ 2,544 272 2015 — — — — — — $ 9,376 $ 8,757 $ 7,193 5,929 $ 2,770 155 2016 — — — — — — — $ 9,200 $ 8,467 7,413 $ 3,482 180 2017 — — — — — — — — $ 11,049 10,143 $ 7,834 95 2018 — — — — — — — — — 10,141 $ 9,818 188 Total $ 94,719 * Includes expected development on reported claims Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (In thousands) Year Ended December 31, 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 Accident Year Unaudited 2009 $ 116 $ 5,071 $ 7,742 $ 14,675 $ 14,933 $ 15,097 $ 15,184 $ 15,186 $ 16,515 $ 17,522 2010 — $ 485 $ 3,557 $ 8,491 $ 12,283 $ 11,725 $ 12,146 $ 12,253 $ 15,366 17,660 2011 — — $ 118 $ 2,034 $ 3,846 $ 5,062 $ 7,376 $ 7,240 $ 7,799 7,664 2012 — — — $ 568 $ 1,520 $ 2,805 $ 3,247 $ 3,366 $ 3,676 3,800 2013 — — — — $ 102 $ 1,029 $ 1,967 $ 2,599 $ 3,092 3,102 2014 — — — — — $ 388 $ 1,527 $ 2,564 $ 3,046 3,724 2015 — — — — — — $ 25 $ 440 $ 1,625 2,097 2016 — — — — — — — $ 53 $ 1,690 2,365 2017 — — — — — — — — $ 56 1,681 2018 — — — — — — — — — 6 Total 59,621 All outstanding liabilities before 2009, net of reinsurance 1,101 Liabilities for losses and loss adjustment expenses, net of reinsurance $ 36,199 Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance Years 1 2 3 4 5 6 7 8 9 10 Unaudited Medical Technology Liability 2.6 % 19.1 % 19.7 % 16.4 % 8.6 % 1.6 % 2.6 % 5.0 % 9.9 % 5.6 % Workers' Compensation Insurance Reserve Many factors affect the ultimate losses incurred for the workers' compensation coverages in the Workers' Compensation Insurance segment including, but not limited to, the type and severity of the injury, the age and occupation of the injured worker, the estimated length of disability, medical treatment and related costs, and the jurisdiction and workers' compensation laws of the injury occurrence. ProAssurance uses various actuarial methodologies in developing the workers’ compensation reserve combined with a review of the exposure base generally based upon payroll of the insured. For the current accident year, given the lack of seasoned information, the different actuarial methodologies produce results with considerable variability; therefore, more emphasis is placed on supplementing results from the actuarial methodologies with trends in exposure base, medical expense inflation, general inflation, severity, and claim counts, among other things, to select an expected loss ratio. Workers' Compensation Insurance Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2018 ($ in thousands) Year Ended December 31, IBNR* Cumulative Number of Reported Claims 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 Accident Year Unaudited 2009 $ 45,354 $ 45,354 $ 45,354 $ 45,354 $ 47,811 $ 48,372 $ 47,905 $ 47,480 $ 47,480 $ 47,480 $ 80 10,129 2010 — $ 55,852 $ 55,852 $ 55,852 $ 54,837 $ 54,779 $ 55,200 $ 54,600 $ 54,600 54,600 $ 58 12,913 2011 — — $ 65,665 $ 65,783 $ 71,521 $ 72,280 $ 72,420 $ 72,495 $ 72,795 72,795 $ 354 15,244 2012 — — — $ 80,285 $ 76,551 $ 75,848 $ 76,357 $ 75,836 $ 75,636 75,136 $ 724 16,204 2013 — — — — $ 86,973 $ 85,935 $ 86,928 $ 88,010 $ 88,810 88,810 $ 1,017 16,429 2014 — — — — — $ 93,019 $ 93,529 $ 93,029 $ 92,229 92,229 $ 3,350 16,210 2015 — — — — — — $ 100,101 $ 100,454 $ 98,454 97,654 $ 8,522 16,548 2016 — — — — — — — $ 101,348 $ 97,348 92,148 $ 13,540 15,972 2017 — — — — — — — — $ 99,874 99,874 $ 12,489 16,058 2018 — — — — — — — — — 118,095 $ 32,816 17,556 Total $ 838,821 * Includes expected development on reported claims Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (In thousands) Year Ended December 31, 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 Accident Year Unaudited 2009 $ 14,701 $ 31,465 $ 39,351 $ 43,436 $ 45,689 $ 46,321 $ 46,928 $ 47,012 $ 47,089 $ 47,189 2010 — $ 20,086 $ 39,098 $ 46,762 $ 51,117 $ 52,530 $ 53,443 $ 53,734 $ 53,974 54,014 2011 — — $ 21,993 $ 50,900 $ 62,307 $ 67,945 $ 70,146 $ 70,934 $ 71,662 71,856 2012 — — — $ 27,448 $ 56,122 $ 65,908 $ 70,558 $ 72,766 $ 73,662 73,676 2013 — — — — $ 30,554 $ 63,825 $ 76,813 $ 82,369 $ 85,689 86,783 2014 — — — — — $ 30,368 $ 65,922 $ 77,631 $ 85,022 87,314 2015 — — — — — — $ 32,078 $ 65,070 $ 78,947 83,483 2016 — — — — — — — $ 28,377 $ 58,192 69,237 2017 — — — — — — — — $ 31,586 70,333 2018 — — — — — — — — — 41,619 Total 685,504 All outstanding liabilities before 2009, net of reinsurance 2,208 Liabilities for losses and loss adjustment expenses, net of reinsurance $ 155,525 Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance Years 1 2 3 4 5 6 7 8 9 10 Unaudited Workers' Compensation Insurance 33.2 % 36.5 % 14.1 % 7.1 % 3.3 % 1.3 % 0.7 % 0.3 % 0.1 % 0.2 % Segregated Portfolio Cell Reinsurance - Workers' Compensation Reserve The Company estimates and reserves for the workers' compensation business assumed by the Segregated Portfolio Cell Reinsurance segment in the same manner as for its workers' compensation business in the Workers' Compensation Insurance segment, as previously discussed. Segregated Portfolio Cell Reinsurance - Workers' Compensation Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2018 ($ in thousands) Year Ended December 31, IBNR* Cumulative Number of Reported Claims 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 Accident Year Unaudited 2009 $ 17,790 $ 16,337 $ 15,886 $ 15,948 $ 15,809 $ 15,695 $ 15,618 $ 15,277 $ 15,277 $ 15,279 $ 107 2,962 2010 — $ 19,767 $ 18,265 $ 17,715 $ 17,825 $ 17,736 $ 17,541 $ 17,320 $ 17,278 17,224 $ 275 2,914 2011 — — $ 18,790 $ 19,360 $ 19,629 $ 19,282 $ 18,644 $ 18,725 $ 18,666 18,606 $ 363 3,154 2012 — — — $ 22,940 $ 21,513 $ 21,048 $ 20,028 $ 19,972 $ 19,864 19,799 $ 441 3,454 2013 — — — — $ 23,809 $ 25,310 $ 26,758 $ 26,619 $ 26,260 26,033 $ 544 3,723 2014 — — — — — $ 28,248 $ 28,423 $ 29,000 $ 28,373 28,281 $ 942 4,433 2015 — — — — — — $ 36,423 $ 32,519 $ 28,746 27,548 $ 1,601 4,949 2016 — — — — — — — $ 37,601 $ 34,055 30,998 $ 2,528 5,326 2017 — — — — — — — — $ 42,725 38,594 $ 7,314 5,699 2018 — — — — — — — — — 43,654 $ 18,788 6,228 Total $ 266,016 * Includes expected development on reported claims Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (In thousands) Year Ended December 31, 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 Accident Year Unaudited 2009 $ 5,000 $ 10,782 $ 13,202 $ 14,660 $ 14,881 $ 14,954 $ 15,147 $ 15,165 $ 15,166 $ 15,172 2010 — $ 6,503 $ 12,904 $ 15,087 $ 16,214 $ 16,757 $ 16,842 $ 16,810 $ 16,850 16,904 2011 — — $ 5,940 $ 14,045 $ 17,197 $ 17,869 $ 18,054 $ 18,177 $ 18,176 18,185 2012 — — — $ 7,808 $ 14,740 $ 17,728 $ 18,474 $ 19,208 $ 19,402 19,328 2013 — — — — $ 8,131 $ 19,054 $ 24,268 $ 25,209 $ 25,366 25,489 2014 — — — — — $ 9,933 $ 21,880 $ 26,173 $ 26,810 26,959 2015 — — — — — — $ 11,257 $ 21,706 $ 23,977 24,781 2016 — — — — — — — $ 10,980 $ 23,003 26,285 2017 — — — — — — — — $ 12,404 24,791 2018 — — — — — — — — — 12,517 Total 210,411 All outstanding liabilities before 2009, net of reinsurance 912 Liabilities for losses and loss adjustment expenses, net of reinsurance $ 56,517 Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance Years 1 2 3 4 5 6 7 8 9 10 Unaudited Segregated Portfolio Cell Reinsurance - Workers' Compensation 34.5 % 38.5 % 14.3 % 4.6 % 1.7 % 0.6 % 0.2 % 0.1 % 0.2 % — % Syndicate 1729 Reserve Given the recent inception date for Syndicate 1729 (January 1, 2014) there is limited reliable historical claims data to use in establishing initial reserves for the exposures in the Lloyd's Syndicates segment. Consequently, ProAssurance estimates initial losses using the loss assumptions by risk category incorporated into the business plan submitted to Lloyd’s with consideration given to loss experience incurred to date. These assumptions are influenced by loss results in Lloyd's historical data for similar risks. In addition, Lloyd's market data for payment patterns is utilized to develop the payout patterns in the tables shown below. As the book of business matures and additional loss information becomes available, the actual loss experience of Syndicate 1729's book of business will be utilized to a greater extent. This will occur sooner for property coverages than for casualty coverages due to the shorter claim reporting and resolution time described above. Claim count information for assumed reinsurance coverage written by Syndicate 1729 is not meaningful in many instances. Certain reinsurance contracts provide aggregate coverage for loss events involving numerous underlying claims, resulting in a single claim count for reinsurance purposes, while other reinsurance contracts provide individual per-claim coverage. Still others may provide aggregate stop loss coverage based on the total losses or loss ratio of a class of business. As a result, claim count information is not included in the Syndicate 1729 Casualty and Syndicate 1729 Property Reinsurance tables shown below. Syndicate 1729 writes coverage in a variety of jurisdictions and currencies, although the majority of its business is in U.S. dollars. For purposes of th

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 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 of Note 1 . 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. ProAssurance had total funding commitments of approximately $297.8 million which primarily represented funding commitments related to non-public investment entities as well as the 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. Of these total funding commitments, $1.0 million is related to qualified affordable housing project tax credit investments and is expected to be paid as follows: $0.2 million in 2019, $0.3 million in 2020 and 2021 combined, $0.4 million in 2022 and 2023 combined and $0.1 million thereafter. As a member of Lloyd's , ProAssurance is required to provide capital to support its Lloyd's Syndicates through 2019 of up to $200.0 million , referred to as FAL . The Board, through a non-binding resolution, extended this commitment through 2022. At December 31, 2018 , ProAssurance's FAL was comprised of investment securities on deposit with Lloyd's with a carrying value of $142.7 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 December 31, 2018 , the unused commitment under the Syndicate Credit Agreement approximated £7.1 million (approximately $9.1 million ). In January 2019, the Syndicate Credit Agreement was amended to extend the current maturity to December 31, 2020 and to implement an annual auto-renewal feature which allows for ProAssurance to elect to non-renew if notice is given at least 30 days prior to the next auto-renewal date, which is one year prior to the maturity date. 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 $4.8 million per year with additional variable quarterly incentive fees based on service utilization metrics prescribed in the contract. ProAssurance incurred operating expense associated with this agreement of $1.0 million in the fourth quarter of 2018 and as of December 31, 2018 , the remaining commitment under this agreement was approximately $8.6 million . ProAssurance is involved in a number of operating leases, primarily for office space. The following is a schedule of future minimum lease payments for operating leases that had initial or remaining non-cancelable lease terms in excess of one year as of December 31, 2018 . Operating Leases (In thousands) 2019 $ 4,829 2020 4,020 2021 3,557 2022 2,618 2023 1,888 Thereafter 10,212 Total minimum lease payments $ 27,124 ProAssurance incurred rent expense of $7.9 million , $6.7 million and $5.9 million in the years ended December 31, 2018 , 2017 and 2016 , respectively.

Debt

Debt	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Debt	Debt ProAssurance’s outstanding debt consisted of the following: (In thousands) December 31, 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%. 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% (4.10% and 2.86%, respectively) determined on a quarterly basis. 39,064 40,460 Total principal 289,064 413,460 Less debt issuance costs 1,307 1,649 Debt less debt issuance costs $ 287,757 $ 411,811 Senior Notes due 2023 (the Senior Notes) The Senior Notes are the unsecured obligations of ProAssurance Corporation, due in full in November 2023, unless redeemed sooner, with interest payable semiannually. Redemptions may be made prior to maturity, in whole or part, at the greater of par or the sum of the present values of the outstanding principal and remaining interest payments calculated at 0.4% above the then current rate for U.S. Treasury Notes with a term comparable to the remaining term of the Senior Notes. There are no financial covenants associated with the Senior Notes. Revolving Credit Agreement ProAssurance has entered into a Revolving Credit Agreement with seven participating lenders with an expiration date of June 2020 . The Revolving Credit Agreement permits ProAssurance to borrow, repay and reborrow from the lenders during the term of the Revolving Credit Agreement ; aggregate outstanding borrowings are not permitted to exceed $250 million at any time, which includes $50 million made available for use, if subscribed successfully, under an accordion feature. All borrowings are required to be repaid prior to the expiration date of the Revolving Credit Agreement . ProAssurance is required to pay a commitment fee, ranging from 0.125% to 0.25% based on ProAssurance’s credit ratings, on the average unused portion of the credit line during the term of the Revolving Credit Agreement . Borrowings under the Revolving Credit Agreement may be secured or unsecured and accrue interest at a selected base rate, adjusted by a margin, which can vary from 0% to 1.63% , based on ProAssurance’s credit ratings and whether the borrowing is secured or unsecured. The base rate selected may either be the current one-, three- or six-month LIBOR , with the LIBOR term selected fixing the interest period for which the rate is effective. If no selection is made, the base rate defaults to the highest of (1) the Prime rate (2) the Federal Funds rate plus 0.5% or (3) the one month LIBOR plus 1.0% , determined daily. Rates are reset each successive interest period until the borrowing is repaid. The Revolving Credit Agreement contains customary representations, covenants and events constituting default, and remedies for default. Additionally, the Revolving Credit Agreement carries the following financial covenants: (1) ProAssurance is not permitted to have a leverage ratio of Consolidated Funded Indebtedness (principally, obligations for borrowed money, obligations evidenced by instruments such as notes or acceptances, standby and commercial Letters of Credit, and contingent obligations) to Consolidated Total Capitalization (principally, total non-trade liabilities on a consolidated basis plus consolidated shareholders’ equity, exclusive of AOCI ) greater than 0.35 to 1.0 , determined at the end of each fiscal quarter. (2) ProAssurance is required to maintain a minimum net worth, excluding AOCI , of at least $1.3 billion . Funds borrowed under the terms of the Revolving Credit Agreement will be used for general corporate purposes, including, but not limited to, use as short-term working capital, funding for share repurchases as authorized by the Board and support for other activities. Mortgage Loans During 2017, two of ProAssurance's subsidiaries each entered into ten -year mortgage loans collectively totaling $40.5 million (Mortgage Loans) with one lender in connection with the recapitalization of two office buildings. The Mortgage Loans, which mature in December 2027 , accrue interest at three-month LIBOR plus 1.325% with principal and interest payable on a quarterly basis. To manage the Company's exposure to increases in LIBOR on the Mortgage Loans, ProAssurance entered into an interest rate cap agreement with a notional amount of $35.0 million . Per the interest rate cap agreement, the Company is entitled to receive cash payments if and when the three-month LIBOR exceeds 2.35% . Additional information on the Company's derivative instruments is provided in Note 11 . The Mortgage Loans contain customary representations, covenants and events constituting default, and remedies for default. Additionally, the Mortgage Loans carry the following financial covenant: (1) Each of the two ProAssurance subsidiaries are not permitted to have a leverage ratio of Consolidated Funded Debt (principally, obligations for borrowed money, obligations for deferred purchase price of property or services, obligations evidenced by notes, bonds, debentures, standby and commercial Letters of Credit and contingent obligations of the subsidiary) to Consolidated Total Capitalization (principally, SAP Consolidated Net Worth plus Consolidated Funded Debt of the subsidiary) greater than 0.35 , determined at the end of each fiscal quarter. At December 31, 2018 , contractual maturities of the Mortgages Loans for each of the next five years, excluding interest payments, are as follows: (In thousands) Principal Payments Due by Period 2019 $ 1,448 2020 1,503 2021 1,559 2022 1,617 2023 1,677 Thereafter 31,260 Total principal payments $ 39,064 Covenant Compliance ProAssurance is currently in compliance with all covenants.

Derivatives

Derivatives	12 Months Ended
	Dec. 31, 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 December 31, 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 10 . Under the terms of the interest rate cap agreement, ProAssurance paid a premium of $2 million in 2017 for the right to receive cash payments based upon a notional amount of $35 million if and when the three-month LIBOR rises above 2.35% . The Company's variable-rate Mortgage Loans bear an interest rate of three-month LIBOR plus 1.325% . Therefore, this derivative instrument is effectively ensuring the interest rate related to the Mortgage Loans is capped at a maximum of 3.675% until expiration of the interest rate cap agreement in October 2027 . ProAssurance has designated the interest rate cap as an economic hedge (non-hedging instrument) of interest rate exposure and any change in fair value of the derivative is immediately recognized in earnings during the period of change. The following table provides a summary of the volume and fair value position of the interest rate cap as well as the reporting location in the Consolidated Balance Sheets as of December 31, 2018 and 2017 . ($ in thousands) December 31, 2018 December 31, 2017 Derivatives Not Designated as Hedging Instruments Location in the 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 $ 1,884 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 Consolidated Statements of Income and Comprehensive Income for the years ended December 31, 2018 , 2017 and 2016 . Gains (Losses) Recognized in Income on Derivatives (In thousands) Year Ended December 31 Derivatives Not Designated as Hedging Instruments Location in the Consolidated Statements of Income and Comprehensive Income 2018 2017 2016 Interest Rate Cap Interest expense $ 153 $ (339 ) $ — 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 December 31, 2018 , the counterparty had an investment grade rating of BBB- and has performed in accordance with their contractual obligations.

Shareholders' Equity

Shareholders' Equity	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Shareholders' Equity	Shareholders’ Equity At December 31, 2018 and 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. The following is a summary of changes in common shares issued and outstanding during the years ended December 31, 2018 , 2017 and 2016 : (In thousands) 2018 2017 2016 Issued and outstanding shares - January 1 53,457 53,251 53,101 Repurchase of shares, at cost of $2 million for 2016 — — (44 ) Shares issued due to exercise of options and vesting of share-based compensation awards 135 132 108 Other shares issued for compensation and shares reissued to stock purchase plan * 45 74 86 Issued and outstanding shares - December 31 53,637 53,457 53,251 * Shares issued were valued at fair value (the market price of a ProAssurance common share on the date of issue). As of December 31, 2018 , approximately 2.0 million of ProAssurance's authorized common shares were reserved by the Board for award or issuance under the incentive compensation plans described in Note 13 and an additional 0.6 million of authorized common shares were reserved for the issuance of currently outstanding restricted share and performance share unit awards. ProAssurance declared cash dividends during 2018 , 2017 and 2016 as follows: Cash Dividends Declared, per Share 2018 2017 2016 First Quarter $ 0.31 $ 0.31 $ 0.31 Second Quarter $ 0.31 $ 0.31 $ 0.31 Third Quarter $ 0.31 $ 0.31 $ 0.31 Fourth Quarter* $ 0.81 $ 5.00 $ 5.00 * Includes special dividends of $0.50 per share in 2018 and $4.69 per share in both 2017 and 2016 . Quarterly dividends were paid in the month following the quarter in which they were declared. Dividends declared during 2018 , 2017 and 2016 totaled $94.3 million , $316.9 million and $315.0 million , respectively. ProAssurance's ability to pay dividends to its shareholders is limited by its holding company structure, to the extent of the net assets held by its insurance subsidiaries, as discussed in Note 18 . Otherwise, there are no other regulatory restrictions on ProAssurance's retained earnings or net income that materially impact its ability to pay dividends. Based on shareholders' equity at December 31, 2018 , total equity of $165.3 million was free of debt covenant restrictions regarding the payment of dividends. However, any decision to pay future cash dividends is subject to the Board’s final determination after a comprehensive review of financial performance, future expectations and other factors deemed relevant by the Board. As of December 31, 2018 , Board authorizations for the repurchase of common shares or the retirement of outstanding debt of $109.6 million remained available for use. The timing and quantity of purchases depends upon market conditions and changes in ProAssurance's capital requirements and is subject to limitations that may be imposed on such purchases by applicable securities laws and regulations as well as the rules of the NYSE . Other Comprehensive Income (Loss) and Accumulated Other Comprehensive Income (Loss) For the years ended December 31, 2018 , 2017 and 2016 , 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 years ended December 31, 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. For the year ended December 31, 2016 , OCI included $1.0 million of unrecognized losses reclassified to earnings, net of tax, due to the termination of one of the defined benefit plans assumed in the Eastern acquisition. At December 31, 2018 and 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 December 31, 2018 and 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 December 31, 2018 and 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: (In thousands) 2018 2017 2016 Reclassifications from AOCI to net income: Realized investment gains (losses) $ 274 $ 2,512 $ 2,417 Non-credit impairment losses reclassified to earnings, due to sale of securities or reclassification as a credit loss (621 ) (3 ) (3,641 ) Unrecognized losses in defined benefit plan liabilities reclassified to earnings, due to the termination and settlement of the plan — — (1,500 ) Total gains (losses) reclassified, before-tax effect (347 ) 2,509 (2,724 ) Tax effect* 73 (878 ) 953 Net reclassification adjustments $ (274 ) $ 1,631 $ (1,771 ) Deferred tax expense (benefit) included in OCI $ (9,573 ) $ (4,676 ) $ (3,078 ) * Tax effects were computed using a 21% for the year ended December 31, 2018 and a 35% rate for the years ended December 31, 2017 and 2016.

Share-Based Payments

Share-Based Payments	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Payments	Share-Based Payments Share-based compensation costs are primarily classified as a component of operating expense. During 2018 , 2017 and 2016 , ProAssurance provided share-based compensation to employees utilizing three types of awards: restricted share units, performance share units and purchase match units. The awards were made under either the ProAssurance Corporation Amended and Restated 2014 Equity Incentive Plan or the ProAssurance Corporation 2008 Equity Incentive Plan. The Compensation Committee of the Board is responsible for the administration of both plans. The following table provides a summary of compensation expense and the total related tax benefit recognized during each period as well as estimated compensation cost that will be charged to expense in future periods. Share-Based Unrecognized Compensation Cost Year Ended December 31 December 31, 2018 ($ in millions, except remaining recognition period) 2018 2017 2016 Amount Weighted Average Remaining Total share-based compensation expense $ 5.3 $ 10.6 $ 12.5 $ 5.9 1.5 Tax benefit recognized $ 1.1 $ 3.7 $ 4.4 The majority of awards are equity classified awards and 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 liability classified awards and are recorded as a liability as they are structured to be settled in cash. As of December 31, 2018 , the majority of share-based compensation expense related to restricted share units. Restricted share 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. Purchase match units vest over a three -year period based on a service requirement with partial vesting permitted for all participants. For the restricted share and purchase match units, a single share is issued per vested unit. For performance share units, the number of shares issued per vested unit varies based on performance goals achieved. For equity classified awards, units sufficient to satisfy required tax withholdings are paid in cash rather than in shares. Liability classified awards, which are nominal in amount, are settled in cash at the end of the vesting period. Restricted Share Units Activity for restricted share units during 2018 , 2017 and 2016 is summarized below. Grant date fair values are based on the market value of a ProAssurance common share on the date of grant less the estimated net present value of dividends during the vesting period. 2018 2017 2016 Units Weighted Units Weighted Units Weighted Beginning non-vested balance 269,520 $ 48.63 240,149 $ 44.07 178,468 $ 43.13 Granted 85,797 $ 44.73 84,565 $ 58.35 109,181 $ 45.59 Forfeited (3,878 ) $ 50.07 (4,087 ) $ 52.35 (5,954 ) $ 43.99 Vested and released (84,116 ) $ 42.90 (51,107 ) $ 43.01 (41,546 ) $ 44.04 Ending non-vested balance 267,323 $ 49.16 269,520 $ 48.63 240,149 $ 44.07 The aggregate grant date fair value of restricted share units vested and released in 2018 , 2017 and 2016 totaled $3.6 million , $2.2 million and $1.8 million , respectively. The aggregate intrinsic value of restricted share units vested and released in 2018 , 2017 and 2016 (including units paid in cash to cover tax withholdings) totaled $4.1 million , $3.1 million and $2.1 million , respectively. Performance Share Units Performance share units vest only if minimum performance objectives are met, and the number of units earned varies from 50% to 200% of a base award depending upon the degree to which stated performance objectives are achieved. Performance share unit activity for 2018 , 2017 and 2016 is summarized below. The table reflects the base number of units; actual awards that vest depend upon the extent to which performance objectives are achieved. Grant date fair values are based on the market value of a ProAssurance common share on the date of grant less the estimated net present value of dividends during the vesting period. 2018 2017 2016 Base Units Weighted Base Units Weighted Base Units Weighted Beginning non-vested balance 212,105 $ 47.11 305,240 $ 43.41 390,350 $ 44.65 Granted 27,202 $ 44.73 48,000 $ 58.35 60,000 $ 45.59 Forfeited — $ — (227 ) $ 42.79 (5,162 ) $ 43.02 Vested and released (104,105 ) $ 42.79 (140,908 ) $ 42.95 (139,948 ) $ 44.05 Ending non-vested balance 135,202 $ 49.95 212,105 $ 47.11 305,240 $ 43.41 The aggregate grant date fair value of performance share units (base level) vested and released in 2018 , 2017 and 2016 totaled $4.5 million , $6.1 million and $6.2 million , respectively. The aggregate intrinsic value of performance share units (base level) vested and released in 2018 , 2017 and 2016 (including units paid in cash to cover tax withholdings) totaled $5.0 million , $8.7 million and $6.9 million , respectively. The weighted average level at which the vested units were issued was 125% , 119% and 98% during 2018 , 2017 and 2016 , respectively, based on performance levels achieved. Purchase Match Units The ProAssurance Corporation 2011 Employee Stock Ownership Plan provides a purchase match unit for each share purchased with contributions by eligible plan participants, with participant contributions subject to a $5,000 annual limit per participant. During 2017, the ProAssurance Corporation 2011 Employee Stock Ownership Plan was discontinued and existing purchase match units will continue to vest according to the vesting period. Purchase match unit activity during 2018 , 2017 and 2016 is summarized below. Grant date fair values are based on the market value of a ProAssurance common share on the date of grant less the estimated net present value of dividends during the vesting period. 2018 2017 2016 Units Weighted Units Weighted Units Weighted Beginning non-vested balance 70,292 $ 49.40 72,615 $ 45.77 74,483 $ 42.80 Granted — $ — 24,444 $ 51.83 23,903 $ 50.18 Forfeited (1,594 ) $ 50.19 (2,012 ) $ 48.29 (2,875 ) $ 43.77 Vested and released (24,016 ) $ 46.28 (24,755 ) $ 41.33 (22,896 ) $ 40.88 Ending non-vested balance 44,682 $ 51.05 70,292 $ 49.40 72,615 $ 45.77 The aggregate grant date fair value of purchase match units vested and released in 2018 , 2017 and 2016 totaled $1.1 million , $1.0 million and $0.9 million , respectively. The aggregate intrinsic value of purchase match share units vested and released in 2018 , 2017 and 2016 (including units paid in cash to cover tax withholdings) totaled $1.1 million , $1.4 million and $1.2 million , respectively. Stock Options ProAssurance also had certain fully-vested employee stock options outstanding during 2016 , as summarized below. ProAssurance had no options exercised during 2018 and 2017 and no outstanding options at December 31, 2018 , 2017 or 2016 . 2018 2017 2016 Options Weighted Options Weighted Options Weighted Outstanding, vested and exercisable, beginning of year — $ — — $ — 2,144 $ 25.02 Exercised — $ — — $ — (2,144 ) $ 25.02 Outstanding, vested and exercisable, end of year — $ — — $ — — $ — The aggregate intrinsic value of options exercised totaled $0.1 million for the year ended December 31, 2016 . There were no cash proceeds from options exercised during the year ended December 31, 2016 .

Variable Interest Entities

Variable Interest Entities	12 Months Ended
	Dec. 31, 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. ProAssurance's VIE interests, carried as a part of investment in unconsolidated subsidiaries, totaled $285.8 million at December 31, 2018 and $269.0 million at December 31, 2017 . ProAssurance's VIE interests, carried as a part of other investments, totaled $33.9 million at December 31, 2017 . 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 9 , ProAssurance has no arrangements with any of the VIE s to provide other financial support to or on behalf of the VIE . At December 31, 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	12 Months Ended
	Dec. 31, 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) Year Ended December 31 2018 2017 2016 Weighted average number of common shares outstanding, basic 53,598 53,393 53,216 Dilutive effect of securities: Restricted Share Units 70 85 73 Performance Share Units 63 110 135 Purchase Match Units 18 23 24 Weighted average number of common shares outstanding, diluted 53,749 53,611 53,448 Effect of dilutive shares on earnings per share $ — $ (0.01 ) $ (0.01 ) 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. The diluted weighted average number of common shares outstanding for the years ended December 31, 2018 and 2017 exclude approximately 2,000 and 7,000 common share equivalents issuable under the Company's stock compensation plans, respectively, as their effect would be antidilutive. There were no common share equivalents that were antidilutive for the year ended December 31, 2016 .

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 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 SPC s 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 SPC s 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 SPC s 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 participants of that cell. ProAssurance participates to a varying degree in the results of selected SPC s. SPC operating results due to external cell participants are reflected as a SPC dividend expense in the Segregated Portfolio Cell Reinsurance segment and in ProAssurance's 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 participants are reflected in the SPC dividend expense. The segment operating results reflects ProAssurance's share of the underwriting and investment results of the SPC s 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 SPC s 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 participants' cumulative undistributed earnings and the results of all SPC s for the current period due to external cell participants 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, other than those reported in the Segregated Portfolio Cell Reinsurance and Lloyd's Syndicates segments, interest expense and U.S. income taxes. 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 described in Note 1 . 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: Year Ended December 31, 2018 (In thousands) Specialty P&C Workers' Compensation Insurance Segregated Portfolio Cell Reinsurance Lloyd's Syndicates Corporate Inter-segment Eliminations Consolidated Net premiums earned $ 491,787 $ 186,079 73,940 $ 67,047 $ — $ — $ 818,853 Net investment income — — 1,566 3,358 86,960 — 91,884 Equity in earnings (loss) of unconsolidated subsidiaries — — — — 8,948 — 8,948 Net realized gains (losses) — — (3,149 ) (460 ) (39,879 ) — (43,488 ) Other income (expense) (1) 5,844 2,412 211 322 3,525 (2,481 ) 9,833 Net losses and loss adjustment expenses (384,431 ) (118,483 ) (38,726 ) (51,570 ) — — (593,210 ) Underwriting, policy acquisition and operating expenses (1) (112,419 ) (55,693 ) (22,426 ) (31,686 ) (18,767 ) 2,435 (238,556 ) Segregated portfolio cells dividend (expense) income — — (9,122 ) — — — (9,122 ) Interest expense — — — — (16,163 ) 46 (16,117 ) Income tax benefit (expense) — — — 317 17,715 — 18,032 Segment operating results $ 781 $ 14,315 $ 2,294 $ (12,672 ) $ 42,339 $ — $ 47,057 Significant non-cash items: Depreciation and amortization, net of accretion $ 7,050 $ 3,850 $ 441 $ (8 ) $ 9,922 $ — $ 21,255 Year Ended December 31, 2017 (In thousands) Specialty P&C Workers' Compensation Insurance Segregated Portfolio Cell Reinsurance Lloyd's Syndicates Corporate Inter-segment Eliminations Consolidated Net premiums earned $ 449,823 $ 163,309 $ 68,197 $ 57,202 $ — $ — $ 738,531 Net investment income — — 1,059 1,736 92,867 — 95,662 Equity in earnings (loss) of unconsolidated subsidiaries — — — — 8,033 — 8,033 Net realized gains (losses) — — 3,914 107 12,388 — 16,409 Other income (expense) (1) 5,688 2,096 115 (1,476 ) 2,888 (1,797 ) 7,514 Net losses and loss adjustment expenses (285,250 ) (102,233 ) (37,455 ) (44,220 ) — — (469,158 ) Underwriting, policy acquisition and operating expenses (1) (107,972 ) (52,576 ) (20,764 ) (26,963 ) (29,275 ) 1,797 (235,753 ) Segregated portfolio cells dividend (expense) income (2) (5,181 ) — (10,590 ) — — — (15,771 ) Interest expense — — — — (16,844 ) — (16,844 ) Income tax benefit (expense) (2) — — — 568 (21,927 ) — (21,359 ) Segment operating results $ 57,108 $ 10,596 $ 4,476 $ (13,046 ) $ 48,130 $ — $ 107,264 Significant non-cash items: Depreciation and amortization, net of accretion $ 7,922 $ 3,480 $ 680 $ (20 ) $ 16,734 $ — $ 28,796 Year Ended December 31, 2016 (In thousands) Specialty P&C Workers' Compensation Insurance Segregated Portfolio Cell Reinsurance Lloyd's Syndicates Corporate Inter-segment Eliminations Consolidated Net premiums earned $ 454,506 $ 161,988 $ 62,137 $ 54,650 $ — $ — $ 733,281 Net investment income — — 711 1,410 97,891 — 100,012 Equity in earnings (loss) of unconsolidated subsidiaries — — — — (5,762 ) — (5,762 ) Net realized gains (losses) — — 2,525 76 32,274 — 34,875 Other income (expense) (1) 5,306 2,218 18 1,415 1,069 (2,218 ) 7,808 Net losses and loss adjustment expenses (266,090 ) (107,791 ) (35,232 ) (34,116 ) — — (443,229 ) Underwriting, policy acquisition and operating expenses (1) (103,656 ) (53,597 ) (18,936 ) (22,832 ) (30,807 ) 2,218 (227,610 ) Segregated portfolio cells dividend (expense) income — — (8,142 ) — — — (8,142 ) Interest expense — — — — (15,032 ) — (15,032 ) Income tax benefit (expense) — — — (384 ) (24,736 ) — (25,120 ) Segment operating results $ 90,066 $ 2,818 $ 3,081 $ 219 $ 54,897 $ — $ 151,081 Significant non-cash items: Depreciation and amortization, net of accretion $ 7,268 $ 5,600 $ 595 $ 132 $ 19,194 $ — $ 32,789 (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 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 2017 related to periods prior to the then current period and was unrelated to the Company's Cayman Islands captive operations. The $1.8 million tax impact of the expense recognized in 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. Year Ended December 31 (In thousands) 2018 2017 2016 Specialty P&C Segment Gross premiums earned: Healthcare professional liability $ 518,303 $ 477,561 $ 474,981 Legal professional liability 26,094 25,771 26,125 Medical technology liability 35,157 33,836 34,158 Other 468 415 667 Ceded premiums earned (88,235 ) (87,760 ) (81,425 ) Segment net premiums earned 491,787 449,823 454,506 Workers' Compensation Insurance Segment Gross premiums earned: Traditional business 199,466 173,246 171,434 Alternative market business 83,508 80,698 75,658 Ceded premiums earned (96,895 ) (90,635 ) (85,104 ) Segment net premiums earned 186,079 163,309 161,988 Segregated Portfolio Cell Reinsurance Segment Gross premiums earned: Workers' compensation (1) 78,255 72,814 66,899 Healthcare professional liability (2) 5,009 4,097 3,310 Ceded premiums earned (9,324 ) (8,714 ) (8,072 ) Segment net premiums earned 73,940 68,197 62,137 Lloyd's Syndicates Segment Gross premiums earned: Property and casualty (3) 83,307 69,749 60,564 Ceded premiums earned (16,260 ) (12,547 ) (5,914 ) Segment net premiums earned 67,047 57,202 54,650 Consolidated net premiums earned $ 818,853 $ 738,531 $ 733,281 (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 $5.0 million , $11.8 million and $14.0 million for years ended December 31, 2018 , 2017 and 2016 , respectively.

Benefit Plans

Benefit Plans	12 Months Ended
	Dec. 31, 2018
Retirement Benefits [Abstract]
Benefit Plans	Benefit Plans ProAssurance maintains the ProAssurance Savings Plan that is intended to provide retirement income to eligible employees. ProAssurance provides employer contributions to the plan of up to 10% of salary for qualified employees. ProAssurance incurred expense related to the ProAssurance Savings Plan of $7.0 million , $7.8 million and $6.9 million during the years ended December 31, 2018 , 2017 and 2016 , respectively. ProAssurance also maintains the ProAssurance Plan that allows participating management employees to defer a portion of their current salary. ProAssurance incurred expense related to the ProAssurance Plan of $0.3 million during each of the years ended December 31, 2018 , 2017 and 2016. ProAssurance deferred compensation liabilities totaled $21.3 million and $20.5 million at December 31, 2018 and 2017 , respectively. The liabilities included amounts due under the ProAssurance Plan and amounts due under individual agreements with current or former employees.

Statutory Accounting and Divide

Statutory Accounting and Dividend Restrictions	12 Months Ended
	Dec. 31, 2018
Insurance [Abstract]
Statutory Accounting and Dividend Restrictions	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 Consolidated Statements of Income and Comprehensive Income for the year ended December 31, 2018 . In addition, ProAssurance recorded a deferred gain of $0.6 million in the reserve for losses and loss adjustment expenses in the second quarter of 2018 representing the excess of premiums received over losses assumed related to the retroactive coverage which is amortized into earnings over the estimated claim payment period. ProAssurance recognized a nominal amount of amortization related to this deferred gain during the year ended December 31, 2018 . For additional information regarding ProAssurance's accounting policy for retroactive insurance contracts, see Note 1 . Statutory Accounting and Dividend Restrictions ProAssurance’s domestic U.S. insurance subsidiaries are required to file statutory financial statements with state insurance regulatory authorities, prepared based upon SAP prescribed or permitted by regulatory authorities. ProAssurance did not use any prescribed or permitted SAP that differed from the NAIC 's SAP at December 31, 2018 , 2017 or 2016 . Differences between net income prepared in accordance with GAAP and statutory net income are principally due to: (a) policy acquisition and certain software and equipment costs which are deferred under GAAP but expensed for statutory purposes and (b) certain deferred income taxes which are recognized under GAAP but are not recognized for statutory purposes. The NAIC specifies risk-based capital requirements for property and casualty insurance providers. At December 31, 2018 , actual statutory capital and surplus for each of ProAssurance’s insurance subsidiaries substantially exceeded the regulatory requirements. Net earnings and capital and surplus of ProAssurance’s insurance subsidiaries on a statutory basis are shown in the following table. (In millions) Statutory Net Earnings Statutory Capital and Surplus 2018 2017 2016 2018 2017 $135 $139 $163 $1,041 $1,175 At December 31, 2018 , $1.3 billion of ProAssurance's consolidated net assets were held at its domestic insurance subsidiaries, of which approximately $128 million are permitted to be paid as dividends over the course of 2019 without prior approval of state insurance regulators. However, the payment of any dividend requires prior notice to the insurance regulator in the state of domicile and the regulator may prevent the dividend if, in its judgment, payment of the dividend would have an adverse effect on the capital and surplus of the insurance subsidiary.

Quarterly Results of Operations

Quarterly Results of Operations (unaudited)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Data [Abstract]
Quarterly Results of Operations (unaudited)	Quarterly Results of Operations (unaudited) The following is a summary of unaudited quarterly results of operations for 2018 and 2017 : 2018* (In thousands, except per share data) 1st 2nd 3rd 4th Net premiums earned $ 187,159 $ 223,591 $ 206,070 $ 202,033 Net losses and loss adjustment expenses: Current year $ 152,572 $ 184,543 $ 169,154 $ 179,056 Favorable development of reserves established in prior years, net $ (22,786 ) $ (22,815 ) $ (21,549 ) $ (24,967 ) Net income (loss) $ 11,856 $ 28,423 $ 31,228 $ (24,450 ) Basic earnings per share $ 0.22 $ 0.53 $ 0.58 $ (0.46 ) Diluted earnings per share $ 0.22 $ 0.53 $ 0.58 $ (0.46 ) 2017* (In thousands, except per share data) 1st 2nd 3rd 4th Net premiums earned $ 182,903 $ 180,353 $ 192,303 $ 182,972 Net losses and loss adjustment expenses: Current year $ 147,927 $ 144,562 $ 161,631 $ 149,399 Favorable development of reserves established in prior years, net $ (28,776 ) $ (29,012 ) $ (32,275 ) $ (44,297 ) Net income (loss) $ 41,455 $ 19,518 $ 28,949 $ 17,342 Basic earnings per share $ 0.78 $ 0.37 $ 0.54 $ 0.32 Diluted earnings per share $ 0.77 $ 0.36 $ 0.54 $ 0.32 *Due to rounding, the sum of quarterly amounts may not equal the total amount for the respective year-to-date periods

Schedule I - Summary of Investm

Schedule I - Summary of Investments - Other Than Investments In Related Parties	12 Months Ended
	Dec. 31, 2018
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Abstract]
Schedule I - Summary of Investments Other than Investments in Related Parties	December 31, 2018 Type of Investment Recorded Fair Amount Which is Fixed maturities Bonds: U.S. Government or government agencies and authorities $ 171,770 $ 170,154 $ 170,154 States, municipalities and political subdivisions 289,544 293,772 293,772 Foreign governments 30,318 29,892 29,892 Public utilities 76,735 76,059 76,059 All other corporate bonds 1,160,474 1,140,356 1,140,356 Certificates of deposit 100 100 100 Mortgage-backed securities 426,329 421,653 421,653 Total Fixed Maturities 2,155,270 2,131,986 2,131,986 Equity Securities Common Stocks: Public utilities 7,553 9,177 9,177 Banks, trusts and insurance companies 64,148 62,344 62,344 Industrial, miscellaneous and all other 379,230 371,416 371,416 Total Equity Securities, trading 450,931 442,937 442,937 Other long-term investments 352,654 466,140 466,140 Short-term investments 308,367 308,319 308,319 Total Investments $ 3,267,222 $ 3,349,382 $ 3,349,382

Schedule II - Condensed Financi

Schedule II - Condensed Financial Information of Registrant	12 Months Ended
	Dec. 31, 2018
Condensed Financial Information Disclosure [Abstract]
Schedule II - Condensed Financial Information of Registrant	December 31, December 31, Assets Investment in subsidiaries, at equity $ 1,599,486 $ 1,713,656 Fixed maturities available for sale, at fair value 78,076 155,094 Short-term investments 76,347 268,181 Investment in unconsolidated subsidiaries 875 1,200 Cash and cash equivalents 25,757 81,009 Due from subsidiaries — 2,666 Other assets 45,683 33,829 Total Assets $ 1,826,224 $ 2,255,635 Liabilities and Shareholders’ Equity Liabilities: Due to subsidiaries $ 4,067 $ — Dividends payable 43,446 267,292 Other liabilities 6,823 22,008 Debt less debt issuance costs 248,886 371,540 Total Liabilities 303,222 660,840 Shareholders’ Equity: Common stock 630 628 Other shareholders’ equity, including unrealized gains (losses) on securities of subsidiaries 1,522,372 1,594,167 Total Shareholders’ Equity 1,523,002 1,594,795 Total Liabilities and Shareholders’ Equity $ 1,826,224 $ 2,255,635 Year Ended December 31 2018 2017 2016 Revenues Net investment income $ 3,495 $ 7,646 $ 6,359 Equity in earnings (loss) of unconsolidated subsidiaries (325 ) (137 ) (155 ) Net realized investment gains (losses) (789 ) (8,606 ) 405 Other income (loss) 977 921 (960 ) Total revenues 3,358 (176 ) 5,649 Expenses Interest expense 14,844 16,440 15,030 Other expenses 17,092 26,351 28,305 Total expenses 31,936 42,791 43,335 Income (loss) before income tax expense (benefit) and equity in net income of consolidated subsidiaries (28,578 ) (42,967 ) (37,686 ) Income tax expense (benefit) (7,142 ) (13,293 ) (12,583 ) Income (loss) before equity in net income of consolidated subsidiaries (21,436 ) (29,674 ) (25,103 ) Equity in net income of consolidated subsidiaries 68,493 136,938 176,184 Net income 47,057 107,264 151,081 Other comprehensive income (loss) (35,238 ) (2,488 ) (6,456 ) Comprehensive income $ 11,819 $ 104,776 $ 144,625 Year Ended December 31 2018 2017 2016 Net cash provided (used) by operating activities $ 27,981 $ 67,779 $ 41,356 Investing activities (Investments in) distributions from unconsolidated subsidiaries, net: Other partnership investments — — (1,000 ) Proceeds from sales or maturities of: Fixed maturities, available for sale 169,822 295,035 100,240 Net decrease (increase) in short-term investments 194,035 11,811 (262,169 ) Dividends from subsidiaries 29,395 99,694 70,125 Contribution of capital to subsidiaries — — (1,983 ) Unsettled security transactions, net of change — 1,100 (1,100 ) Funds (advanced) repaid for Lloyd's FAL deposit (21,576 ) (25,449 ) — Funds (advanced) repaid under Syndicate Credit Agreement (11,232 ) (6,883 ) 1,695 Funds (advanced) repaid under a business investment line of credit — (4,066 ) (3,090 ) Other 330 (2,276 ) (2,805 ) Net cash provided (used) by investing activities 360,774 368,966 (100,087 ) Financing activities Borrowings (repayments) under Revolving Credit Agreement (123,000 ) (77,000 ) 100,000 Repurchase of common stock — — (2,106 ) Subsidiary payments for common shares and share-based compensation awarded to subsidiary employees 1,154 12,030 11,384 Dividends to shareholders (316,476 ) (315,228 ) (118,812 ) Other (5,685 ) (6,868 ) (3,697 ) Net cash provided (used) by financing activities (444,007 ) (387,066 ) (13,231 ) Increase (decrease) in cash and cash equivalents (55,252 ) 49,679 (71,962 ) Cash and cash equivalents at beginning of period 81,009 31,330 103,292 Cash and cash equivalents at end of period $ 25,757 $ 81,009 $ 31,330 Supplemental disclosure of cash flow information: Cash paid during the year for income taxes, net of refunds $ 4,966 $ 17,193 $ (8,519 ) Cash paid during the year for interest $ 14,777 $ 15,892 $ 14,732 Significant non-cash transactions: Dividends declared and not yet paid $ 43,446 $ 267,292 $ 265,659 Securities transferred at fair value as dividends from subsidiaries $ 98,292 $ 190,709 $ 174,270 Basis of Presentation The registrant-only financial statements should be read in conjunction with ProAssurance Corporation’s Consolidated Financial Statements and Notes thereto. At December 31, 2018 and 2017 , PRA investment in subsidiaries is stated at the initial consolidation value plus equity in the undistributed earnings of subsidiaries since the date of acquisition. ProAssurance Corporation has a management agreement with several of its insurance subsidiaries whereby ProAssurance Corporation charges the subsidiaries a management fee for various management services provided to the subsidiary. Under the arrangement, the expenses associated with such services remain as expenses of ProAssurance Corporation and the management fee charged is reported as an offset to ProAssurance Corporation expenses. Prior to 2015, a substantial portion of expenses associated with services provided to insurance subsidiaries were directly allocated or directly charged to the insurance subsidiaries. Reclassifications Effective for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years, ProAssurance Corporation adopted ASU 2016-15 which provides guidance related to the classification of certain cash receipts and cash payments presented in the statement of cash flows. As a result of the adoption, ProAssurance Corporation reclassified approximately $24.4 million and $9.9 million in distributions from unconsolidated subsidiaries from investing activities to operating activities in the registrant-only Condensed Statements of Cash Flow for the years ended December 31, 2017 and 2016 , respectively. See Note 1 of the Notes to Consolidated Financial Statements for additional information.

Schedule III - Supplementary In

Schedule III - Supplementary Insurance Information	12 Months Ended
	Dec. 31, 2018
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Abstract]
Schedule III - Supplementary Insurance Information	2018 2017 2016 Net premiums earned Specialty P&C $ 491,787 $ 449,823 $ 454,506 Workers' Compensation Insurance 186,079 163,309 161,988 Segregated Portfolio Cell Reinsurance 73,940 68,197 62,137 Lloyd's Syndicates 67,047 57,202 54,650 Consolidated $ 818,853 $ 738,531 $ 733,281 Net investment income (1) Segregated Portfolio Cell Reinsurance $ 1,566 $ 1,059 $ 711 Lloyd's Syndicates 3,358 1,736 1,410 Corporate 86,960 92,867 97,891 Consolidated $ 91,884 $ 95,662 $ 100,012 Losses and loss adjustment expenses incurred related to current year, net of reinsurance Specialty P&C $ 461,516 $ 404,543 $ 403,249 Workers' Compensation Insurance 126,534 107,975 109,342 Segregated Portfolio Cell Reinsurance 47,693 45,968 39,801 Lloyd's Syndicates 49,583 45,032 34,615 Consolidated $ 685,326 $ 603,518 $ 587,007 Losses and loss adjustment expenses incurred related to prior year, net of reinsurance Specialty P&C $ (77,085 ) $ (119,293 ) $ (137,159 ) Workers' Compensation Insurance (8,051 ) (5,742 ) (1,551 ) Segregated Portfolio Cell Reinsurance (8,967 ) (8,513 ) (4,569 ) Lloyd's Syndicates 1,987 (812 ) (499 ) Consolidated $ (92,116 ) $ (134,360 ) $ (143,778 ) Paid losses and loss adjustment expenses, net of reinsurance Specialty P&C $ 354,221 $ 320,776 $ 341,189 Workers' Compensation Insurance 108,742 96,734 89,418 Segregated Portfolio Cell Reinsurance 29,320 28,761 27,391 Lloyd's Syndicates 37,496 29,926 21,254 Inter-segment eliminations 200 118 — Consolidated $ 529,979 $ 476,315 $ 479,252 Amortization of DPAC Specialty P&C $ 52,253 $ 47,615 $ 44,344 Workers' Compensation Insurance 16,864 14,551 13,273 Segregated Portfolio Cell Reinsurance 21,039 19,927 18,385 Lloyd's Syndicate 15,913 15,194 13,769 Inter-segment eliminations (1,568 ) (1,536 ) (1,393 ) Consolidated $ 104,501 $ 95,751 $ 88,378 Other underwriting, policy acquisition and operating expenses Specialty P&C $ 60,166 $ 60,357 $ 59,312 Workers' Compensation Insurance 38,829 38,025 40,324 Segregated Portfolio Cell Reinsurance 1,387 837 551 Lloyd's Syndicates 15,773 11,769 9,063 Corporate 18,767 29,275 30,807 Inter-segment eliminations (867 ) (261 ) (825 ) Consolidated $ 134,055 $ 140,002 $ 139,232 Continued on the following page. 2018 2017 2016 Continued from previous page Net premiums written Specialty P&C $ 494,148 $ 466,621 $ 454,718 Workers' Compensation Insurance 195,350 173,566 163,513 Segregated Portfolio Cell Reinsurance 75,547 68,862 64,028 Lloyd's Syndicates 69,869 54,969 56,274 Consolidated $ 834,914 $ 764,018 $ 738,533 Deferred policy acquisition costs (1) $ 54,116 $ 50,261 $ 46,809 Reserve for losses and loss adjustment expenses (1) $ 2,119,847 $ 2,048,381 $ 1,993,428 Unearned premiums (1) $ 415,211 $ 398,884 $ 372,563 (1) Assets are not allocated to segments because investments and assets are not managed at the segment level.

Schedule IV - Reinsurance

Schedule IV - Reinsurance	12 Months Ended
	Dec. 31, 2018
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Abstract]
Schedule IV - Reinsurance	2018 2017 2016 Property and Liability * Premiums earned $ 903,354 $ 821,249 $ 790,791 Premiums ceded (126,036 ) (110,347 ) (95,315 ) Premiums assumed 41,535 27,629 37,805 Net premiums earned $ 818,853 $ 738,531 $ 733,281 Percentage of amount assumed to net 5.07% 3.74% 5.16% * All of ProAssurance’s premiums are related to property and liability coverages.

Accounting Policies (Policies)

Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Organization and Nature of Business	Organization and Nature of Business ProAssurance Corporation (ProAssurance, PRA or the Company), a Delaware corporation, is an insurance holding company primarily for wholly owned specialty property and casualty insurance entities including an entity that is the majority capital provider to Syndicate 1729 and the sole (100%) capital provider of a SPA , Syndicate 6131 at Lloyd's. Risks insured are primarily liability risks located within the U.S. 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 16 .
Principles of Consolidation	Principles of Consolidation The accompanying consolidated financial statements include the accounts of ProAssurance Corporation and its wholly owned subsidiaries. Investments in entities where ProAssurance holds a greater than minor interest but does not hold a controlling interest are accounted for using the equity method. All significant intercompany accounts and transactions are eliminated in consolidation. ProAssurance subsidiaries located in the U.K. are normally reported on a quarter delay due to timing issues regarding the availability of information, except when information is available that is material to the current period. Furthermore, investment results associated with ProAssurance's FAL investments and certain U.S. paid administrative expenses are reported concurrently as that information is available on an earlier time frame.
Basis of Presentation	Basis of Presentation The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, revenues and expenses, and disclosures related to these amounts at the date of the financial statements. Actual results could differ from those estimates.
Reclassifications	Reclassifications As a result of the third quarter of 2018 segment reorganization, prior year segment information in Note 16 has been recast to conform to the Company's current segment reporting (see Note 16 for further information). Certain other insignificant prior year amounts have been reclassified to conform to the current year presentation.
Recognition of Revenues	Recognition of Revenues Insurance premiums are recognized as revenues pro rata over the terms of the policies, which are principally one year in duration. Credit Losses ProAssurance's premium and agency receivables are exposed to credit losses, but to-date have not experienced any significant amount of credit losses. Recorded allowances for credit losses were less than $1.5 million at both December 31, 2018 and 2017 . Neither estimated credit losses nor actual credit write-offs, net of recoveries, exceeded $0.5 million during the years ended December 31, 2018 and 2017 . Earned But Unbilled Premiums Workers’ compensation premiums are determined based upon the payroll of the insured, the applicable premium rates and an experience-based modification factor, where applicable. An audit of the policyholders’ records is conducted after policy expiration to make a final determination of applicable premiums. Audit premium due from or due to a policyholder as a result of an audit is reflected in net premiums written and earned when billed. ProAssurance tracks, by policy, the amount of additional premium billed in final audit invoices as a percentage of payroll exposure and uses this information to estimate the probable additional amount of EBUB premium as of the balance sheet date. Changes to the EBUB estimate are included in net premiums written and earned in the period recognized. As of December 31, 2018 and 2017 , ProAssurance carried EBUB of $4.3 million as a part of premiums receivable. Lloyd’s Premium Estimates For certain insurance policies and reinsurance contracts written in the Lloyd’s Syndicates segment, premiums are initially recognized based upon estimates of ultimate premium. Estimated ultimate premium consists primarily of premium written under delegated underwriting authority arrangements, which consist primarily of binding authorities, and certain assumed reinsurance agreements. These estimates of ultimate premium are judgmental and are dependent upon certain assumptions, including historical premium trends for similar agreements. As reports are received from programs, ultimate premium estimates are revised, if necessary, with changes reflected in current operations.
Losses and Loss Adjustment Expenses	Losses and Loss Adjustment Expenses ProAssurance establishes its reserve for losses and LAE ("reserve for losses" or "reserve") based on estimates of the future amounts necessary to pay claims and expenses associated with the investigation and settlement of claims. The reserve for losses is determined on the basis of individual claims and payments thereon as well as actuarially determined estimates of future losses based on past loss experience, available industry data and projections as to future claims frequency, severity, inflationary trends, judicial trends, legislative changes and settlement patterns. Management establishes the reserve for losses after taking into consideration a variety of factors including premium rates, claims frequency and severity, historical paid and incurred loss development trends, the expected effect of inflation, general economic trends, the legal and political environment and the conclusions reached by internal and consulting actuaries. Management updates and reviews the data underlying the estimation of the reserve for losses each reporting period and makes adjustments to loss estimation assumptions that best reflect emerging data. Both internal and consulting actuaries perform an in-depth review of the reserve for losses on at least a semi-annual basis using the loss and exposure data of ProAssurance's subsidiaries. Consulting actuaries provide reports to management regarding the adequacy of reserves. Estimating casualty insurance reserves, and particularly long-tailed insurance reserves, is a complex process. Long-tailed insurance is characterized by the extended period of time between collecting the premium for insuring a risk and the ultimate payment of losses. For a high proportion of the risks insured or reinsured by ProAssurance, the period of time required to resolve a claim is often five years or more, and claims may be subject to litigation. Estimating losses for these long-tailed claims requires ProAssurance to make and revise judgments and assessments regarding multiple uncertainties over an extended period of time. As a result, reserve estimates may vary significantly from the eventual outcome. Reserve estimates and the assumptions on which these estimates are predicated are regularly reviewed and updated as new information becomes available. Any adjustments necessary are reflected in then current operations. Due to the size of ProAssurance’s reserve for losses, even a small percentage adjustment to these estimates could have a material effect on earnings in the period in which the adjustment is made, as was the case in 2018 , 2017 and 2016 . The effect of adjustments made to reinsured losses is mitigated by the corresponding adjustment that is made to reinsurance recoveries. Thus, in any given year, ProAssurance may make significant adjustments to gross losses that have little effect on its net losses.
Reinsurance Receivables	Reinsurance Receivables ProAssurance enters into reinsurance agreements whereby other insurance entities agree to assume a portion of the risk associated with certain policies issued by ProAssurance. In return, ProAssurance agrees to pay a premium to the reinsurer. ProAssurance uses reinsurance to provide capacity to write larger limits of liability, to provide reimbursement for losses incurred under the higher limit coverages the Company offers, to provide protection against losses in excess of policy limits, and, in the case of risk sharing arrangements, to align the Company's objectives with those of its strategic business partners and to provide custom insurance solutions for large customer groups. Receivable from reinsurers on paid losses and LAE is the estimated amount of losses already paid that will be recoverable from reinsurers. Receivable from reinsurers on unpaid losses and LAE is the estimated amount of future loss payments that will be recoverable from reinsurers. Reinsurance recoveries are the portion of losses incurred during the period that are estimated to be allocable to reinsurers. Premiums ceded are the estimated premiums that will be due to reinsurers with respect to premiums earned and losses incurred during the period. These estimates are based upon management’s estimates of ultimate losses and the portion of those losses that are allocable to reinsurers under the terms of the related reinsurance agreements. Given the uncertainty of the ultimate amounts of losses, these estimates may vary significantly from the ultimate outcome. Management regularly reviews these estimates and any adjustments necessary are reflected in the period in which the estimate is changed. Due to the size of the receivable from reinsurers, even a small adjustment to the estimates could have a material effect on ProAssurance’s results of operations for the period in which the change is made. Reinsurance contracts do not relieve ProAssurance from its obligations to policyholders. ProAssurance continually monitors its reinsurers to minimize its exposure to significant losses from reinsurer insolvencies. Any amount determined to be uncollectible is written off in the period in which the uncollectible amount is identified.
Investments	Investments Recurring Fair Value Measurements Fair values of investment securities are primarily provided by independent pricing services. The pricing services provide an exchange-traded price, if available, or provide an estimated price determined using multiple observable inputs, including exchange-traded prices for similar assets. Management reviews valuations of securities obtained from the pricing services for accuracy based upon the specifics of the security, including class, maturity, credit rating, durations, collateral and comparable markets for similar securities. Multiple observable inputs are not available for certain of the Company's investments, including corporate debt not actively traded, other asset-backed securities and investments in LP s/ LLC s. Management values the corporate debt not actively traded and the other asset-backed securities either using dealer quotes for similar securities or discounted cash flow models using yields currently available for similar securities. Management values certain investment funds, primarily LP s/ LLC s, based on the NAV of the interest held, as provided by the fund. Nonrecurring Fair Value Measurements Management measures the fair value of certain assets on a nonrecurring basis either quarterly, annually or when events or changes in circumstances indicate that the carrying amount of the assets may not be recoverable. These assets include investments carried principally at cost, investments in tax credit partnerships and equity method investments that do not provide a NAV , fixed assets, goodwill and other intangible assets. Fixed Maturities Fixed maturities are considered as either available-for-sale or trading securities. Available-for-sale securities are carried at fair value, determined as described above. Exclusive of OTTI losses, discussed in a separate section that follows, unrealized gains and losses on available-for-sale securities are included, net of related tax effects, in shareholders’ equity as a component of AOCI . Investment income includes amortization of premium and accretion of discount related to available-for-sale debt securities acquired at other than par value. Debt securities and mandatorily redeemable preferred stock with maturities beyond one year when purchased are classified as fixed maturities. Trading securities are carried at fair value, determined as described above, with the holding gains and losses included as a component of net realized investment gains (losses) during the period of change. Equity Investments Equity investments are carried at fair value, as described above, with the holding gains and losses included as a component of net realized investment gains (losses) during the period of change. Equity investments are primarily comprised of stocks, bond funds and investment funds. Short-term Investments 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. All balances are carried at fair value which approximates the cost of the securities due to their short-term nature. Other Investments Investments in convertible bond securities are carried at fair value as permitted by the accounting guidance for hybrid financial instruments, with changes in fair value recognized in income as a component of net realized investment gains (losses) during the period of change. Interest on convertible bond securities is recorded on an accrual basis based on contractual interest rates and is included in net investment income. Investments in certain funds measure fund assets at fair value on a recurring basis and provide ProAssurance with a NAV for its interest. As a practical expedient, ProAssurance considers the NAV provided to approximate the fair value of its interest. Changes in fair value are included as a component of net realized investment gains (losses) during the period of change. Investment in Unconsolidated Subsidiaries Equity investments, primarily investments in LP s/ LLC s, where ProAssurance is deemed to have influence because it holds a greater than a minor interest are accounted for using the equity method. Under the equity method, the recorded basis of the investment is adjusted each period for the investor’s pro rata share of the investee’s income or loss. Investments in unconsolidated subsidiaries include tax credit partnerships accounted for using the equity method, whereby ProAssurance’s proportionate share of income or loss is included in equity in earnings (loss) of unconsolidated subsidiaries. Tax credits received from the partnerships are recognized in the period received as a reduction to current tax expenses. Business Owned Life Insurance ProAssurance owns life insurance contracts on certain management employees. The life insurance contracts are carried at their current cash surrender value. Changes in the cash surrender value are included in income in the current period as investment income. Death proceeds from the contracts are recorded when the proceeds become payable under the policy terms. Realized Gains and Losses Realized investment gains and losses are recognized on the first-in, first-out basis for GAAP purposes and on the specific identification basis for tax purposes. Other-than-temporary Impairments ProAssurance evaluates its available-for-sale investment securities, which at December 31, 2018 and 2017 consisted entirely of fixed maturity securities, on at least a quarterly basis for the purpose of determining whether declines in fair value below recorded cost basis represent OTTI . The Company considers an OTTI to have occurred: • if there is intent to sell the security; • if it is more likely than not that the security will be required to be sold before full recovery of its amortized cost basis; or • if the entire amortized basis of the security is not expected to be recovered. The assessment of whether the amortized cost basis of a security, particularly an asset-backed debt security, is expected to be recovered requires management to make assumptions regarding various matters affecting future cash flows. The choice of assumptions is subjective and requires the use of judgment. Actual credit losses experienced in future periods may differ from management’s estimates of those credit losses. Methodologies used to estimate the present value of expected cash flows are as follows: For non-structured fixed maturities (obligations of states, municipalities and political subdivisions and corporate debt) the estimate of expected cash flows is determined by projecting a recovery value and a recovery time frame and assessing whether further principal and interest will be received. ProAssurance considers various factors in projecting recovery values and recovery time frames, including the following: • third-party research and credit rating reports; • the current credit standing of the issuer, including credit rating downgrades, whether before or after the balance sheet date; • the extent to which the decline in fair value is attributable to credit risk specifically associated with the security or its issuer; • internal assessments and the assessments of external portfolio managers regarding specific circumstances surrounding an investment, which indicate the investment is more or less likely to recover its amortized cost than other investments with a similar structure; • for asset-backed securities, the origination date of the underlying loans, the remaining average life, the probability that credit performance of the underlying loans will deteriorate in the future, and the Company's assessment of the quality of the collateral underlying the loan; • failure of the issuer of the security to make scheduled interest or principal payments; • any changes to the rating of the security by a rating agency; and • recoveries or additional declines in fair value subsequent to the balance sheet date. For structured securities (primarily asset-backed securities), ProAssurance estimates the present value of the security’s cash flows using the effective yield of the security at the date of acquisition (or the most recent implied rate used to accrete the security if the implied rate has changed as a result of a previous impairment or changes in expected cash flows). ProAssurance considers the most recently available six month averages of the levels of delinquencies, defaults, severities, and prepayments for the collateral (loans) underlying the securitization or, if historical data is not available, sector based assumptions, to estimate expected future cash flows of these securities. Exclusive of securities where there is an intent to sell or where it is not more likely than not that the security will be required to be sold before recovery of its amortized cost basis, OTTI for debt securities is separated into a credit component and a non-credit component. The credit component of an OTTI is the difference between the security’s amortized cost basis and the present value of its expected future cash flows, while the non-credit component is the remaining difference between the security’s fair value and the present value of expected future cash flows. The credit component of the OTTI is recognized in earnings while the non-credit component is recognized in OCI . Investments in tax credit partnerships are evaluated for OTTI by considering both qualitative and quantitative factors. These factors include, but are not limited to: • ProAssurance's ability and intent to hold the investment until the recovery of its carrying value; and • in situations where there was not a previous OTTI for the investment, whether the current expected cash flows from the investment, primarily tax benefits, are less than those expected at the time the investment was acquired due to various factors, such as a change in the statutory tax rate; or • in situations where there was a previous OTTI for the investment, whether the expected cash flows from the investment at the time of the OTTI, primarily tax benefits, are less than its current carrying value. Investments which are accounted for under the equity method are evaluated for impairment whenever events or changes in circumstances indicate that the carrying value of the investment may not be recoverable. These circumstances include, but are not limited to, evidence of the inability to recover the carrying value of the investment, the inability of the investee to sustain an earnings capacity that would justify the carrying value of the investment or a current fair value of the investment that is less than the carrying value. ProAssurance recognizes OTTI , exclusive of non-credit OTTI , in earnings as a part of net realized investment gains (losses). In subsequent periods, any measurement of gain, loss or impairment is based on the revised amortized basis of the security. Non-credit OTTI on debt securities and declines in fair value of available-for-sale securities not considered to be other-than-temporary are recognized in OCI . Asset-backed debt securities that have been impaired due to credit reasons or are below investment grade quality are accounted for under the effective yield method. Under the effective yield method, estimates of cash flows expected over the life of asset-backed securities are used to recognize income on the investment balance for subsequent accounting periods.
Derivatives	Derivatives ProAssurance records derivative instruments at fair value in the Consolidated Balance Sheets. ProAssurance accounts for the changes in fair value of derivatives depending on whether the derivative is designated as a hedging instrument and if so, the type of hedging relationship. For derivative instruments not designated as hedging instruments, ProAssurance recognizes the change in fair value of the derivative in earnings during the period of change. As of December 31, 2018 , ProAssurance has not designated any derivative instruments as hedging instruments and does not use derivative instruments for trading purposes.
Foreign Currency	Foreign Currency The functional currency of all ProAssurance foreign subsidiaries is the U.S. dollar. In recording foreign currency transactions, revenue and expense items are converted to U.S. dollars at the exchange rate prevailing at the transaction date. Monetary assets and liabilities originating in currencies other than the U.S. dollar are remeasured to U.S. dollars at the rates of exchange in effect as of the balance sheet date. The resulting foreign currency gains or losses are recognized in the Consolidated Statements of Income and Comprehensive Income as a component of other income. Monetary assets and liabilities include investments, cash and cash equivalents, accrued expenses and other liabilities.
Cash and Cash Equivalents	Cash and Cash Equivalents For purposes of the Consolidated Balance Sheets and Consolidated Statements of Cash Flows, ProAssurance considers all demand deposits and overnight investments to be cash equivalents.
Deferred Policy Acquisition Costs; Ceding Commission Income	Deferred Policy Acquisition Costs; Ceding Commission Income Costs that vary with and are directly related to the successful production of new and renewal premiums (primarily premium taxes, commissions and underwriting salaries) are deferred to the extent they are recoverable against unearned premiums and are amortized as related premiums are earned. Unearned ceding commission income is reported as an offset to DPAC and ceding commission earned is reported as an offset to DPAC amortization.
Income Taxes/Deferred Taxes	Income Taxes/Deferred Taxes ProAssurance files a consolidated federal income tax return. Tax-related interest and penalties are recognized as components of tax expense. ProAssurance evaluates tax positions taken on tax returns and recognizes positions in the financial statements when it is more likely than not that the position will be sustained upon resolution with a taxing authority. If recognized, the benefit is measured as the largest amount of benefit that has a greater than fifty percent probability of being realized. Uncertain tax positions are reviewed each period by considering changes in facts and circumstances, such as changes in tax law, interactions with taxing authorities and developments in case law, and adjustments would be made if considered necessary. Adjustments to unrecognized tax benefits may affect income tax expense and the settlement of uncertain tax positions may require the use of cash. Other than differences related to timing, no significant adjustments were considered necessary during the years ended December 31, 2018 or 2017 . Deferred federal income taxes arise from the recognition of temporary differences between the basis of assets and liabilities determined for financial reporting purposes and the basis determined for income tax purposes. ProAssurance’s temporary differences principally relate to loss reserves, unearned premium, DPAC , unrealized investment gains (losses) and basis differentials in fixed assets and investments. Deferred tax assets and liabilities are measured using the enacted tax rates expected to be in effect when such benefits are realized. ProAssurance reviews its deferred tax assets quarterly for impairment. If management determines that it is more likely than not that some or all of a deferred tax asset will not be realized, a valuation allowance is recorded to reduce the carrying value of the asset. In assessing the need for a valuation allowance, management is required to make certain judgments and assumptions about the future operations of ProAssurance based on historical experience and information as of the measurement date regarding reversal of existing temporary differences, carryback capacity, future taxable income, including its capital and operating characteristics, and tax planning strategies. A valuation allowance has been established against the full value of the deferred tax asset related to the NOL carryforwards for the U.K. operations as management concluded that it was more likely than not that the deferred tax asset will not be realized. In 2018, ProAssurance also established a valuation allowance against the deferred tax assets of certain SPC s at its newly formed wholly owned Cayman Islands reinsurance subsidiary, Inova Re. As of December 31, 2018 , these newly formed SPC s are in a cumulative pre-tax loss position, and management concluded that a valuation allowance was required based upon the weight of this negative evidence. See further discussion in Note 6 . Changes in tax laws and rates could also affect recorded deferred tax assets and liabilities in the future. On December 22, 2017, the TCJA was signed into law and contains several key provisions that impact ProAssurance, including the reduction of the corporate tax rate 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, a change in how property and casualty taxpayers discount loss reserves, a minimum tax on payments made to related foreign entities and a new tax on certain income of controlled foreign corporations. See Note 6 for further discussion of the TCJA .
Real Estate	Real Estate Real Estate balances are reported at cost or, for properties acquired in business combinations, estimated fair value on the date of acquisition, less accumulated depreciation. Real estate principally consists of properties in use as corporate offices. Depreciation is computed over the estimated useful lives of the related property using the straight-line method. Excess office capacity is leased or made available for lease; rental income is included in other income and real estate expenses are included in operating expense.
Intangible Assets	Intangible Assets Intangible assets with definite lives are amortized over the estimated useful life of the asset. Amortizable intangible assets primarily consist of policyholder relationships, renewal rights and trade names. Intangible assets with an indefinite life, primarily state licenses, are not amortized. All intangible assets are evaluated for impairment on an annual basis or upon the occurrence of certain triggering events or substantive changes in circumstances that indicate the fair value of the asset may be impaired.
Goodwill	Goodwill Goodwill is recognized in conjunction with business acquisitions as the excess of the purchase consideration for the business acquisition over the fair value of identifiable assets acquired and liabilities assumed. The fair value of identifiable assets and liabilities, and thus goodwill, is subject to redetermination within a measurement period of up to one year following completion of a business acquisition. Management evaluates goodwill for impairment annually on October 1, upon the occurrence of certain triggering events or substantive changes in circumstances that indicate the fair value of goodwill may be impaired, and immediately before and after a reorganization that affects the composition of one or more of the Company's reporting units. Impairment of goodwill is tested at the reporting unit level, which is consistent with the reportable segments identified in Note 16 . Of the five reporting units, three have goodwill: Specialty P&C, Workers' Compensation Insurance and Segregated Portfolio Cell Reinsurance. Annual Goodwill Impairment Test When testing goodwill for impairment, management has the option to first assess qualitative factors to determine whether the existence of events or circumstances leads to a determination that it is more likely than not that the estimated fair value of a reporting unit is less than its carrying amount. If management elects to perform a qualitative assessment and determines that an impairment is more likely than not, management is then required to perform the two-step quantitative impairment test, otherwise no further analysis is required. Management also may elect not to perform the qualitative assessment and, instead, proceed directly to the two-step quantitative impairment test. As of the most recent annual evaluation date on October 1, 2018, management elected to perform a quantitative goodwill impairment assessment for Specialty P&C, Workers' Compensation Insurance and Segregated Portfolio Cell Reinsurance reporting units. In the first step of the two-step quantitative impairment test, the fair value of a reporting unit is determined using income and market approaches and is compared to its carrying value, as described above. The estimate of fair value derived from the income approach is based on the present value of expected future cash flows, including terminal value, utilizing a market based weighted average cost of capital determined separately for each reporting unit. The estimate of fair value derived from the market approach is based on earnings multiple data derived from market information. The determination of fair value involves the use of significant estimates and assumptions, including revenue growth rates, operating margins, capital expenditures, working capital requirements, tax rates, terminal growth rates, discount rates, comparable public companies and synergistic benefits available to market participants. In addition, management makes certain judgments and assumptions in allocating shared assets and liabilities to individual reporting units to determine the carrying amount of each reporting unit. To corroborate the reporting units’ valuation, management performs a reconciliation of the estimate of the aggregate fair value of the reporting units to ProAssurance's market capitalization, including consideration of a control premium. Because not all of ProAssurance's reporting units have goodwill, management makes certain assumptions regarding the fair value of the Company's other reporting units in reconciling to ProAssurance's market capitalization. If the carrying value of a reporting unit exceeds its fair value, the second step of the impairment test is performed for purposes of measuring the impairment of goodwill, if any. In the second step, the fair value of the reporting unit is allocated to all of the assets and liabilities of the reporting unit to determine an implied fair value of goodwill. If the carrying amount of the reporting unit's goodwill exceeds the implied fair value of goodwill, an impairment loss will be recognized in an amount equal to that excess. As a result of the quantitative assessments performed on October 1, 2018, management concluded that the fair value of each of the Company's three reporting units that have goodwill were greater than their carrying value as of the testing date; therefore, goodwill was not impaired and no further impairment testing was required. No goodwill impairment was recorded in 2018 , 2017 or 2016 . Goodwill Impairment Test - Result of Segment Reorganization As discussed in Note 16 , ProAssurance reorganized its segment reporting in the third quarter of 2018 to align with how the Company's 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 also became a reporting unit for purposes of testing goodwill for impairment. Management allocated goodwill to the Company's revised reporting units using a relative fair value approach which resulted in a nominal amount of goodwill reallocated from the Workers' Compensation Insurance reporting unit to the Segregated Portfolio Cell Reinsurance reporting unit. Management performed a quantitative goodwill impairment assessment for the Workers' Compensation Insurance reporting unit immediately prior to the reallocation and a quantitative goodwill impairment assessment for the Workers' Compensation Insurance and Segregated Portfolio Cell Reinsurance reporting units immediately after the reallocation and determined that no impairment existed. Management estimated the fair value of the Workers' Compensation Insurance and Segregated Portfolio Cell Reinsurance reporting units using both an income approach and market approach using the same valuation methodologies and process for developing assumptions that management uses in the annual impairment assessment, as discussed above. To corroborate the reporting units’ valuation, management performed a reconciliation of the estimate of the aggregate fair value of the reporting units to ProAssurance's market capitalization, including consideration of a control premium. Because management was not required to estimate the fair value of all of the Company's reporting units as part of this interim goodwill impairment assessment, management made certain assumptions regarding the fair value of the Company's other reporting units in reconciling to ProAssurance's market capitalization. The Specialty P&C reporting unit's net operating results were not impacted by the segment reorganization and there was no change to the amount of goodwill allocated to that reporting unit. Consequently, a quantitative goodwill impairment assessment was not required for this reporting unit due to the segment reorganization.
Treasury Shares	Treasury Shares Treasury shares are reported at cost, and are reflected on the Consolidated Balance Sheets as an unallocated reduction of total equity.
Share-Based Payments	Share-Based Payments Compensation cost for share-based payments is measured based on the grant-date fair value of the award, recognized over the period in which the employee is required to provide service in exchange for the award. Excess tax benefits (tax deductions realized in excess of the compensation costs recognized for the exercise of the awards, multiplied by the incremental tax rate) are reported as operating cash inflows.
Subsequent Events	Subsequent Events ProAssurance evaluates events that occurred subsequent to December 31, 2018 , for recognition or disclosure in its Consolidated Financial Statements.
Accounting Changes Adopted and Accounting Changes Not Yet Adopted	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 prospective application and plans to elect the transition option provided that allows companies to continue to apply legacy GAAP in comparative periods. Also, ProAssurance plans to elect the package of practical expedients permitted under the guidance, which allows the Company to carryforward its historical lease classification, its assessment on whether a contract is or contains a lease and its initial direct costs for any leases that exist prior to adoption of the new standard. Furthermore, ProAssurance plans to elect to combine lease and non-lease components and to keep leases with an initial term of 12 months or less off the Consolidated Balance Sheet and recognize the associated lease payments in the Consolidated Statements of Income and Comprehensive Income on a straight-line basis over the lease term. ProAssurance estimates approximately $19 million that would be recognized upon adoption as total right-of-use assets and total lease liabilities on the Consolidated Balance Sheet as of January 1, 2019 which relate to ProAssurance's real estate operating leases; the Company does not consider these leases to be material to its financial position. Adoption of this guidance will have no material impact on ProAssurance's results of operation or cash flows. ProAssurance's Revolving Credit Agreement contains a financial covenant regarding permitted leverage ratios based upon Consolidated Funded Indebtedness to Consolidated Total Capitalization; however, adoption of this guidance would have no material impact on this 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 found in ASU 2016-02, adoption of the guidance would have no impact on this 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 December 31, 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. Derivatives and Hedging - Inclusion of the Secured Overnight Financing Rate (SOFR) Overnight Index Swap as a Benchmark Interest Rate for Hedge Accounting Purposes ( ASU 2018-16) Effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years, the FASB issued new guidance that permits the use of the Overnight Index Swap Rate based on the Secured Financing Rate as a U.S. benchmark interest rate for hedge accounting purposes. ProAssurance plans to adopt the guidance beginning January 1, 2019. ProAssurance's derivative instrument at December 31, 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 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 December 31, 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. Targeted Improvements to Related Party Guidance for VIE s ( ASU 2018-17) Effective for fiscal years beginning after December 15, 2019 and interim periods within those fiscal years, the FASB amended guidance which improves the consistency of the application of the VIE guidance for common control arrangements. The amended guidance requires an entity to consider indirect interests held through related parties under common control on a proportional basis rather than as the equivalent of a direct interest in its entirety when determining whether a decision-making fee is a variable interest. ProAssurance plans to adopt the guidance beginning January 1, 2020. As of December 31, 2018 ProAssurance does not have any material indirect interests held through related parties under common control; therefore, adoption is not expected to have a material effect on ProAssurance’s results of operations, financial position or cash flows. Collaborative Arrangements ( ASU 2018-18) Effective for fiscal years beginning after December 15, 2019 and interim periods within those fiscal years, the FASB issued new guidance which clarifies how to assess whether certain transactions between participants in a collaborative arrangement should be accounted for under the revenue from contracts with customers accounting standard when the counterpart is a customer. In addition, the guidance precludes an entity from presenting consideration from a transaction in a collaborative arrangement as revenue from contracts with customers if the counterparty is not a customer for that transaction. ProAssurance plans to adopt the guidance 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.

Accounting Policies (Tables)

Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Schedule of non-amortizable intangible assets	The following table provides additional information regarding ProAssurance's intangible assets. Gross Carrying Value Accumulated Amortization Amortization Expense December 31 December 31 Year Ended December 31 (In millions) 2018 2017 2018 2017 2018 2017 2016 Intangible Assets Non-amortizable $ 25.8 $ 25.8 Amortizable 97.5 97.5 $ 46.5 $ 40.3 $ 6.2 $ 5.8 $ 8.1 Total Intangible Assets $ 123.3 $ 123.3
Schedule of amortizable intangible assets	The following table provides additional information regarding ProAssurance's intangible assets. Gross Carrying Value Accumulated Amortization Amortization Expense December 31 December 31 Year Ended December 31 (In millions) 2018 2017 2018 2017 2018 2017 2016 Intangible Assets Non-amortizable $ 25.8 $ 25.8 Amortizable 97.5 97.5 $ 46.5 $ 40.3 $ 6.2 $ 5.8 $ 8.1 Total Intangible Assets $ 123.3 $ 123.3
Schedule of other liabilities	Other liabilities at December 31, 2018 and 2017 consisted of the following: (In thousands) 2018 2017 SPC dividends payable $ 53,604 $ 46,925 Unpaid dividends 43,446 267,292 All other 102,245 123,383 Total other liabilities $ 199,295 $ 437,600

Fair Value Measurement (Tables)

Fair Value Measurement (Tables)	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Assets and liabilities measured at fair value	Fair values of assets measured at fair value on a recurring basis as of December 31, 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. December 31, 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 $ — $ 120,201 $ — $ 120,201 U.S. Government-sponsored enterprise obligations — 35,354 — 35,354 State and municipal bonds — 293,772 — 293,772 Corporate debt, multiple observable inputs 2,319 1,216,834 — 1,219,153 Corporate debt, limited observable inputs — — 4,322 4,322 Residential mortgage-backed securities — 181,238 — 181,238 Agency commercial mortgage-backed securities — 13,108 — 13,108 Other commercial mortgage-backed securities — 30,993 — 30,993 Other asset-backed securities — 191,807 3,850 195,657 Fixed maturities, trading — 38,188 — 38,188 Equity investments Financial 62,344 — — 62,344 Utilities/Energy 46,533 — — 46,533 Consumer oriented 47,462 — — 47,462 Industrial 41,487 — — 41,487 Bond funds 174,753 — — 174,753 All other 50,066 — — 50,066 Short-term investments 265,910 42,409 — 308,319 Other investments — 31,341 3 31,344 Other assets — 1,884 — 1,884 Total assets categorized within the fair value hierarchy $ 690,874 $ 2,197,129 $ 8,175 2,896,178 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 20,292 Investment in unconsolidated subsidiaries 268,436 Total assets at fair value $ 3,184,906 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
Summary of quantitative information about Level 3 fair value measurements	Quantitative Information Regarding Level 3 Valuations Fair Value at ($ in thousands) December 31, 2018 December 31, 2017 Valuation Technique Unobservable Input Range Assets: Corporate debt, limited observable inputs $4,322 $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 $3,850 $4,986 Market Comparable Comparability Adjustment 0% - 5% (2.5%) Discounted Cash Flows Comparability Adjustment 0% - 5% (2.5%) Other investments $3 $409 Discounted Cash Flows Comparability Adjustment 0% - 10% (5%)
Summary of changes in the fair value of assets measured at fair value	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. December 31, 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 (148 ) 2 — (146 ) Net realized investment gains (losses) (8 ) — (40 ) (48 ) Included in other comprehensive income (233 ) (105 ) — (338 ) Purchases 8,005 20,093 — 28,098 Sales (6,406 ) (438 ) (366 ) (7,210 ) Transfers in 2,627 — — 2,627 Transfers out (13,218 ) (20,688 ) — (33,906 ) Balance December 31, 2018 $ 4,322 $ 3,850 $ 3 $ 8,175 Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end $ — $ — $ — $ — December 31, 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 (163 ) — — (163 ) Net realized investment gains (losses) 13 — (143 ) (130 ) Included in other comprehensive income (369 ) (71 ) 140 (300 ) Purchases 13,016 2,627 — 15,643 Sales (4,837 ) — (912 ) (5,749 ) Transfers in 999 — 1,321 2,320 Transfers out (9,766 ) (577 ) — (10,343 ) Balance December 31, 2017 $ 13,703 $ 4,986 $ 409 $ 19,098 Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end $ — $ — $ — $ —
Investments in limited liability companies and limited partnerships	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 December 31, 2018 and fair values of these investments as of December 31, 2018 and 2017 was as follows: Unfunded Fair Value (In thousands) December 31, December 31, December 31, Equity investments: Mortgage fund (1)* $ — $ 20,292 $ — Investment in unconsolidated subsidiaries: Private debt funds (2) $ 20,954 18,196 42,206 Long equity fund (3) None 6,561 7,847 Long/short equity funds (4) None 28,805 31,352 Non-public equity funds (5) $ 80,076 114,811 100,062 Multi-strategy fund of funds (6) None 9,322 9,100 Credit funds (7) $ 8,916 29,164 6,561 Long/short commodities fund (8) None 12,958 13,025 Strategy focused funds (9) $ 24,539 48,619 606 268,436 210,759 Other investments: Mortgage fund (1)* See above — 20,130 Total investments carried at NAV $ 288,728 $ 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 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 December 31, 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) This 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) This 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) This 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) This 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) This 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) This investment is comprised of multiple unrelated LPs/LLCs 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 LPs, one of which allows for redemption with prior notice.
Financial instruments not measured at fair value	The following table provides the estimated fair value of ProAssurance's 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. December 31, 2018 December 31, 2017 (In thousands) Carrying Fair Carrying Fair Financial assets: BOLI $ 64,096 $ 64,096 $ 62,113 $ 62,113 Other investments $ 2,943 $ 2,943 $ 58,546 $ 69,095 Other assets $ 35,921 $ 35,468 $ 34,020 $ 33,742 Financial liabilities: Senior notes due 2023* $ 250,000 $ 264,810 $ 250,000 $ 273,153 Revolving Credit Agreement* $ — $ — $ 123,000 $ 123,000 Mortgage Loans* $ 39,064 $ 39,064 $ 40,460 $ 40,460 Other liabilities $ 21,300 $ 21,300 $ 21,154 $ 21,154 * Carrying value excludes debt issuance costs.

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Schedule of amortized cost and estimated fair value of available-for-sale fixed maturities and equity securities	Available-for-sale fixed maturities at December 31, 2018 and December 31, 2017 included the following: December 31, 2018 (In thousands) Amortized Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Fixed maturities, available for sale U.S. Treasury obligations $ 121,274 $ 331 $ 1,404 $ 120,201 U.S. Government-sponsored enterprise obligations 35,758 25 429 35,354 State and municipal bonds 289,544 4,877 649 293,772 Corporate debt 1,244,577 3,328 24,430 1,223,475 Residential mortgage-backed securities 184,463 814 4,039 181,238 Agency commercial mortgage-backed securities 13,296 12 200 13,108 Other commercial mortgage-backed securities 31,330 38 375 30,993 Other asset-backed securities 196,583 254 1,180 195,657 $ 2,116,825 $ 9,679 $ 32,706 $ 2,093,798 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 December 31, 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 $ 121,274 $ 27,187 $ 74,196 $ 18,416 $ 402 $ 120,201 U.S. Government-sponsored enterprise obligations 35,758 3,279 12,301 19,640 134 35,354 State and municipal bonds 289,544 10,506 126,225 129,118 27,923 293,772 Corporate debt 1,244,577 147,223 726,570 324,467 25,215 1,223,475 Residential mortgage-backed securities 184,463 181,238 Agency commercial mortgage-backed securities 13,296 13,108 Other commercial mortgage-backed securities 31,330 30,993 Other asset-backed securities 196,583 195,657 $ 2,116,825 $ 2,093,798
Schedule of investments held in a loss position	The following tables provide summarized information with respect to investments held in an unrealized loss position at December 31, 2018 and December 31, 2017 , including the length of time the investment had been held in a continuous unrealized loss position. December 31, 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 $ 97,969 $ 1,405 $ 20,221 $ 119 $ 77,748 $ 1,286 U.S. Government-sponsored enterprise obligations 33,677 429 20,479 126 13,198 303 State and municipal bonds 63,094 648 30,924 143 32,170 505 Corporate debt 938,651 24,429 447,891 8,804 490,760 15,625 Residential mortgage-backed securities 157,120 4,039 27,311 209 129,809 3,830 Agency commercial mortgage-backed securities 9,822 200 4,566 22 5,256 178 Other commercial mortgage-backed securities 22,924 375 13,348 164 9,576 211 Other asset-backed securities 142,470 1,181 70,218 236 72,252 945 $ 1,465,727 $ 32,706 $ 634,958 $ 9,823 $ 830,769 $ 22,883 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 sales and purchases of fixed maturity available-for-sale securities	Other information regarding sales and purchases of fixed maturity available-for-sale securities is as follows: Year Ended December 31 (In millions) 2018 2017 2016 Proceeds from sales (exclusive of maturities and paydowns) $ 599.6 $ 530.2 $ 361.8 Purchases $ 780.7 $ 614.4 $ 636.4
Schedule of net investment income	Net investment income by investment category was as follows: Year Ended December 31 (In thousands) 2018 2017 2016 Fixed maturities $ 69,515 $ 75,669 $ 85,818 Equities 21,418 17,198 14,887 Short-term investments, including Other 5,649 7,793 3,402 BOLI 1,983 1,979 2,008 Investment fees and expenses (6,681 ) (6,977 ) (6,103 ) Net investment income $ 91,884 $ 95,662 $ 100,012
Schedule of investment in unconsolidated subsidiaries	ProAssurance's investment in unconsolidated subsidiaries were as follows: December 31, 2018 Carrying Value (In thousands) Percentage December 31, December 31, Qualified affordable housing project tax credit partnerships See below $ 65,677 $ 84,607 Other tax credit partnerships See below 3,757 6,118 All other investments, primarily investment fund LPs/LLCs See below 298,323 239,866 $ 367,757 $ 330,591
Schedule of equity method investments	Losses recorded and tax credits recognized related to ProAssurance's tax credit partnership investments were as follows: Year Ended December 31 (In thousands) 2018 2017 2016 Qualified affordable housing project tax credit partnerships Losses recorded $ 18,889 $ 14,297 $ 20,047 Tax credits recognized $ 18,474 $ 17,774 $ 18,531 Historic tax credit partnerships Losses recorded $ 5,434 $ 6,355 $ 4,771 Tax credits recognized $ 2,567 $ 5,337 $ 9,018
Schedule of net realized investment gains (losses)	The following table provides detailed information regarding net realized investment gains (losses): Year Ended December 31 (In thousands) 2018 2017 2016 Total OTTI losses: State and municipal bonds $ — $ (850 ) $ (100 ) Corporate debt (490 ) (419 ) (7,604 ) Investment in unconsolidated subsidiaries — (11,931 ) — Other investments — — (3,130 ) Portion of OTTI losses recognized in other comprehensive income before taxes: Corporate debt — 248 1,068 Net impairment losses recognized in earnings (490 ) (12,952 ) (9,766 ) Gross realized gains, available-for-sale fixed maturities 5,942 6,653 12,451 Gross realized (losses), available-for-sale fixed maturities (5,799 ) (3,123 ) (7,038 ) Net realized gains (losses), short-term investments (1 ) (2 ) 18 Net realized gains (losses), trading fixed maturities (100 ) — — Net realized gains (losses), equity investments 12,230 10,724 6,632 Net realized gains (losses), other investments 1,340 2,963 1,115 Change in unrealized holding gains (losses), trading fixed maturities (317 ) — — Change in unrealized holding gains (losses), equity investments (52,707 ) 11,243 30,557 Change in unrealized holding gains (losses), convertible securities, carried at fair value (3,849 ) 896 899 Other 263 7 7 Net realized investment gains (losses) $ (43,488 ) $ 16,409 $ 34,875
Schedule of cumulative credit losses recorded in earnings related to impaired debt securities for which a portion of the OTTI has been 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 . (In thousands) 2018 2017 2016 Balance beginning of period $ 1,313 $ 1,158 $ 5,751 Additional credit losses recognized during the period, related to securities for which: No OTTI has been previously recognized — 171 2,398 OTTI has been previously recognized — — 2,154 Reductions due to: Securities sold during the period (realized) (1,220 ) (16 ) (9,145 ) Balance December 31 $ 93 $ 1,313 $ 1,158

Reinsurance (Tables)

Reinsurance (Tables)	12 Months Ended
	Dec. 31, 2018
Insurance [Abstract]
Summary of the effect of reinsurance on premiums written and earned	The effects of reinsurance for the years ended December 31, 2018 , 2017 and 2016 were as follows: Year Ended December 31 (In thousands) 2018 2017 2016 Direct $ 910,198 $ 842,968 $ 794,377 Assumed 47,113 31,908 40,637 Ceded (122,397 ) (110,858 ) (96,481 ) Net premiums written $ 834,914 $ 764,018 $ 738,533 Direct $ 903,354 $ 821,249 $ 790,791 Assumed 41,535 27,629 37,805 Ceded (126,036 ) (110,347 ) (95,315 ) Net premiums earned $ 818,853 $ 738,531 $ 733,281 Losses and loss adjustment expenses $ 675,784 $ 592,218 $ 515,242 Reinsurance recoveries (82,574 ) (123,060 ) (72,013 ) Net losses and loss adjustment expenses $ 593,210 $ 469,158 $ 443,229

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Summary of components of deferred tax assets and liabilities	Significant components of ProAssurance’s deferred tax assets and liabilities were as follows: December 31 (In thousands) 2018 2017 Deferred tax assets Unpaid loss discount $ 30,629 $ 20,368 Unearned premium adjustment 16,620 14,449 Compensation related 9,879 11,467 Unrealized losses on investments, net 4,403 — Basis differentials–investments 912 — Intangibles 433 514 Foreign NOL 6,795 4,116 Total gross deferred tax assets 69,671 50,914 Valuation allowance (7,074 ) (4,116 ) Total deferred tax assets, net of valuation allowance 62,597 46,798 Deferred tax liabilities Deferred policy acquisition costs (9,972 ) (6,333 ) Unpaid loss discount–transition (10,128 ) — Unrealized gains on investments, net — (5,166 ) Fixed assets (542 ) (826 ) Basis differentials–investments — (10,397 ) Intangibles (11,243 ) (12,548 ) Other (1,604 ) (1,598 ) Total deferred tax liabilities (33,489 ) (36,868 ) Net deferred tax assets (liabilities) $ 29,108 $ 9,930
Summary of reconciliation of unrecognized tax benefits	A reconciliation of the beginning and ending amounts of unrecognized tax benefits for 2018 , 2017 and 2016 , were as follows: (In thousands) 2018 2017 2016 Balance at January 1 $ 5,341 $ 8,353 $ 8,195 Increases for tax positions taken during the current year — — 361 (Decreases) for tax positions taken during the current year (777 ) (3,500 ) — (Decreases)/increases for tax positions taken during prior years (800 ) 700 — (Decreases) relating to a lapse of the applicable statute of limitations (163 ) (212 ) (203 ) Balance at December 31 $ 3,601 $ 5,341 $ 8,353
Summary of components of tax expense	Income tax expense (benefit) for each of the years ended December 31, 2018 , 2017 and 2016 consisted of the following: (In thousands) 2018 2017 2016 Provision for income taxes Current expense (benefit) Federal and foreign $ (6,509 ) $ 19,546 $ 15,857 State 301 120 729 Total current expense (benefit) (6,208 ) 19,666 16,586 Deferred expense (benefit) Federal and foreign (11,765 ) 1,331 8,284 State (59 ) 362 250 Total deferred expense (benefit) (11,824 ) 1,693 8,534 Total income tax expense (benefit) $ (18,032 ) $ 21,359 $ 25,120
Summary of reconciliation of expected income tax expense to actual income tax expense	A reconciliation of “expected” income tax expense (benefit) (21% of income before income taxes for 2018; 35% of income before income taxes for 2017 and 2016) to actual income tax expense (benefit) for each of the years ended December 31, 2018 , 2017 and 2016 were as follows: (In thousands) 2018 2017 2016 Computed “expected” tax expense $ 6,095 $ 45,018 $ 61,670 Tax-exempt income (2,505 ) (8,356 ) (9,917 ) Tax credits (21,059 ) (23,111 ) (27,549 ) Non-U.S. operating results 2,269 918 (1,688 ) Excess tax benefit on share-based compensation (275 ) (2,762 ) — Change in federal corporate tax rate — 6,541 — Change in limitation of future deductibility of certain executive compensation — 3,497 — Provision-to-return differences (2,309 ) (1,979 ) 1,209 Other (248 ) 1,593 1,395 Total income tax expense (benefit) $ (18,032 ) $ 21,359 $ 25,120

Reserve for Losses and Loss A_2

Reserve for Losses and Loss Adjustment Expenses (Tables)	12 Months Ended
	Dec. 31, 2018
Insurance [Abstract]
Schedule of reserve for losses and loss adjustment expenses	Activity in the reserve for losses and loss adjustment expenses is summarized as follows: (In thousands) 2018 2017 2016 Balance, beginning of year $ 2,048,381 $ 1,993,428 $ 2,005,326 Less reinsurance recoverables on unpaid losses and loss adjustment expenses 335,585 273,475 249,350 Net balance, beginning of year 1,712,796 1,719,953 1,755,976 Net losses: Current year* 685,326 603,518 587,007 Favorable development of reserves established in prior years, net (92,116 ) (134,360 ) (143,778 ) Total 593,210 469,158 443,229 Paid related to: Current year (117,268 ) (106,633 ) (96,190 ) Prior years (412,711 ) (369,682 ) (383,062 ) Total paid (529,979 ) (476,315 ) (479,252 ) Net balance, end of year 1,776,027 1,712,796 1,719,953 Plus reinsurance recoverables on unpaid losses and loss adjustment expenses 343,820 335,585 273,475 Balance, end of year $ 2,119,847 $ 2,048,381 $ 1,993,428 * Current year net losses in 2018 included incurred losses of $25.4 million related to a loss portfolio transfer entered into during the second quarter of 2018 (see Note 4).
Schedule of short-duration insurance contracts claims development	Segregated Portfolio Cell Reinsurance - Workers' Compensation Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2018 ($ in thousands) Year Ended December 31, IBNR* Cumulative Number of Reported Claims 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 Accident Year Unaudited 2009 $ 17,790 $ 16,337 $ 15,886 $ 15,948 $ 15,809 $ 15,695 $ 15,618 $ 15,277 $ 15,277 $ 15,279 $ 107 2,962 2010 — $ 19,767 $ 18,265 $ 17,715 $ 17,825 $ 17,736 $ 17,541 $ 17,320 $ 17,278 17,224 $ 275 2,914 2011 — — $ 18,790 $ 19,360 $ 19,629 $ 19,282 $ 18,644 $ 18,725 $ 18,666 18,606 $ 363 3,154 2012 — — — $ 22,940 $ 21,513 $ 21,048 $ 20,028 $ 19,972 $ 19,864 19,799 $ 441 3,454 2013 — — — — $ 23,809 $ 25,310 $ 26,758 $ 26,619 $ 26,260 26,033 $ 544 3,723 2014 — — — — — $ 28,248 $ 28,423 $ 29,000 $ 28,373 28,281 $ 942 4,433 2015 — — — — — — $ 36,423 $ 32,519 $ 28,746 27,548 $ 1,601 4,949 2016 — — — — — — — $ 37,601 $ 34,055 30,998 $ 2,528 5,326 2017 — — — — — — — — $ 42,725 38,594 $ 7,314 5,699 2018 — — — — — — — — — 43,654 $ 18,788 6,228 Total $ 266,016 * Includes expected development on reported claims Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (In thousands) Year Ended December 31, 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 Accident Year Unaudited 2009 $ 5,000 $ 10,782 $ 13,202 $ 14,660 $ 14,881 $ 14,954 $ 15,147 $ 15,165 $ 15,166 $ 15,172 2010 — $ 6,503 $ 12,904 $ 15,087 $ 16,214 $ 16,757 $ 16,842 $ 16,810 $ 16,850 16,904 2011 — — $ 5,940 $ 14,045 $ 17,197 $ 17,869 $ 18,054 $ 18,177 $ 18,176 18,185 2012 — — — $ 7,808 $ 14,740 $ 17,728 $ 18,474 $ 19,208 $ 19,402 19,328 2013 — — — — $ 8,131 $ 19,054 $ 24,268 $ 25,209 $ 25,366 25,489 2014 — — — — — $ 9,933 $ 21,880 $ 26,173 $ 26,810 26,959 2015 — — — — — — $ 11,257 $ 21,706 $ 23,977 24,781 2016 — — — — — — — $ 10,980 $ 23,003 26,285 2017 — — — — — — — — $ 12,404 24,791 2018 — — — — — — — — — 12,517 Total 210,411 All outstanding liabilities before 2009, net of reinsurance 912 Liabilities for losses and loss adjustment expenses, net of reinsurance $ 56,517 Medical Technology Liability Claims-Made Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2018 ($ in thousands) Year Ended December 31, IBNR* Cumulative Number of Reported Claims 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 Accident Year Unaudited 2009 $ 30,462 $ 31,183 $ 27,523 $ 26,181 $ 23,425 $ 21,733 $ 20,551 $ 19,264 $ 18,176 $ 17,984 $ 251 699 2010 — $ 26,077 $ 27,063 $ 25,175 $ 23,307 $ 19,315 $ 17,439 $ 16,047 $ 16,878 18,611 $ 402 498 2011 — — $ 17,249 $ 20,930 $ 19,166 $ 15,836 $ 13,794 $ 12,487 $ 12,358 8,202 $ 500 521 2012 — — — $ 11,162 $ 9,989 $ 8,906 $ 7,441 $ 5,824 $ 4,797 5,051 $ 732 220 2013 — — — — $ 9,807 $ 9,955 $ 9,536 $ 7,226 $ 4,697 3,566 $ 380 218 2014 — — — — — $ 9,989 $ 10,306 $ 9,012 $ 8,984 7,679 $ 2,544 272 2015 — — — — — — $ 9,376 $ 8,757 $ 7,193 5,929 $ 2,770 155 2016 — — — — — — — $ 9,200 $ 8,467 7,413 $ 3,482 180 2017 — — — — — — — — $ 11,049 10,143 $ 7,834 95 2018 — — — — — — — — — 10,141 $ 9,818 188 Total $ 94,719 * Includes expected development on reported claims Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (In thousands) Year Ended December 31, 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 Accident Year Unaudited 2009 $ 116 $ 5,071 $ 7,742 $ 14,675 $ 14,933 $ 15,097 $ 15,184 $ 15,186 $ 16,515 $ 17,522 2010 — $ 485 $ 3,557 $ 8,491 $ 12,283 $ 11,725 $ 12,146 $ 12,253 $ 15,366 17,660 2011 — — $ 118 $ 2,034 $ 3,846 $ 5,062 $ 7,376 $ 7,240 $ 7,799 7,664 2012 — — — $ 568 $ 1,520 $ 2,805 $ 3,247 $ 3,366 $ 3,676 3,800 2013 — — — — $ 102 $ 1,029 $ 1,967 $ 2,599 $ 3,092 3,102 2014 — — — — — $ 388 $ 1,527 $ 2,564 $ 3,046 3,724 2015 — — — — — — $ 25 $ 440 $ 1,625 2,097 2016 — — — — — — — $ 53 $ 1,690 2,365 2017 — — — — — — — — $ 56 1,681 2018 — — — — — — — — — 6 Total 59,621 All outstanding liabilities before 2009, net of reinsurance 1,101 Liabilities for losses and loss adjustment expenses, net of reinsurance $ 36,199 Syndicate 1729 Casualty Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2018 ($ in thousands) Year Ended December 31, IBNR (1) Cumulative Number of Reported Claims (2) 2014 2015 2016 2017 2018 Accident Year Unaudited 2014 $ 6,110 $ 5,812 $ 5,610 $ 5,547 $ 5,472 $ 1,086 nm 2015 — $ 14,810 $ 14,510 $ 14,398 14,232 $ 1,984 nm 2016 — — $ 19,535 $ 19,669 19,552 $ 5,098 nm 2017 — — — $ 22,069 21,824 $ 9,960 nm 2018 — — — — 18,688 $ 16,014 nm Total $ 79,768 (1) Includes expected development on reported claims (2) The abbreviation " nm " indicates that the information is not meaningful Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (In thousands) Year Ended December 31, 2014 2015 2016 2017 2018 Accident Year Unaudited 2014 $ 20 $ 474 $ 4,092 $ 4,214 $ 4,320 2015 — $ 724 $ 6,307 $ 10,313 10,947 2016 — — $ 2,495 $ 8,441 12,869 2017 — — — $ 2,611 8,301 2018 — — — — 1,852 Total 38,289 All outstanding liabilities before 2014, net of reinsurance — Liabilities for losses and loss adjustment expenses, net of reinsurance $ 41,479 Syndicate 1729 Property Insurance Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2018 ($ in thousands) Year Ended December 31, IBNR* Cumulative Number of Reported Claims 2014 2015 2016 2017 2018 Accident Year Unaudited 2014 $ 890 $ 1,089 $ 888 $ 864 $ 866 $ (6 ) 118 2015 — $ 5,519 $ 5,917 $ 6,194 6,159 $ 1,128 921 2016 — — $ 11,896 $ 12,984 12,823 $ 12 2,484 2017 — — — $ 15,018 17,634 $ (883 ) 4,240 2018 — — — — 20,636 $ 6,898 3,681 Total $ 58,118 * Includes expected development on reported claims Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (In thousands) Year Ended December 31, 2014 2015 2016 2017 2018 Accident Year Unaudited 2014 $ 267 $ 1,005 $ 836 $ 854 $ 857 2015 — $ 3,165 $ 4,022 $ 4,808 4,869 2016 — — $ 7,751 $ 10,939 12,343 2017 — — — $ 8,221 16,439 2018 — — — — 9,918 Total 44,426 All outstanding liabilities before 2014, net of reinsurance — Liabilities for losses and loss adjustment expenses, net of reinsurance $ 13,692 Syndicate 1729 Property Reinsurance Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2018 ($ in thousands) Year Ended December 31, IBNR (1) Cumulative Number of Reported Claims (2) 2014 2015 2016 2017 2018 Accident Year Unaudited 2014 $ 831 $ 929 $ 989 $ 989 $ 1,125 $ — nm 2015 $ 2,788 $ 2,825 $ 2,275 2,328 $ (91 ) nm 2016 $ 4,497 $ 4,050 3,368 $ 943 nm 2017 $ 6,861 7,832 $ 371 nm 2018 8,840 $ 8,154 nm Total $ 23,493 (1) Includes expected development on reported claims (2) The abbreviation " nm " indicates that the information is not meaningful Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (In thousands) Year Ended December 31, 2014 2015 2016 2017 2018 Accident Year Unaudited 2014 $ 79 $ 917 $ 984 $ 984 $ 1,125 2015 — $ 1,313 $ 1,804 $ 1,996 2,234 2016 — — $ 613 $ 1,667 2,136 2017 — — — $ 4,147 7,300 2018 — — — — 547 Total 13,342 All outstanding liabilities before 2014, net of reinsurance — Liabilities for losses and loss adjustment expenses, net of reinsurance $ 10,151 Healthcare Professional Liability Claims-Made Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2018 ($ in thousands) Year Ended December 31, IBNR* Cumulative Number of Reported Claims 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 Accident Year Unaudited 2009 $ 379,259 $ 370,642 $ 345,714 $ 320,368 $ 284,511 $ 265,478 $ 246,146 $ 230,849 $ 224,768 $ 220,703 $ (455 ) 3,828 2010 — $ 364,996 $ 354,787 $ 338,170 $ 312,813 $ 291,553 $ 279,713 $ 270,484 $ 258,466 257,714 $ (243 ) 3,847 2011 — — $ 348,916 $ 344,808 $ 331,884 $ 305,540 $ 289,400 $ 278,258 $ 264,777 254,329 $ (2,091 ) 3,532 2012 — — — $ 341,289 $ 324,418 $ 319,613 $ 306,956 $ 291,075 $ 279,589 271,110 $ 276 3,702 2013 — — — — $ 315,346 $ 304,209 $ 296,550 $ 287,140 $ 272,364 258,251 $ 173 3,783 2014 — — — — — $ 290,020 $ 289,397 $ 280,043 $ 267,442 256,968 $ (5,200 ) 3,320 2015 — — — — — — $ 276,492 $ 269,980 $ 271,138 270,814 $ (8,030 ) 3,266 2016 — — — — — — — $ 271,765 $ 274,643 287,551 $ (21,456 ) 3,481 2017 — — — — — — — — $ 283,746 295,883 $ (11,228 ) 3,677 2018 — — — — — — — — — 320,772 $ 129,334 3,558 Total $ 2,694,095 * Includes expected development on reported claims Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (In thousands) Year Ended December 31, 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 Accident Year Unaudited 2009 $ 15,051 $ 71,272 $ 114,318 $ 153,563 $ 178,445 $ 191,420 $ 200,425 $ 205,372 $ 209,016 $ 213,568 2010 — $ 15,464 $ 69,551 $ 137,712 $ 180,432 $ 209,777 $ 221,693 $ 236,171 $ 240,945 243,675 2011 — — $ 14,417 $ 71,208 $ 133,004 $ 177,089 $ 198,112 $ 214,502 $ 224,982 233,103 2012 — — — $ 15,382 $ 73,571 $ 145,488 $ 190,997 $ 215,220 $ 231,652 244,512 2013 — — — — $ 16,938 $ 69,657 $ 127,496 $ 171,681 $ 197,265 213,879 2014 — — — — — $ 16,764 $ 59,485 $ 116,791 $ 154,236 186,239 2015 — — — — — — $ 9,172 $ 55,731 $ 111,741 161,896 2016 — — — — — — — $ 9,027 $ 51,869 109,756 2017 — — — — — — — — $ 16,309 63,171 2018 — — — — — — — — — 14,051 Total 1,683,850 All outstanding liabilities before 2009, net of reinsurance 11,724 Liabilities for losses and loss adjustment expenses, net of reinsurance $ 1,021,969 Healthcare Professional Liability Occurrence Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2018 ($ in thousands) Year Ended December 31, IBNR* Cumulative Number of Reported Claims 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 Accident Year Unaudited 2009 $ 34,450 $ 35,366 $ 36,802 $ 37,437 $ 34,099 $ 32,675 $ 28,731 $ 26,340 $ 24,572 $ 23,387 $ 1,519 246 2010 — $ 41,721 $ 43,238 $ 43,195 $ 42,233 $ 37,920 $ 35,831 $ 33,361 $ 29,338 26,501 $ 946 290 2011 — — $ 45,882 $ 44,956 $ 41,453 $ 39,917 $ 37,150 $ 35,004 $ 32,343 29,784 $ 2,136 342 2012 — — — $ 45,703 $ 46,513 $ 44,848 $ 40,692 $ 34,774 $ 32,691 29,857 $ 3,816 399 2013 — — — — $ 32,746 $ 36,602 $ 35,624 $ 34,393 $ 30,906 26,919 $ 971 356 2014 — — — — — $ 30,420 $ 29,918 $ 32,143 $ 29,869 25,885 $ 2,778 355 2015 — — — — — — $ 35,648 $ 35,347 $ 37,346 40,960 $ 4,667 355 2016 — — — — — — — $ 29,609 $ 28,790 27,240 $ 6,244 322 2017 — — — — — — — — $ 24,571 23,760 $ 19,890 270 2018 — — — — — — — — — 38,420 $ 36,196 118 Total $ 292,713 * Includes expected development on reported claims Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (In thousands) Year Ended December 31, 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 Accident Year Unaudited 2009 $ 175 $ 2,255 $ 5,067 $ 7,947 $ 10,823 $ 13,248 $ 15,380 $ 16,025 $ 16,270 $ 17,022 2010 — $ 285 $ 1,881 $ 5,647 $ 9,120 $ 15,147 $ 21,837 $ 22,804 $ 23,313 23,832 2011 — — $ 291 $ 2,803 $ 8,059 $ 16,544 $ 19,197 $ 21,416 $ 23,194 24,539 2012 — — — $ 363 $ 2,430 $ 7,705 $ 12,212 $ 19,275 $ 21,435 23,095 2013 — — — — $ 369 $ 3,170 $ 7,826 $ 14,753 $ 16,787 18,949 2014 — — — — — $ 394 $ 2,260 $ 7,460 $ 10,519 14,604 2015 — — — — — — $ (350 ) $ 786 $ 4,854 11,626 2016 — — — — — — — $ (182 ) $ (195 ) 2,883 2017 — — — — — — — — $ (6,809 ) (5,858 ) 2018 — — — — — — — — — 65 Total 130,757 All outstanding liabilities before 2009, net of reinsurance 7,985 Liabilities for losses and loss adjustment expenses, net of reinsurance $ 169,941 Workers' Compensation Insurance Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2018 ($ in thousands) Year Ended December 31, IBNR* Cumulative Number of Reported Claims 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 Accident Year Unaudited 2009 $ 45,354 $ 45,354 $ 45,354 $ 45,354 $ 47,811 $ 48,372 $ 47,905 $ 47,480 $ 47,480 $ 47,480 $ 80 10,129 2010 — $ 55,852 $ 55,852 $ 55,852 $ 54,837 $ 54,779 $ 55,200 $ 54,600 $ 54,600 54,600 $ 58 12,913 2011 — — $ 65,665 $ 65,783 $ 71,521 $ 72,280 $ 72,420 $ 72,495 $ 72,795 72,795 $ 354 15,244 2012 — — — $ 80,285 $ 76,551 $ 75,848 $ 76,357 $ 75,836 $ 75,636 75,136 $ 724 16,204 2013 — — — — $ 86,973 $ 85,935 $ 86,928 $ 88,010 $ 88,810 88,810 $ 1,017 16,429 2014 — — — — — $ 93,019 $ 93,529 $ 93,029 $ 92,229 92,229 $ 3,350 16,210 2015 — — — — — — $ 100,101 $ 100,454 $ 98,454 97,654 $ 8,522 16,548 2016 — — — — — — — $ 101,348 $ 97,348 92,148 $ 13,540 15,972 2017 — — — — — — — — $ 99,874 99,874 $ 12,489 16,058 2018 — — — — — — — — — 118,095 $ 32,816 17,556 Total $ 838,821 * Includes expected development on reported claims Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (In thousands) Year Ended December 31, 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 Accident Year Unaudited 2009 $ 14,701 $ 31,465 $ 39,351 $ 43,436 $ 45,689 $ 46,321 $ 46,928 $ 47,012 $ 47,089 $ 47,189 2010 — $ 20,086 $ 39,098 $ 46,762 $ 51,117 $ 52,530 $ 53,443 $ 53,734 $ 53,974 54,014 2011 — — $ 21,993 $ 50,900 $ 62,307 $ 67,945 $ 70,146 $ 70,934 $ 71,662 71,856 2012 — — — $ 27,448 $ 56,122 $ 65,908 $ 70,558 $ 72,766 $ 73,662 73,676 2013 — — — — $ 30,554 $ 63,825 $ 76,813 $ 82,369 $ 85,689 86,783 2014 — — — — — $ 30,368 $ 65,922 $ 77,631 $ 85,022 87,314 2015 — — — — — — $ 32,078 $ 65,070 $ 78,947 83,483 2016 — — — — — — — $ 28,377 $ 58,192 69,237 2017 — — — — — — — — $ 31,586 70,333 2018 — — — — — — — — — 41,619 Total 685,504 All outstanding liabilities before 2009, net of reinsurance 2,208 Liabilities for losses and loss adjustment expenses, net of reinsurance $ 155,525
Schedule of historical claims duration	Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance Years 1 2 3 4 5 6 7 8 9 10 Unaudited Workers' Compensation Insurance 33.2 % 36.5 % 14.1 % 7.1 % 3.3 % 1.3 % 0.7 % 0.3 % 0.1 % 0.2 % Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance Years 1 2 3 4 5 6 7 8 9 10 Unaudited Healthcare Professional Liability Claims-Made 5.4% 19.5% 22.8% 17.0% 10.4% 5.9% 4.6% 2.4% 1.4% 2.1% Healthcare Professional Liability Occurrence (2.3%) 6.1% 15.0% 17.6% 15.2% 11.7% 6.1% 3.1% 1.5% 3.2% Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance Years 1 2 3 4 5 6 7 8 9 10 Unaudited Syndicate 1729 Casualty 18.7 % 40.3 % 22.6 % 12.8 % 3.2 % 1.1 % 1.0 % 0.4 % — % — % Syndicate 1729 Property Insurance 81.4 % 15.9 % 2.1 % 0.2 % 0.2 % 0.1 % 0.1 % 0.1 % — % — % Syndicate 1729 Property Reinsurance 82.0 % 13.3 % 2.8 % 1.1 % 0.4 % 0.2 % 0.1 % — % — % — % Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance Years 1 2 3 4 5 6 7 8 9 10 Unaudited Medical Technology Liability 2.6 % 19.1 % 19.7 % 16.4 % 8.6 % 1.6 % 2.6 % 5.0 % 9.9 % 5.6 % Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance Years 1 2 3 4 5 6 7 8 9 10 Unaudited Segregated Portfolio Cell Reinsurance - Workers' Compensation 34.5 % 38.5 % 14.3 % 4.6 % 1.7 % 0.6 % 0.2 % 0.1 % 0.2 % — %
Schedule of reconciliation of claims development to liability	Below is a reconciliation of the claims development information to the Consolidated Balance Sheet: (In thousands) December 31, 2018 Net outstanding liabilities Healthcare professional liability claims-made $ 1,021,969 Healthcare professional liability occurrence 169,941 Medical technology liability claims-made 36,199 Workers' compensation insurance 155,525 Segregated portfolio cell reinsurance - workers' compensation 56,517 Syndicate 1729 casualty 41,479 Syndicate 1729 property insurance 13,692 Syndicate 1729 property reinsurance 10,151 Other short-duration lines 91,365 Liabilities for losses and loss adjustment expenses, net of reinsurance 1,596,838 Reinsurance recoverable on unpaid losses Healthcare professional liability claims-made 151,870 Healthcare professional liability occurrence 37,683 Medical technology liability claims-made 32,604 Workers' compensation insurance 67,631 Segregated portfolio cell reinsurance - workers' compensation 24,177 Syndicate 1729 casualty 678 Syndicate 1729 property insurance 10,323 Syndicate 1729 property reinsurance 9,717 Other short-duration lines 9,137 Total reinsurance recoverable on unpaid losses and loss adjustment expenses 343,820 Reserve for the future utilization of the DDR benefit 67,200 Unallocated loss adjustment expenses 100,123 Loss portfolio transfer* 18,252 Purchase accounting 1,551 Other (7,937 ) 179,189 Gross liability for losses and loss adjustment expenses $ 2,119,847 * Represents the reserve for retroactive coverage, net of a deferred gain, related to a loss portfolio transfer entered into in the second quarter of 2018 (see Note 4).

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Schedule of future minimum lease payments for operating leases	The following is a schedule of future minimum lease payments for operating leases that had initial or remaining non-cancelable lease terms in excess of one year as of December 31, 2018 . Operating Leases (In thousands) 2019 $ 4,829 2020 4,020 2021 3,557 2022 2,618 2023 1,888 Thereafter 10,212 Total minimum lease payments $ 27,124

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Outstanding long-term debt	ProAssurance’s outstanding debt consisted of the following: (In thousands) December 31, 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%. 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% (4.10% and 2.86%, respectively) determined on a quarterly basis. 39,064 40,460 Total principal 289,064 413,460 Less debt issuance costs 1,307 1,649 Debt less debt issuance costs $ 287,757 $ 411,811
Schedule of debt maturities	At December 31, 2018 , contractual maturities of the Mortgages Loans for each of the next five years, excluding interest payments, are as follows: (In thousands) Principal Payments Due by Period 2019 $ 1,448 2020 1,503 2021 1,559 2022 1,617 2023 1,677 Thereafter 31,260 Total principal payments $ 39,064

Derivatives (Tables)

Derivatives (Tables)	12 Months Ended
	Dec. 31, 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 Consolidated Balance Sheets as of December 31, 2018 and 2017 . ($ in thousands) December 31, 2018 December 31, 2017 Derivatives Not Designated as Hedging Instruments Location in the 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 $ 1,884 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 Consolidated Statements of Income and Comprehensive Income for the years ended December 31, 2018 , 2017 and 2016 . Gains (Losses) Recognized in Income on Derivatives (In thousands) Year Ended December 31 Derivatives Not Designated as Hedging Instruments Location in the Consolidated Statements of Income and Comprehensive Income 2018 2017 2016 Interest Rate Cap Interest expense $ 153 $ (339 ) $ —

Shareholders' Equity (Tables)

Shareholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Schedule of common stock outstanding	The following is a summary of changes in common shares issued and outstanding during the years ended December 31, 2018 , 2017 and 2016 : (In thousands) 2018 2017 2016 Issued and outstanding shares - January 1 53,457 53,251 53,101 Repurchase of shares, at cost of $2 million for 2016 — — (44 ) Shares issued due to exercise of options and vesting of share-based compensation awards 135 132 108 Other shares issued for compensation and shares reissued to stock purchase plan * 45 74 86 Issued and outstanding shares - December 31 53,637 53,457 53,251 * Shares issued were valued at fair value (the market price of a ProAssurance common share on the date of issue).
Schedule of dividends declared	ProAssurance declared cash dividends during 2018 , 2017 and 2016 as follows: Cash Dividends Declared, per Share 2018 2017 2016 First Quarter $ 0.31 $ 0.31 $ 0.31 Second Quarter $ 0.31 $ 0.31 $ 0.31 Third Quarter $ 0.31 $ 0.31 $ 0.31 Fourth Quarter* $ 0.81 $ 5.00 $ 5.00 * Includes special dividends of $0.50 per share in 2018 and $4.69 per share in both 2017 and 2016 .
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: (In thousands) 2018 2017 2016 Reclassifications from AOCI to net income: Realized investment gains (losses) $ 274 $ 2,512 $ 2,417 Non-credit impairment losses reclassified to earnings, due to sale of securities or reclassification as a credit loss (621 ) (3 ) (3,641 ) Unrecognized losses in defined benefit plan liabilities reclassified to earnings, due to the termination and settlement of the plan — — (1,500 ) Total gains (losses) reclassified, before-tax effect (347 ) 2,509 (2,724 ) Tax effect* 73 (878 ) 953 Net reclassification adjustments $ (274 ) $ 1,631 $ (1,771 ) Deferred tax expense (benefit) included in OCI $ (9,573 ) $ (4,676 ) $ (3,078 ) * Tax effects were computed using a 21% for the year ended December 31, 2018 and a 35% rate for the years ended December 31, 2017 and 2016.

Share-Based Payments (Tables)

Share-Based Payments (Tables)	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of compensation expense and related tax benefit recognized during each period, and compensation cost expense in future periods	The following table provides a summary of compensation expense and the total related tax benefit recognized during each period as well as estimated compensation cost that will be charged to expense in future periods. Share-Based Unrecognized Compensation Cost Year Ended December 31 December 31, 2018 ($ in millions, except remaining recognition period) 2018 2017 2016 Amount Weighted Average Remaining Total share-based compensation expense $ 5.3 $ 10.6 $ 12.5 $ 5.9 1.5 Tax benefit recognized $ 1.1 $ 3.7 $ 4.4
Summary of activity related to management share awards	Activity for restricted share units during 2018 , 2017 and 2016 is summarized below. Grant date fair values are based on the market value of a ProAssurance common share on the date of grant less the estimated net present value of dividends during the vesting period. 2018 2017 2016 Units Weighted Units Weighted Units Weighted Beginning non-vested balance 269,520 $ 48.63 240,149 $ 44.07 178,468 $ 43.13 Granted 85,797 $ 44.73 84,565 $ 58.35 109,181 $ 45.59 Forfeited (3,878 ) $ 50.07 (4,087 ) $ 52.35 (5,954 ) $ 43.99 Vested and released (84,116 ) $ 42.90 (51,107 ) $ 43.01 (41,546 ) $ 44.04 Ending non-vested balance 267,323 $ 49.16 269,520 $ 48.63 240,149 $ 44.07
Summary of activity for performance share awards	The table reflects the base number of units; actual awards that vest depend upon the extent to which performance objectives are achieved. Grant date fair values are based on the market value of a ProAssurance common share on the date of grant less the estimated net present value of dividends during the vesting period. 2018 2017 2016 Base Units Weighted Base Units Weighted Base Units Weighted Beginning non-vested balance 212,105 $ 47.11 305,240 $ 43.41 390,350 $ 44.65 Granted 27,202 $ 44.73 48,000 $ 58.35 60,000 $ 45.59 Forfeited — $ — (227 ) $ 42.79 (5,162 ) $ 43.02 Vested and released (104,105 ) $ 42.79 (140,908 ) $ 42.95 (139,948 ) $ 44.05 Ending non-vested balance 135,202 $ 49.95 212,105 $ 47.11 305,240 $ 43.41
Summary of market value of ProAssurance common share on the grant date fair value	Purchase match unit activity during 2018 , 2017 and 2016 is summarized below. Grant date fair values are based on the market value of a ProAssurance common share on the date of grant less the estimated net present value of dividends during the vesting period. 2018 2017 2016 Units Weighted Units Weighted Units Weighted Beginning non-vested balance 70,292 $ 49.40 72,615 $ 45.77 74,483 $ 42.80 Granted — $ — 24,444 $ 51.83 23,903 $ 50.18 Forfeited (1,594 ) $ 50.19 (2,012 ) $ 48.29 (2,875 ) $ 43.77 Vested and released (24,016 ) $ 46.28 (24,755 ) $ 41.33 (22,896 ) $ 40.88 Ending non-vested balance 44,682 $ 51.05 70,292 $ 49.40 72,615 $ 45.77
Summary of fully-vested employee stock options outstanding	ProAssurance also had certain fully-vested employee stock options outstanding during 2016 , as summarized below. ProAssurance had no options exercised during 2018 and 2017 and no outstanding options at December 31, 2018 , 2017 or 2016 . 2018 2017 2016 Options Weighted Options Weighted Options Weighted Outstanding, vested and exercisable, beginning of year — $ — — $ — 2,144 $ 25.02 Exercised — $ — — $ — (2,144 ) $ 25.02 Outstanding, vested and exercisable, end of year — $ — — $ — — $ —

Earnings Per Share (Tables)

Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 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) Year Ended December 31 2018 2017 2016 Weighted average number of common shares outstanding, basic 53,598 53,393 53,216 Dilutive effect of securities: Restricted Share Units 70 85 73 Performance Share Units 63 110 135 Purchase Match Units 18 23 24 Weighted average number of common shares outstanding, diluted 53,749 53,611 53,448 Effect of dilutive shares on earnings per share $ — $ (0.01 ) $ (0.01 )

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Schedule of segment reporting information	Financial results by segment were as follows: Year Ended December 31, 2018 (In thousands) Specialty P&C Workers' Compensation Insurance Segregated Portfolio Cell Reinsurance Lloyd's Syndicates Corporate Inter-segment Eliminations Consolidated Net premiums earned $ 491,787 $ 186,079 73,940 $ 67,047 $ — $ — $ 818,853 Net investment income — — 1,566 3,358 86,960 — 91,884 Equity in earnings (loss) of unconsolidated subsidiaries — — — — 8,948 — 8,948 Net realized gains (losses) — — (3,149 ) (460 ) (39,879 ) — (43,488 ) Other income (expense) (1) 5,844 2,412 211 322 3,525 (2,481 ) 9,833 Net losses and loss adjustment expenses (384,431 ) (118,483 ) (38,726 ) (51,570 ) — — (593,210 ) Underwriting, policy acquisition and operating expenses (1) (112,419 ) (55,693 ) (22,426 ) (31,686 ) (18,767 ) 2,435 (238,556 ) Segregated portfolio cells dividend (expense) income — — (9,122 ) — — — (9,122 ) Interest expense — — — — (16,163 ) 46 (16,117 ) Income tax benefit (expense) — — — 317 17,715 — 18,032 Segment operating results $ 781 $ 14,315 $ 2,294 $ (12,672 ) $ 42,339 $ — $ 47,057 Significant non-cash items: Depreciation and amortization, net of accretion $ 7,050 $ 3,850 $ 441 $ (8 ) $ 9,922 $ — $ 21,255 Year Ended December 31, 2017 (In thousands) Specialty P&C Workers' Compensation Insurance Segregated Portfolio Cell Reinsurance Lloyd's Syndicates Corporate Inter-segment Eliminations Consolidated Net premiums earned $ 449,823 $ 163,309 $ 68,197 $ 57,202 $ — $ — $ 738,531 Net investment income — — 1,059 1,736 92,867 — 95,662 Equity in earnings (loss) of unconsolidated subsidiaries — — — — 8,033 — 8,033 Net realized gains (losses) — — 3,914 107 12,388 — 16,409 Other income (expense) (1) 5,688 2,096 115 (1,476 ) 2,888 (1,797 ) 7,514 Net losses and loss adjustment expenses (285,250 ) (102,233 ) (37,455 ) (44,220 ) — — (469,158 ) Underwriting, policy acquisition and operating expenses (1) (107,972 ) (52,576 ) (20,764 ) (26,963 ) (29,275 ) 1,797 (235,753 ) Segregated portfolio cells dividend (expense) income (2) (5,181 ) — (10,590 ) — — — (15,771 ) Interest expense — — — — (16,844 ) — (16,844 ) Income tax benefit (expense) (2) — — — 568 (21,927 ) — (21,359 ) Segment operating results $ 57,108 $ 10,596 $ 4,476 $ (13,046 ) $ 48,130 $ — $ 107,264 Significant non-cash items: Depreciation and amortization, net of accretion $ 7,922 $ 3,480 $ 680 $ (20 ) $ 16,734 $ — $ 28,796 Year Ended December 31, 2016 (In thousands) Specialty P&C Workers' Compensation Insurance Segregated Portfolio Cell Reinsurance Lloyd's Syndicates Corporate Inter-segment Eliminations Consolidated Net premiums earned $ 454,506 $ 161,988 $ 62,137 $ 54,650 $ — $ — $ 733,281 Net investment income — — 711 1,410 97,891 — 100,012 Equity in earnings (loss) of unconsolidated subsidiaries — — — — (5,762 ) — (5,762 ) Net realized gains (losses) — — 2,525 76 32,274 — 34,875 Other income (expense) (1) 5,306 2,218 18 1,415 1,069 (2,218 ) 7,808 Net losses and loss adjustment expenses (266,090 ) (107,791 ) (35,232 ) (34,116 ) — — (443,229 ) Underwriting, policy acquisition and operating expenses (1) (103,656 ) (53,597 ) (18,936 ) (22,832 ) (30,807 ) 2,218 (227,610 ) Segregated portfolio cells dividend (expense) income — — (8,142 ) — — — (8,142 ) Interest expense — — — — (15,032 ) — (15,032 ) Income tax benefit (expense) — — — (384 ) (24,736 ) — (25,120 ) Segment operating results $ 90,066 $ 2,818 $ 3,081 $ 219 $ 54,897 $ — $ 151,081 Significant non-cash items: Depreciation and amortization, net of accretion $ 7,268 $ 5,600 $ 595 $ 132 $ 19,194 $ — $ 32,789 (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 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 2017 related to periods prior to the then current period and was unrelated to the Company's Cayman Islands captive operations. The $1.8 million tax impact of the expense recognized in 2017 was included in the Corporate segment's income tax benefit (expense).
Schedule of product and service revenue from external customers	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. Year Ended December 31 (In thousands) 2018 2017 2016 Specialty P&C Segment Gross premiums earned: Healthcare professional liability $ 518,303 $ 477,561 $ 474,981 Legal professional liability 26,094 25,771 26,125 Medical technology liability 35,157 33,836 34,158 Other 468 415 667 Ceded premiums earned (88,235 ) (87,760 ) (81,425 ) Segment net premiums earned 491,787 449,823 454,506 Workers' Compensation Insurance Segment Gross premiums earned: Traditional business 199,466 173,246 171,434 Alternative market business 83,508 80,698 75,658 Ceded premiums earned (96,895 ) (90,635 ) (85,104 ) Segment net premiums earned 186,079 163,309 161,988 Segregated Portfolio Cell Reinsurance Segment Gross premiums earned: Workers' compensation (1) 78,255 72,814 66,899 Healthcare professional liability (2) 5,009 4,097 3,310 Ceded premiums earned (9,324 ) (8,714 ) (8,072 ) Segment net premiums earned 73,940 68,197 62,137 Lloyd's Syndicates Segment Gross premiums earned: Property and casualty (3) 83,307 69,749 60,564 Ceded premiums earned (16,260 ) (12,547 ) (5,914 ) Segment net premiums earned 67,047 57,202 54,650 Consolidated net premiums earned $ 818,853 $ 738,531 $ 733,281 (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 $5.0 million , $11.8 million and $14.0 million for years ended December 31, 2018 , 2017 and 2016 , respectively.

Statutory Accounting and Divi_2

Statutory Accounting and Dividend Restrictions (Tables)	12 Months Ended
	Dec. 31, 2018
Insurance [Abstract]
Consolidated net income	Net earnings and capital and surplus of ProAssurance’s insurance subsidiaries on a statutory basis are shown in the following table. (In millions) Statutory Net Earnings Statutory Capital and Surplus 2018 2017 2016 2018 2017 $135 $139 $163 $1,041 $1,175

Quarterly Results of Operatio_2

Quarterly Results of Operations (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Data [Abstract]
Summary of unaudited quarterly results of operations	The following is a summary of unaudited quarterly results of operations for 2018 and 2017 : 2018* (In thousands, except per share data) 1st 2nd 3rd 4th Net premiums earned $ 187,159 $ 223,591 $ 206,070 $ 202,033 Net losses and loss adjustment expenses: Current year $ 152,572 $ 184,543 $ 169,154 $ 179,056 Favorable development of reserves established in prior years, net $ (22,786 ) $ (22,815 ) $ (21,549 ) $ (24,967 ) Net income (loss) $ 11,856 $ 28,423 $ 31,228 $ (24,450 ) Basic earnings per share $ 0.22 $ 0.53 $ 0.58 $ (0.46 ) Diluted earnings per share $ 0.22 $ 0.53 $ 0.58 $ (0.46 ) 2017* (In thousands, except per share data) 1st 2nd 3rd 4th Net premiums earned $ 182,903 $ 180,353 $ 192,303 $ 182,972 Net losses and loss adjustment expenses: Current year $ 147,927 $ 144,562 $ 161,631 $ 149,399 Favorable development of reserves established in prior years, net $ (28,776 ) $ (29,012 ) $ (32,275 ) $ (44,297 ) Net income (loss) $ 41,455 $ 19,518 $ 28,949 $ 17,342 Basic earnings per share $ 0.78 $ 0.37 $ 0.54 $ 0.32 Diluted earnings per share $ 0.77 $ 0.36 $ 0.54 $ 0.32 *Due to rounding, the sum of quarterly amounts may not equal the total amount for the respective year-to-date periods

Accounting Policies - Narrative

Accounting Policies - Narrative (Details)	12 Months Ended
	Dec. 31, 2018USD ($)reporting_unitsegment	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Jan. 01, 2019USD ($)
Accounting Policies [Abstract]
Number of reportable segments | segment	5
Insurance policy duration (years)	1 year
Recorded allowances for credit losses (less than)	$ 1,500,000	$ 1,500,000
Estimated credit losses (more than)	500,000	500,000
Earned but unbilled premiums	$ 4,300,000	4,300,000
Minimum period for claims resolution (years)	5 years
Number of of reporting units (in reporting units) | reporting_unit	5
Number of reporting units with goodwill (in reporting units) | reporting_unit	3
Goodwill impairment loss	$ 0	0	$ 0
Property, Plant and Equipment [Line Items]
Return of invested capital from unconsolidated subsidiaries	84,534,000	32,539,000	7,084,000
Equity securities, FV-NI, gain (loss)	12,800,000
Net investment income	91,884,000	95,662,000	100,012,000
Building and Building Improvements
Property, Plant and Equipment [Line Items]
Real estate accumulated depreciation	25,200,000	24,000,000
Real estate depreciation expense	1,200,000	1,100,000	1,400,000
Retained Earnings
Property, Plant and Equipment [Line Items]
Tax Cuts and Jobs Act of 2017, reclassification	(3,400,000)
AOCI Attributable to Parent
Property, Plant and Equipment [Line Items]
Tax Cuts and Jobs Act of 2017, reclassification	3,400,000
Accounting Standards Update 2016-15
Property, Plant and Equipment [Line Items]
Return of invested capital from unconsolidated subsidiaries		24,400,000	$ 9,900,000
Accounting Standards Update 2016-01
Property, Plant and Equipment [Line Items]
Cumulative-effect adjustment ASU adoption		8,334,000
Net investment income	$ 22,000,000
Accounting Standards Update 2016-01 | Retained Earnings
Property, Plant and Equipment [Line Items]
Cumulative-effect adjustment ASU adoption		$ 8,334,000
Forecast | Accounting Standards Update 2016-02
Property, Plant and Equipment [Line Items]
Right-of-use asset				$ 19,000,000
Lease liability				$ 19,000,000

Accounting Policies - Intangibl

Accounting Policies - Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Gross carrying value non-amortizable	$ 25.8	$ 25.8
Gross carrying value amortizable	97.5	97.5
Accumulated amortization of intangible assets	46.5	40.3
Amortization expense of intangible assets	6.2	5.8	$ 8.1
Total Intangible Assets	123.3	$ 123.3
Estimated aggregate amortization of intangible assets, next 12 months	6.1
Estimated aggregate amortization of intangible assets for 2020	6.1
Estimated aggregate amortization of intangible assets for 2021	6
Estimated aggregate amortization of intangible assets for 2022	6
Estimated aggregate amortization of intangible assets for 2023	$ 6

Accounting Policies - Other Lia

Accounting Policies - Other Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
SPC dividends payable	$ 53,604	$ 46,925
Unpaid dividends	43,446	267,292	$ 265,659
All other	102,245	123,383
Total other liabilities	$ 199,295	$ 437,600

Accounting Policies - Accountin

Accounting Policies - Accounting Changes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Return of invested capital from unconsolidated subsidiaries	$ 84,534	$ 32,539	$ 7,084
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Tax Cuts and Jobs Act of 2017, reclassification	(3,400)
Accumulated Other Comprehensive Income (Loss)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Tax Cuts and Jobs Act of 2017, reclassification	$ 3,400
Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative-effect adjustment ASU adoption		8,334
Accounting Standards Update 2016-01 | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative-effect adjustment ASU adoption		8,334
Accounting Standards Update 2016-15
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Return of invested capital from unconsolidated subsidiaries		$ 24,400	$ 9,900

Fair Value Measurement - Assets

Fair Value Measurement - Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Assets:
Fixed maturities available for sale, at fair value	$ 2,093,798	$ 2,280,242
Equity investments	442,937	470,609
Alternative investment	288,728	230,889
Recurring fair value measurements
Assets:
Fixed maturities, trading	38,188
Other assets	1,884	1,731
Total assets categorized within the fair value hierarchy	2,896,178	3,216,879
Alternative investment	268,436
Total assets at fair value	3,184,906	3,447,768
Recurring fair value measurements | Level 1
Assets:
Fixed maturities, trading	0
Other assets	0	0
Total assets categorized within the fair value hierarchy	690,874	877,791
Recurring fair value measurements | Level 2
Assets:
Fixed maturities, trading	38,188
Other assets	1,884	1,731
Total assets categorized within the fair value hierarchy	2,197,129	2,319,990
Recurring fair value measurements | Level 3
Assets:
Fixed maturities, trading	0
Other assets	0	0
Total assets categorized within the fair value hierarchy	8,175	19,098
U.S. Treasury obligations
Assets:
Fixed maturities available for sale, at fair value	120,201	133,627
U.S. Treasury obligations | Recurring fair value measurements
Assets:
Fixed maturities available for sale, at fair value	120,201	133,627
U.S. Treasury obligations | Recurring fair value measurements | Level 1
Assets:
Fixed maturities available for sale, at fair value	0	0
U.S. Treasury obligations | Recurring fair value measurements | Level 2
Assets:
Fixed maturities available for sale, at fair value	120,201	133,627
U.S. Treasury obligations | Recurring fair value measurements | Level 3
Assets:
Fixed maturities available for sale, at fair value	0	0
U.S. Government-sponsored enterprise obligations
Assets:
Fixed maturities available for sale, at fair value	35,354	20,956
U.S. Government-sponsored enterprise obligations | Recurring fair value measurements
Assets:
Fixed maturities available for sale, at fair value	35,354	20,956
U.S. Government-sponsored enterprise obligations | Recurring fair value measurements | Level 1
Assets:
Fixed maturities available for sale, at fair value	0	0
U.S. Government-sponsored enterprise obligations | Recurring fair value measurements | Level 2
Assets:
Fixed maturities available for sale, at fair value	35,354	20,956
U.S. Government-sponsored enterprise obligations | Recurring fair value measurements | Level 3
Assets:
Fixed maturities available for sale, at fair value	0	0
State and municipal bonds
Assets:
Fixed maturities available for sale, at fair value	293,772	632,243
State and municipal bonds | Recurring fair value measurements
Assets:
Fixed maturities available for sale, at fair value	293,772	632,243
State and municipal bonds | Recurring fair value measurements | Level 1
Assets:
Fixed maturities available for sale, at fair value	0	0
State and municipal bonds | Recurring fair value measurements | Level 2
Assets:
Fixed maturities available for sale, at fair value	293,772	632,243
State and municipal bonds | Recurring fair value measurements | Level 3
Assets:
Fixed maturities available for sale, at fair value	0	0
Corporate debt, multiple observable inputs | Recurring fair value measurements
Assets:
Fixed maturities available for sale, at fair value	1,219,153	1,153,455
Corporate debt, multiple observable inputs | Recurring fair value measurements | Level 1
Assets:
Fixed maturities available for sale, at fair value	2,319	2,371
Corporate debt, multiple observable inputs | Recurring fair value measurements | Level 2
Assets:
Fixed maturities available for sale, at fair value	1,216,834	1,151,084
Corporate debt, multiple observable inputs | Recurring fair value measurements | Level 3
Assets:
Fixed maturities available for sale, at fair value	0	0
Corporate debt, limited observable inputs | Level 3
Assets:
Fixed maturities available for sale, at fair value	4,322	13,703
Corporate debt, limited observable inputs | Recurring fair value measurements
Assets:
Fixed maturities available for sale, at fair value	4,322	13,703
Corporate debt, limited observable inputs | Recurring fair value measurements | Level 1
Assets:
Fixed maturities available for sale, at fair value	0	0
Corporate debt, limited observable inputs | Recurring fair value measurements | Level 2
Assets:
Fixed maturities available for sale, at fair value	0	0
Corporate debt, limited observable inputs | Recurring fair value measurements | Level 3
Assets:
Fixed maturities available for sale, at fair value	4,322	13,703
Residential mortgage-backed securities
Assets:
Fixed maturities available for sale, at fair value	181,238	197,844
Residential mortgage-backed securities | Recurring fair value measurements
Assets:
Fixed maturities available for sale, at fair value	181,238	197,844
Residential mortgage-backed securities | Recurring fair value measurements | Level 1
Assets:
Fixed maturities available for sale, at fair value	0	0
Residential mortgage-backed securities | Recurring fair value measurements | Level 2
Assets:
Fixed maturities available for sale, at fair value	181,238	196,789
Residential mortgage-backed securities | Recurring fair value measurements | Level 3
Assets:
Fixed maturities available for sale, at fair value	0	1,055
Agency commercial mortgage-backed securities
Assets:
Fixed maturities available for sale, at fair value	13,108	10,742
Agency commercial mortgage-backed securities | Recurring fair value measurements
Assets:
Fixed maturities available for sale, at fair value	13,108	10,742
Agency commercial mortgage-backed securities | Recurring fair value measurements | Level 1
Assets:
Fixed maturities available for sale, at fair value	0	0
Agency commercial mortgage-backed securities | Recurring fair value measurements | Level 2
Assets:
Fixed maturities available for sale, at fair value	13,108	10,742
Agency commercial mortgage-backed securities | Recurring fair value measurements | Level 3
Assets:
Fixed maturities available for sale, at fair value	0	0
Other commercial mortgage-backed securities
Assets:
Fixed maturities available for sale, at fair value	30,993	15,961
Other commercial mortgage-backed securities | Recurring fair value measurements
Assets:
Fixed maturities available for sale, at fair value	30,993	15,961
Other commercial mortgage-backed securities | Recurring fair value measurements | Level 1
Assets:
Fixed maturities available for sale, at fair value	0	0
Other commercial mortgage-backed securities | Recurring fair value measurements | Level 2
Assets:
Fixed maturities available for sale, at fair value	30,993	15,961
Other commercial mortgage-backed securities | Recurring fair value measurements | Level 3
Assets:
Fixed maturities available for sale, at fair value	0	0
Other asset-backed securities
Assets:
Fixed maturities available for sale, at fair value	195,657	101,711
Other asset-backed securities | Recurring fair value measurements
Assets:
Fixed maturities available for sale, at fair value	195,657	101,711
Other asset-backed securities | Recurring fair value measurements | Level 1
Assets:
Fixed maturities available for sale, at fair value	0	0
Other asset-backed securities | Recurring fair value measurements | Level 2
Assets:
Fixed maturities available for sale, at fair value	191,807	97,780
Other asset-backed securities | Recurring fair value measurements | Level 3
Assets:
Fixed maturities available for sale, at fair value	3,850	3,931
Financial | Recurring fair value measurements
Assets:
Equity investments	62,344	76,051
Financial | Recurring fair value measurements | Level 1
Assets:
Equity investments	62,344	76,051
Financial | Recurring fair value measurements | Level 2
Assets:
Equity investments	0	0
Financial | Recurring fair value measurements | Level 3
Assets:
Equity investments	0	0
Utilities/Energy | Recurring fair value measurements
Assets:
Equity investments	46,533	54,388
Utilities/Energy | Recurring fair value measurements | Level 1
Assets:
Equity investments	46,533	54,388
Utilities/Energy | Recurring fair value measurements | Level 2
Assets:
Equity investments	0	0
Utilities/Energy | Recurring fair value measurements | Level 3
Assets:
Equity investments	0	0
Consumer oriented | Recurring fair value measurements
Assets:
Equity investments	47,462	54,529
Consumer oriented | Recurring fair value measurements | Level 1
Assets:
Equity investments	47,462	54,529
Consumer oriented | Recurring fair value measurements | Level 2
Assets:
Equity investments	0	0
Consumer oriented | Recurring fair value measurements | Level 3
Assets:
Equity investments	0	0
Industrial | Recurring fair value measurements
Assets:
Equity investments	41,487	53,936
Industrial | Recurring fair value measurements | Level 1
Assets:
Equity investments	41,487	53,936
Industrial | Recurring fair value measurements | Level 2
Assets:
Equity investments	0	0
Industrial | Recurring fair value measurements | Level 3
Assets:
Equity investments	0	0
Bond funds | Recurring fair value measurements
Assets:
Equity investments	174,753	156,563
Bond funds | Recurring fair value measurements | Level 1
Assets:
Equity investments	174,753	156,563
Bond funds | Recurring fair value measurements | Level 2
Assets:
Equity investments	0	0
Bond funds | Recurring fair value measurements | Level 3
Assets:
Equity investments	0	0
All other | Recurring fair value measurements
Assets:
Equity investments	50,066	75,142
All other | Recurring fair value measurements | Level 1
Assets:
Equity investments	50,066	75,142
All other | Recurring fair value measurements | Level 2
Assets:
Equity investments	0	0
All other | Recurring fair value measurements | Level 3
Assets:
Equity investments	0	0
Short-term investments | Recurring fair value measurements
Assets:
Short-term investments	308,319	432,126
Short-term investments | Recurring fair value measurements | Level 1
Assets:
Short-term investments	265,910	404,204
Short-term investments | Recurring fair value measurements | Level 2
Assets:
Short-term investments	42,409	27,922
Short-term investments | Recurring fair value measurements | Level 3
Assets:
Short-term investments	0	0
Other investments | Level 3
Assets:
Total assets categorized within the fair value hierarchy	3	409
Other investments | Recurring fair value measurements
Assets:
Short-term investments	31,344	32,171
Alternative investment		20,130
Other investments | Recurring fair value measurements | Level 1
Assets:
Short-term investments	0	607
Other investments | Recurring fair value measurements | Level 2
Assets:
Short-term investments	31,341	31,155
Other investments | Recurring fair value measurements | Level 3
Assets:
Short-term investments	3	409
Equity Securities | Recurring fair value measurements
Assets:
Alternative investment	20,292
Investment in unconsolidated subsidiaries
Assets:
Alternative investment	$ 268,436	210,759
Investment in unconsolidated subsidiaries | Recurring fair value measurements
Assets:
Alternative investment		$ 210,759

Fair Value Measurement - Narrat

Fair Value Measurement - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)Agreement	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
OTTI loss, debt securities, portion recognized in earnings	$ 490	$ 12,952	$ 9,766
Deferred compensation plan assets	$ 24,100	$ 20,200
Number of line of credit agreements | Agreement	2
Corporate debt, limited observable inputs | Nationally Recognized Statistical Rating Organization (NRSRO) | Rating BBBplus
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Credit rating	54.00%	84.00%
Residential mortgage-backed and other asset-backed securities | Nationally Recognized Statistical Rating Organization (NRSRO) | Rating AAA
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Credit rating	25.00%	21.00%
Investment in unconsolidated subsidiaries | Early Stage Business Development
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
OTTI loss, debt securities, portion recognized in earnings		$ 8,500
Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net asset (liability) fair value		$ 1,200

Fair Value Measurement - Quanti

Fair Value Measurement - Quantitative Information Regarding Level 3 Valuations (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Assets:
Fixed maturities available for sale, at fair value	$ 2,093,798	$ 2,280,242
Fair Value, Inputs, Level 3 | Corporate debt, limited observable inputs
Assets:
Fixed maturities available for sale, at fair value	$ 4,322	13,703
Fair Value, Inputs, Level 3 | Corporate debt, limited observable inputs | Market Comparable Securities | Comparability Adjustment | Minimum
Assets:
Available-for-sale, measurement input	0
Fair Value, Inputs, Level 3 | Corporate debt, limited observable inputs | Market Comparable Securities | Comparability Adjustment | Maximum
Assets:
Available-for-sale, measurement input	0.05
Fair Value, Inputs, Level 3 | Corporate debt, limited observable inputs | Market Comparable Securities | Comparability Adjustment | Weighted Average
Assets:
Available-for-sale, measurement input	0.025
Fair Value, Inputs, Level 3 | Corporate debt, limited observable inputs | Discounted Cash Flows | Comparability Adjustment | Minimum
Assets:
Available-for-sale, measurement input	0
Fair Value, Inputs, Level 3 | Corporate debt, limited observable inputs | Discounted Cash Flows | Comparability Adjustment | Maximum
Assets:
Available-for-sale, measurement input	0.05
Fair Value, Inputs, Level 3 | Corporate debt, limited observable inputs | Discounted Cash Flows | Comparability Adjustment | Weighted Average
Assets:
Available-for-sale, measurement input	0.025
Fair Value, Inputs, Level 3 | Residential mortgage-backed and other asset-backed securities
Assets:
Fixed maturities available for sale, at fair value	$ 3,850	4,986
Fair Value, Inputs, Level 3 | Residential mortgage-backed and other asset-backed securities | Market Comparable Securities | Comparability Adjustment | Minimum
Assets:
Available-for-sale, measurement input	0
Fair Value, Inputs, Level 3 | Residential mortgage-backed and other asset-backed securities | Market Comparable Securities | Comparability Adjustment | Maximum
Assets:
Available-for-sale, measurement input	0.05
Fair Value, Inputs, Level 3 | Residential mortgage-backed and other asset-backed securities | Market Comparable Securities | Comparability Adjustment | Weighted Average
Assets:
Available-for-sale, measurement input	0.025
Fair Value, Inputs, Level 3 | Residential mortgage-backed and other asset-backed securities | Discounted Cash Flows | Comparability Adjustment | Minimum
Assets:
Available-for-sale, measurement input	0
Fair Value, Inputs, Level 3 | Residential mortgage-backed and other asset-backed securities | Discounted Cash Flows | Comparability Adjustment | Maximum
Assets:
Available-for-sale, measurement input	0.05
Fair Value, Inputs, Level 3 | Residential mortgage-backed and other asset-backed securities | Discounted Cash Flows | Comparability Adjustment | Weighted Average
Assets:
Available-for-sale, measurement input	0.025
Fair Value, Inputs, Level 3 | Other investments
Assets:
Fair value	$ 3	$ 409
Fair Value, Inputs, Level 3 | Other investments | Discounted Cash Flows | Comparability Adjustment | Minimum
Assets:
Other investments, measurement input	0.00%
Fair Value, Inputs, Level 3 | Other investments | Discounted Cash Flows | Comparability Adjustment | Maximum
Assets:
Other investments, measurement input	10.00%
Fair Value, Inputs, Level 3 | Other investments | Discounted Cash Flows | Comparability Adjustment | Weighted Average
Assets:
Other investments, measurement input	5.00%

Fair Value Measurement - Level

Fair Value Measurement - Level 3 Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation:
Beginning Balance	$ 19,098	$ 17,820
Total gains (losses) realized and unrealized:
Included in other comprehensive income	(338)	(300)
Purchases	28,098	15,643
Sales	(7,210)	(5,749)
Transfers in	2,627	2,320
Transfers out	(33,906)	(10,343)
Ending Balance	8,175	19,098
Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end	0	0
Net investment income
Total gains (losses) realized and unrealized:
Included in earnings	(146)	(163)
Net realized investment gains (losses)
Total gains (losses) realized and unrealized:
Included in earnings	(48)	(130)
Corporate debt
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation:
Beginning Balance	13,703	14,810
Total gains (losses) realized and unrealized:
Included in other comprehensive income	(233)	(369)
Purchases	8,005	13,016
Sales	(6,406)	(4,837)
Transfers in	2,627	999
Transfers out	(13,218)	(9,766)
Ending Balance	4,322	13,703
Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end	0	0
Corporate debt | Net investment income
Total gains (losses) realized and unrealized:
Included in earnings	(148)	(163)
Corporate debt | Net realized investment gains (losses)
Total gains (losses) realized and unrealized:
Included in earnings	(8)	13
Asset-backed Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation:
Beginning Balance	4,986	3,007
Total gains (losses) realized and unrealized:
Included in other comprehensive income	(105)	(71)
Purchases	20,093	2,627
Sales	(438)	0
Transfers in	0	0
Transfers out	(20,688)	(577)
Ending Balance	3,850	4,986
Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end	0	0
Asset-backed Securities | Net investment income
Total gains (losses) realized and unrealized:
Included in earnings	2	0
Asset-backed Securities | Net realized investment gains (losses)
Total gains (losses) realized and unrealized:
Included in earnings	0	0
Other investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation:
Beginning Balance	409	3
Total gains (losses) realized and unrealized:
Included in other comprehensive income	0	140
Purchases	0	0
Sales	(366)	(912)
Transfers in	0	1,321
Transfers out	0	0
Ending Balance	3	409
Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end	0	0
Other investments | Net investment income
Total gains (losses) realized and unrealized:
Included in earnings	0	0
Other investments | Net realized investment gains (losses)
Total gains (losses) realized and unrealized:
Included in earnings	$ (40)	$ (143)

Fair Value Measurement - Invest

Fair Value Measurement - Investments in LLCs and Limited Partnerships (Details)	12 Months Ended
	Dec. 31, 2018USD ($)fund	Dec. 31, 2017USD ($)
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Alternative investment	$ 288,728,000	$ 230,889,000
Private debt funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Number of unrelated LPs funds | fund	3
Number of LPs to allow redemption by special consent (in funds) | fund	1
Number of LPs that do not permit redemption (in funds) | fund	2
Private debt funds | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Anticipated time frame for distribution at the discretion of the LP (years)	3 years
Private debt funds | Maximum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Anticipated time frame for distribution at the discretion of the LP (years)	8 years
Long equity fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Entities that calculate net asset value notice period (years)	15 days
Payment period for redemption of LP valued at NAV (years)	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 (years)	30 days
Redemption percentage of LP at NAV for which initial payment is limited (percent)	90.00%
Long/short equity funds | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Entities that calculate net asset value notice period (years)	30 days
Long/short equity funds | Maximum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Entities that calculate net asset value notice period (years)	90 days
Non-public equity funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Anticipated time frame for distribution at the discretion of the LP (years)	9 years
Structured credit fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Prior notice requirement notice for two funds	90 days
Prior notice requirement notice for one funds	180 days
Long/short commodities fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Entities that calculate net asset value notice period (years)	30 days
Lock-up period (in years)	1 year
Payment period for redemption of LP valued at NAV (years)	30 days
Mortgage fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Entities that calculate net asset value notice period (years)	65 days
Payment period for redemption of LP valued at NAV (years)	45 days
Equities | Mortgage fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Commitments	$ 0
Alternative investment	20,292,000	0
Investment in unconsolidated subsidiaries
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Alternative investment	268,436,000	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	20,954,000
Alternative investment	18,196,000	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
Alternative investment	6,561,000	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
Alternative investment	28,805,000	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	80,076,000
Alternative investment	114,811,000	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
Alternative investment	9,322,000	9,100,000
Investment in unconsolidated subsidiaries | Structured credit fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Commitments	8,916,000
Alternative investment	29,164,000	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
Alternative investment	12,958,000	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	24,539,000
Alternative investment	48,619,000	606,000
Other investments | Mortgage fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Alternative investment	$ 0	$ 20,130,000

Fair Value Measurement - Method

Fair Value Measurement - Methodologies Other Than Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Carrying Value
Financial assets:
Other assets	$ 35,921	$ 34,020
Financial liabilities:
Other liabilities	21,300	21,154
Carrying Value | Senior Notes
Financial liabilities:
Debt	250,000	250,000
Carrying Value | Line of Credit
Financial liabilities:
Debt	0	123,000
Carrying Value | Mortgage Loans
Financial liabilities:
Debt	39,064	40,460
Fair Value
Financial assets:
Other assets	35,468	33,742
Financial liabilities:
Other liabilities	21,300	21,154
Fair Value | Senior Notes
Financial liabilities:
Debt	264,810	273,153
Fair Value | Line of Credit
Financial liabilities:
Debt	0	123,000
Fair Value | Mortgage Loans
Financial liabilities:
Debt	39,064	40,460
BOLI | Carrying Value
Financial assets:
Other investments	64,096	62,113
BOLI | Fair Value
Financial assets:
Other investments	64,096	62,113
Other investments | Carrying Value
Financial assets:
Other investments	2,943	58,546
Other investments | Fair Value
Financial assets:
Other investments	$ 2,943	$ 69,095

Investments - Available-For-Sal

Investments - Available-For-Sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 2,116,825	$ 2,257,188
Gross Unrealized Gains	9,679	32,610
Gross Unrealized Losses	32,706	9,556
Fixed maturities available for sale, at fair value	2,093,798	2,280,242
U.S. Treasury obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	121,274	134,323
Gross Unrealized Gains	331	485
Gross Unrealized Losses	1,404	1,181
Fixed maturities available for sale, at fair value	120,201	133,627
U.S. Government-sponsored enterprise obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	35,758	21,089
Gross Unrealized Gains	25	73
Gross Unrealized Losses	429	206
Fixed maturities available for sale, at fair value	35,354	20,956
State and municipal bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	289,544	618,414
Gross Unrealized Gains	4,877	14,248
Gross Unrealized Losses	649	419
Fixed maturities available for sale, at fair value	293,772	632,243
Corporate debt
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,244,577	1,157,660
Gross Unrealized Gains	3,328	15,205
Gross Unrealized Losses	24,430	5,707
Fixed maturities available for sale, at fair value	1,223,475	1,167,158
Residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	184,463	196,741
Gross Unrealized Gains	814	2,438
Gross Unrealized Losses	4,039	1,335
Fixed maturities available for sale, at fair value	181,238	197,844
Agency commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	13,296	10,827
Gross Unrealized Gains	12	23
Gross Unrealized Losses	200	108
Fixed maturities available for sale, at fair value	13,108	10,742
Other commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	31,330	16,004
Gross Unrealized Gains	38	91
Gross Unrealized Losses	375	134
Fixed maturities available for sale, at fair value	30,993	15,961
Other asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	196,583	102,130
Gross Unrealized Gains	254	47
Gross Unrealized Losses	1,180	466
Fixed maturities available for sale, at fair value	$ 195,657	$ 101,711

Investments - Available-For-S_2

Investments - Available-For-Sale Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fixed maturities, available for sale
Amortized Cost	$ 2,116,825	$ 2,257,188
Total Fair Value	2,093,798	2,280,242
U.S. Treasury obligations
Fixed maturities, available for sale
Amortized Cost	121,274	134,323
Due in one year or less	27,187
Due after one year through five years	74,196
Due after five years through ten years	18,416
Due after ten years	402
Total Fair Value	120,201	133,627
U.S. Government-sponsored enterprise obligations
Fixed maturities, available for sale
Amortized Cost	35,758	21,089
Due in one year or less	3,279
Due after one year through five years	12,301
Due after five years through ten years	19,640
Due after ten years	134
Total Fair Value	35,354	20,956
State and municipal bonds
Fixed maturities, available for sale
Amortized Cost	289,544	618,414
Due in one year or less	10,506
Due after one year through five years	126,225
Due after five years through ten years	129,118
Due after ten years	27,923
Total Fair Value	293,772	632,243
Corporate debt
Fixed maturities, available for sale
Amortized Cost	1,244,577	1,157,660
Due in one year or less	147,223
Due after one year through five years	726,570
Due after five years through ten years	324,467
Due after ten years	25,215
Total Fair Value	1,223,475	1,167,158
Residential mortgage-backed securities
Fixed maturities, available for sale
Amortized Cost	184,463	196,741
Total Fair Value	181,238	197,844
Agency commercial mortgage-backed securities
Fixed maturities, available for sale
Amortized Cost	13,296	10,827
Total Fair Value	13,108	10,742
Other commercial mortgage-backed securities
Fixed maturities, available for sale
Amortized Cost	31,330	16,004
Total Fair Value	30,993	15,961
Other asset-backed securities
Fixed maturities, available for sale
Amortized Cost	196,583	102,130
Total Fair Value	$ 195,657	$ 101,711

Investments - Available-For-S_3

Investments - Available-For-Sale Securities Narrative (Details) $ in Millions	Dec. 31, 2018USD ($)Affiliate
Debt Securities, Available-for-sale [Line Items]
Number of investment affiliates exceeding shareholder's equity ten percent threshold limit (in affiliates) | Affiliate	0
Threshold limit of investments based on shareholders' equity (percent)	10.00%
Securities on deposit with state insurance departments	$ 47.1
Business owned life insurance cost	33
Fixed maturities
Debt Securities, Available-for-sale [Line Items]
FAL deposit assets	123.4
Short-term investments
Debt Securities, Available-for-sale [Line Items]
FAL deposit assets	$ 19.3

Investments - Investments Held

Investments - Investments Held in a Loss Position (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Fair value, total	$ 1,465,727	$ 850,838
Unrealized loss, total	32,706	9,556
Fair value, less than 12 months	634,958	603,468
Unrealized loss, less than 12 months	9,823	4,314
Fair value, 12 months or longer	830,769	247,370
Unrealized loss, 12 months or longer	22,883	5,242
U.S. Treasury obligations
Debt Securities, Available-for-sale [Line Items]
Fair value, total	97,969	110,788
Unrealized loss, total	1,405	1,181
Fair value, less than 12 months	20,221	67,135
Unrealized loss, less than 12 months	119	554
Fair value, 12 months or longer	77,748	43,653
Unrealized loss, 12 months or longer	1,286	627
U.S. Government-sponsored enterprise obligations
Debt Securities, Available-for-sale [Line Items]
Fair value, total	33,677	17,032
Unrealized loss, total	429	206
Fair value, less than 12 months	20,479	10,182
Unrealized loss, less than 12 months	126	64
Fair value, 12 months or longer	13,198	6,850
Unrealized loss, 12 months or longer	303	142
State and municipal bonds
Debt Securities, Available-for-sale [Line Items]
Fair value, total	63,094	23,122
Unrealized loss, total	648	419
Fair value, less than 12 months	30,924	15,168
Unrealized loss, less than 12 months	143	102
Fair value, 12 months or longer	32,170	7,954
Unrealized loss, 12 months or longer	505	317
Corporate debt
Debt Securities, Available-for-sale [Line Items]
Fair value, total	938,651	487,578
Unrealized loss, total	24,429	5,707
Fair value, less than 12 months	447,891	365,541
Unrealized loss, less than 12 months	8,804	2,730
Fair value, 12 months or longer	490,760	122,037
Unrealized loss, 12 months or longer	15,625	2,977
Residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Fair value, total	157,120	109,659
Unrealized loss, total	4,039	1,335
Fair value, less than 12 months	27,311	64,121
Unrealized loss, less than 12 months	209	402
Fair value, 12 months or longer	129,809	45,538
Unrealized loss, 12 months or longer	3,830	933
Agency commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Fair value, total	9,822	4,423
Unrealized loss, total	200	108
Fair value, less than 12 months	4,566	2,458
Unrealized loss, less than 12 months	22	34
Fair value, 12 months or longer	5,256	1,965
Unrealized loss, 12 months or longer	178	74
Other commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Fair value, total	22,924	12,878
Unrealized loss, total	375	134
Fair value, less than 12 months	13,348	7,939
Unrealized loss, less than 12 months	164	82
Fair value, 12 months or longer	9,576	4,939
Unrealized loss, 12 months or longer	211	52
Other asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Fair value, total	142,470	85,358
Unrealized loss, total	1,181	466
Fair value, less than 12 months	70,218	70,924
Unrealized loss, less than 12 months	236	346
Fair value, 12 months or longer	72,252	14,434
Unrealized loss, 12 months or longer	$ 945	$ 120

Investments - Investments Hel_2

Investments - Investments Held in a Loss Position Narrative (Details) - Non Government-Backed $ in Millions	Dec. 31, 2018USD ($)IssuerSecurity	Dec. 31, 2017USD ($)IssuerSecurity
Debt Securities, Available-for-sale [Line Items]
Debt securities in unrealized loss position (in securities) | Security	1,044	629
Debt securities in unrealized loss position as percentage of total debt securities held (percent)	50.60%	26.50%
Number of issuers in unrealized loss position (in issuers) | Issuer	550	375
Single greatest unrealized loss position	$ 0.6	$ 0.4
Second greatest unrealized loss position	$ 0.5	$ 0.3

Investments - Sales and Purchas

Investments - Sales and Purchases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Proceeds from sales (exclusive of maturities and paydowns)	$ 599,600	$ 530,200	$ 361,800
Purchases	$ 780,698	$ 614,440	$ 636,377

Investments - Net Investment In

Investments - Net Investment Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Securities, Available-for-sale [Line Items]
Investment fees and expenses	$ (6,681)	$ (6,977)	$ (6,103)
Net investment income	91,884	95,662	100,012
Fixed maturities
Debt Securities, Available-for-sale [Line Items]
Investment income	69,515	75,669	85,818
Equities
Debt Securities, Available-for-sale [Line Items]
Investment income	21,418	17,198	14,887
Short-term investments, including Other
Debt Securities, Available-for-sale [Line Items]
Investment income	5,649	7,793	3,402
BOLI
Debt Securities, Available-for-sale [Line Items]
Investment income	$ 1,983	$ 1,979	$ 2,008

Investments - Investments in Un

Investments - Investments in Unconsolidated Subsidiaries (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Investment in unconsolidated subsidiaries	$ 367,757	$ 330,591
Qualified affordable housing project tax credit partnerships
Schedule of Equity Method Investments [Line Items]
Investment in unconsolidated subsidiaries	65,677	84,607
Other tax credit partnerships
Schedule of Equity Method Investments [Line Items]
Investment in unconsolidated subsidiaries	3,757	6,118
All other investments, primarily LPs/LLCs
Schedule of Equity Method Investments [Line Items]
Investment in unconsolidated subsidiaries	$ 298,323	$ 239,866

Investments - Investments in _2

Investments - Investments in Unconsolidated Subsidiaries Narrative (Details) $ in Thousands	Dec. 31, 2018USD ($)Businessinvestment_interest	Dec. 31, 2017USD ($)
Debt Securities, Available-for-sale [Line Items]
Investment in unconsolidated subsidiaries	$ 367,757	$ 330,591
Number of LPs / LLCs with investment ownership percent over 25% (in businesses) | Business	1
Tax Credit Partnerships Almost 100% Ownership
Debt Securities, Available-for-sale [Line Items]
Number of tax credit partnerships almost 100% ownership percentage (in investment interest) | investment_interest	2
Investment in unconsolidated subsidiaries	$ 25,000	32,500
Tax Credit Partnerships Almost 100% Ownership | Maximum
Debt Securities, Available-for-sale [Line Items]
Ownership percentage of unconsolidated subsidiaries	100.00%
Percentage ownership (greater than) (percent)	100.00%
Tax Credit Partnerships Less Than 20% Ownership
Debt Securities, Available-for-sale [Line Items]
Investment in unconsolidated subsidiaries	$ 40,700	52,100
Tax Credit Partnerships Less Than 20% Ownership | Maximum
Debt Securities, Available-for-sale [Line Items]
Ownership percentage of unconsolidated subsidiaries	20.00%
Other Limited Partnerships and Limited Liability Company, Greater Than 25 Percent Ownership
Debt Securities, Available-for-sale [Line Items]
Investment in unconsolidated subsidiaries	$ 25,900	30,800
Percentage ownership (greater than) (percent)	25.00%
Other Limited Partnerships and Limited Liability Company Less than 25% Ownership
Debt Securities, Available-for-sale [Line Items]
Investment in unconsolidated subsidiaries	$ 272,400	$ 209,100
Percentage ownership (greater than) (percent)	25.00%

Investments - Equity in Earning

Investments - Equity in Earnings (Loss) of Unconsolidated Subsidiaries (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Losses from qualified affordable housing project tax credit investments	$ 18,889	$ 14,297	$ 20,047
Tax credits related to qualified affordable housing investments	18,474	17,774	18,531
Losses from historical projects	5,434	6,355	4,771
Historical tax credits	$ 2,567	$ 5,337	$ 9,018

Investments - Net Realized Inve

Investments - Net Realized Investment Gains (Losses) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Total other-than-temporary impairment losses:
OTTI losses	$ (490)	$ (13,200)	$ (10,834)
Portion of OTTI losses recognized in other comprehensive income before taxes	0	248	1,068
Net impairment losses recognized in earnings	(490)	(12,952)	(9,766)
Gross realized gains, available-for-sale fixed maturities	5,942	6,653	12,451
Gross realized (losses), available-for-sale fixed maturities	(5,799)	(3,123)	(7,038)
Net realized gains (losses), short-term investments	(1)	(2)	18
Net realized gains (losses), trading fixed maturities	(100)	0	0
Net realized gains (losses), equity investments	12,230	10,724	6,632
Net realized gains (losses), other investments	1,340	2,963	1,115
Change in unrealized holding gains (losses), trading fixed maturities	(317)	0	0
Change in unrealized holding gains (losses), equity investments	(52,707)	11,243	30,557
Change in unrealized holding gains (losses), convertible securities, carried at fair value	(3,849)	896	899
Other	263	7	7
Total net realized investment gains (losses)	(43,488)	16,409	34,875
State and municipal bonds
Total other-than-temporary impairment losses:
OTTI losses	0	(850)	(100)
Corporate debt
Total other-than-temporary impairment losses:
OTTI losses	(490)	(419)	(7,604)
Portion of OTTI losses recognized in other comprehensive income before taxes		248	1,068
Net impairment losses recognized in earnings		(200)
Investment in unconsolidated subsidiaries
Total other-than-temporary impairment losses:
OTTI losses	0	(11,931)	0
Other investments
Total other-than-temporary impairment losses:
OTTI losses	$ 0	$ 0	$ (3,130)

Investments - Net Realized In_2

Investments - Net Realized Investment Gains (Losses) Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Securities, Available-for-sale [Line Items]
OTTI loss, debt securities, portion recognized in earnings	$ (490)	$ (12,952)	$ (9,766)
Credit-related OTTI	93	1,313	1,158	$ 5,751
Non-credit OTTI losses recognized in other comprehensive income	0	248	1,068
Investment Tax Credit Carryforward | Investment in unconsolidated subsidiaries
Debt Securities, Available-for-sale [Line Items]
OTTI loss, debt securities, portion recognized in earnings	$ (3,400)
Corporate debt
Debt Securities, Available-for-sale [Line Items]
OTTI loss, debt securities, portion recognized in earnings		(200)
Credit-related OTTI			5,500
Non-credit OTTI losses recognized in other comprehensive income		$ 248	1,068
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Non-credit OTTI losses recognized in other comprehensive income			$ 900

Investments - Credit Losses Rec

Investments - Credit Losses Recorded in Earnings (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cumulative credit losses recorded in earnings related to impaired debt securities
Beginning balance	$ 1,313	$ 1,158	$ 5,751
No OTTI has been previously recognized	0	171	2,398
OTTI has been previously recognized	0	0	2,154
Securities sold during the period (realized)	(1,220)	(16)	(9,145)
Ending balance	$ 93	$ 1,313	$ 1,158

Retroactive Insurance Contrac_2

Retroactive Insurance Contracts (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Net premiums earned	$ 202,033	$ 206,070	$ 223,591	$ 187,159	$ 182,972	$ 192,303	$ 180,353	$ 182,903	$ 818,853	$ 738,531	$ 733,281
Net losses and loss adjustment expenses									593,210	469,158	443,229
Gross liability for losses and loss adjustment expenses	$ 2,119,847				$ 2,048,381				2,119,847	$ 2,048,381	$ 1,993,428	$ 2,005,326
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
Gross liability for losses and loss adjustment expenses			$ 600
Prospective coverage for retroactive insurance contract
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Net premiums earned									7,900
Retroactive coverage for retroactive insurance contract
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Net premiums earned									$ 18,700

Reinsurance - Premiums Written

Reinsurance - Premiums Written and Earned (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Summary of the effect of reinsurance on premiums written and earned
Direct premiums written									$ 910,198	$ 842,968	$ 794,377
Assumed premiums written									47,113	31,908	40,637
Ceded premiums written									(122,397)	(110,858)	(96,481)
Net premiums written									834,914	764,018	738,533
Direct premiums earned									903,354	821,249	790,791
Assumed premiums earned									41,535	27,629	37,805
Ceded premiums earned									(126,036)	(110,347)	(95,315)
Net premiums earned	$ 202,033	$ 206,070	$ 223,591	$ 187,159	$ 182,972	$ 192,303	$ 180,353	$ 182,903	818,853	738,531	733,281
Losses and loss adjustment expenses									675,784	592,218	515,242
Reinsurance recoveries									(82,574)	(123,060)	(72,013)
Net losses and loss adjustment expenses									$ 593,210	$ 469,158	$ 443,229

Reinsurance - Narrative (Detail

Reinsurance - Narrative (Details)	12 Months Ended
	Dec. 31, 2018USD ($)reinsurer	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Ceded Credit Risk [Line Items]
Premium ceded reduction amount	$ (5,500,000)	$ 1,200,000	$ (7,100,000)
Amount due from reinsurers total	$ 340,400,000
Number of major reinsurers | reinsurer	0
Amount of reinsurance recoverables collateralized by letters of credit	$ 77,100,000
Allowance for reinsurance receivables	0	0
Loss on uncollectible accounts in the period			0
Cash receipt for reinsurance commutations	11,558,000	7,317,000
Assumed premiums earned	41,535,000	27,629,000	37,805,000
DDR Reinsurance Agreement
Ceded Credit Risk [Line Items]
Amount of reinsurance recoverables collateralized by letters of credit	5,400,000
Cash receipt for reinsurance commutations	7,800,000
Novation Agreement
Ceded Credit Risk [Line Items]
Assumed premiums earned			11,800,000
Specialty P&C
Ceded Credit Risk [Line Items]
Amount of reinsurance recoverables collateralized by letters of credit	6,700,000	6,600,000	7,100,000
Cash receipt for reinsurance commutations	6,100,000	$ 6,300,000	$ 6,800,000
Minimum
Ceded Credit Risk [Line Items]
Major reinsurer threshold	$ 36,000,000

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets
Unpaid loss discount	$ 30,629	$ 20,368
Unearned premium adjustment	16,620	14,449
Compensation related	9,879	11,467
Unrealized losses on investments, net	4,403	0
Basis differentials–investments	912	0
Intangibles	433	514
Foreign NOL	6,795	4,116
Total gross deferred tax assets	69,671	50,914
Valuation allowance	(7,074)	(4,116)
Total deferred tax assets, net of valuation allowance	62,597	46,798
Deferred tax liabilities
Deferred policy acquisition costs	(9,972)	(6,333)
Unpaid loss discount–transition	(10,128)	0
Unrealized gains on investments, net	0	(5,166)
Fixed assets	(542)	(826)
Basis differentials–investments	0	(10,397)
Intangibles	(11,243)	(12,548)
Other	(1,604)	(1,598)
Total deferred tax liabilities	(33,489)	(36,868)
Net deferred tax assets (liabilities)	$ 29,108	$ 9,930

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Contingency [Line Items]
Net operating loss carryforwards	$ 34,000,000
Foreign net operating loss carryforwards	6,795,000	$ 4,116,000
Increase in valuation allowance and related deferred tax asset	2,700,000
Deferred tax asset, net	29,108,000	9,930,000
Capital loss carryforward	0
Income tax receivable	3,500,000
Taxes payable		8,000,000
Unrecognized tax benefits that would impact effective tax rate	1,200,000	1,300,000
Interest expense
Income Tax Contingency [Line Items]
Income tax interest and penalties		300,000	$ 200,000
Accrued liability for interest	600,000	$ 500,000
Inova Re
Income Tax Contingency [Line Items]
Deferred tax asset, net	$ 300,000

Income Taxes - Unrecognized Tax

Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of unrecognized tax benefits
Balance at January 1	$ 5,341	$ 8,353	$ 8,195
Increases for tax positions taken during the current year	0	0	361
(Decreases) for tax positions taken during the current year	(777)	(3,500)	0
Decreases for tax positions taken during prior years	(800)
Increases for tax positions taken during prior years		700	0
(Decreases) relating to a lapse of the applicable statute of limitations	(163)	(212)	(203)
Balance at December 31	$ 3,601	$ 5,341	$ 8,353

Income Taxes - Components of Ta

Income Taxes - Components of Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current expense (benefit)
Federal and foreign	$ (6,509)	$ 19,546	$ 15,857
State	301	120	729
Total current expense (benefit)	(6,208)	19,666	16,586
Deferred expense (benefit)
Federal and foreign	(11,765)	1,331	8,284
State	(59)	362	250
Total deferred expense (benefit)	(11,824)	1,693	8,534
Total income tax expense (benefit)	$ (18,032)	$ 21,359	$ 25,120

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of expected income tax expense to actual income tax expense
Computed “expected” tax expense	$ 6,095	$ 45,018	$ 61,670
Tax-exempt income	(2,505)	(8,356)	(9,917)
Tax credits	(21,059)	(23,111)	(27,549)
Non-U.S. operating results	2,269	918	(1,688)
Excess tax benefit on share-based compensation	(275)	(2,762)	0
Change in federal corporate tax rate	0	6,541	0
Change in limitation of future deductibility of certain executive compensation	0	3,497	0
Provision-to-return differences	(2,309)	(1,979)	1,209
Other	(248)	1,593	1,395
Total income tax expense (benefit)	$ (18,032)	$ 21,359	$ 25,120

Deferred Policy Acquisition C_2

Deferred Policy Acquisition Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Insurance [Abstract]
Amortization of deferred policy acquisition costs	$ 104,501	$ 95,751	$ 88,378

Reserve for Losses and Loss A_3

Reserve for Losses and Loss Adjustment Expenses - Narrative and Activity in the Reserve (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018USD ($)partition	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2018USD ($)partition	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Loss Contingencies [Line Items]
Paid losses and loss adjustment expenses, net of reinsurance									$ 529,979	$ 476,315	$ 479,252
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease) [Abstract]
Minimum period for claims resolution (years)									5 years
Number of business partitions (in partitions) | partition	200								200
Summary of reserve for losses and loss adjustment expenses
Balance, beginning of year				$ 2,048,381				$ 1,993,428	$ 2,048,381	1,993,428	2,005,326
Less reinsurance recoverables on unpaid losses and loss adjustment expenses				335,585				273,475	335,585	273,475	249,350
Net balance, beginning of year				1,712,796				1,719,953	1,712,796	1,719,953	1,755,976
Net losses:
Current year	$ 179,056	$ 169,154	$ 184,543	152,572	$ 149,399	$ 161,631	$ 144,562	147,927	685,326	603,518	587,007
Favorable development of reserves established in prior years, net	(24,967)	(21,549)	(22,815)	$ (22,786)	(44,297)	$ (32,275)	$ (29,012)	$ (28,776)	(92,116)	(134,360)	(143,778)
Total									593,210	469,158	443,229
Paid related to:
Current year									(117,268)	(106,633)	(96,190)
Prior years									(412,711)	(369,682)	(383,062)
Total paid									(529,979)	(476,315)	(479,252)
Net balance, end of year	1,776,027				1,712,796				1,776,027	1,712,796	1,719,953
Plus reinsurance recoverables on unpaid losses and loss adjustment expenses	343,820				335,585				343,820	335,585	273,475
Balance, end of year	$ 2,119,847				$ 2,048,381				$ 2,119,847	$ 2,048,381	$ 1,993,428
Retroactive insurance contract
Loss Contingencies [Line Items]
Paid losses and loss adjustment expenses, net of reinsurance			25,400
Summary of reserve for losses and loss adjustment expenses
Balance, beginning of year		$ 600
Paid related to:
Balance, end of year			$ 600

Reserve for Losses and Loss A_4

Reserve for Losses and Loss Adjustment Expenses - Claim Development (Details) $ in Thousands	Dec. 31, 2018USD ($)reported_claim	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2012USD ($)	Mar. 31, 2011USD ($)	Dec. 31, 2010USD ($)	Dec. 31, 2009USD ($)
Claims Development [Line Items]
Liabilities for losses and loss adjustment expenses, net of reinsurance	$ 1,596,838
Healthcare Professional Liability Claims-Made
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,694,095
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,683,850
All outstanding liabilities, net of reinsurance	11,724
Liabilities for losses and loss adjustment expenses, net of reinsurance	1,021,969
Healthcare Professional Liability Claims-Made | 2009
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	220,703	$ 224,768	$ 230,849	$ 246,146	$ 265,478	$ 284,511	$ 320,368	$ 345,714	$ 370,642	$ 379,259
Incurred but Not Reported Liabilities (IBNR)	$ (455)
Cumulative Number of Reported Claims | reported_claim	3,828
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 213,568	209,016	205,372	200,425	191,420	178,445	153,563	114,318	71,272	15,051
Healthcare Professional Liability Claims-Made | 2010
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	257,714	258,466	270,484	279,713	291,553	312,813	338,170	354,787	364,996
Incurred but Not Reported Liabilities (IBNR)	$ (243)
Cumulative Number of Reported Claims | reported_claim	3,847
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 243,675	240,945	236,171	221,693	209,777	180,432	137,712	69,551	15,464
Healthcare Professional Liability Claims-Made | 2011
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	254,329	264,777	278,258	289,400	305,540	331,884	344,808	348,916
Incurred but Not Reported Liabilities (IBNR)	$ (2,091)
Cumulative Number of Reported Claims | reported_claim	3,532
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 233,103	224,982	214,502	198,112	177,089	133,004	71,208	14,417
Healthcare Professional Liability Claims-Made | 2012
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	271,110	279,589	291,075	306,956	319,613	324,418	341,289
Incurred but Not Reported Liabilities (IBNR)	$ 276
Cumulative Number of Reported Claims | reported_claim	3,702
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 244,512	231,652	215,220	190,997	145,488	73,571	15,382
Healthcare Professional Liability Claims-Made | 2013
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	258,251	272,364	287,140	296,550	304,209	315,346
Incurred but Not Reported Liabilities (IBNR)	$ 173
Cumulative Number of Reported Claims | reported_claim	3,783
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 213,879	197,265	171,681	127,496	69,657	16,938
Healthcare Professional Liability Claims-Made | 2014
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	256,968	267,442	280,043	289,397	290,020
Incurred but Not Reported Liabilities (IBNR)	$ (5,200)
Cumulative Number of Reported Claims | reported_claim	3,320
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 186,239	154,236	116,791	59,485	16,764
Healthcare Professional Liability Claims-Made | 2015
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	270,814	271,138	269,980	276,492
Incurred but Not Reported Liabilities (IBNR)	$ (8,030)
Cumulative Number of Reported Claims | reported_claim	3,266
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 161,896	111,741	55,731	9,172
Healthcare Professional Liability Claims-Made | 2016
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	287,551	274,643	271,765
Incurred but Not Reported Liabilities (IBNR)	$ (21,456)
Cumulative Number of Reported Claims | reported_claim	3,481
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 109,756	51,869	9,027
Healthcare Professional Liability Claims-Made | 2017
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	295,883	283,746
Incurred but Not Reported Liabilities (IBNR)	$ (11,228)
Cumulative Number of Reported Claims | reported_claim	3,677
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 63,171	16,309
Healthcare Professional Liability Claims-Made | 2018
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	320,772
Incurred but Not Reported Liabilities (IBNR)	$ 129,334
Cumulative Number of Reported Claims | reported_claim	3,558
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 14,051
Healthcare Professional Liability Occurrence
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	292,713
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	130,757
All outstanding liabilities, net of reinsurance	7,985
Liabilities for losses and loss adjustment expenses, net of reinsurance	169,941
Healthcare Professional Liability Occurrence | 2009
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	23,387	24,572	26,340	28,731	32,675	34,099	37,437	36,802	35,366	34,450
Incurred but Not Reported Liabilities (IBNR)	$ 1,519
Cumulative Number of Reported Claims | reported_claim	246
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 17,022	16,270	16,025	15,380	13,248	10,823	7,947	5,067	2,255	175
Healthcare Professional Liability Occurrence | 2010
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	26,501	29,338	33,361	35,831	37,920	42,233	43,195	43,238	41,721
Incurred but Not Reported Liabilities (IBNR)	$ 946
Cumulative Number of Reported Claims | reported_claim	290
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 23,832	23,313	22,804	21,837	15,147	9,120	5,647	1,881	285
Healthcare Professional Liability Occurrence | 2011
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	29,784	32,343	35,004	37,150	39,917	41,453	44,956	45,882
Incurred but Not Reported Liabilities (IBNR)	$ 2,136
Cumulative Number of Reported Claims | reported_claim	342
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 24,539	23,194	21,416	19,197	16,544	8,059	2,803	291
Healthcare Professional Liability Occurrence | 2012
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	29,857	32,691	34,774	40,692	44,848	46,513	45,703
Incurred but Not Reported Liabilities (IBNR)	$ 3,816
Cumulative Number of Reported Claims | reported_claim	399
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 23,095	21,435	19,275	12,212	7,705	2,430	363
Healthcare Professional Liability Occurrence | 2013
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	26,919	30,906	34,393	35,624	36,602	32,746
Incurred but Not Reported Liabilities (IBNR)	$ 971
Cumulative Number of Reported Claims | reported_claim	356
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 18,949	16,787	14,753	7,826	3,170	369
Healthcare Professional Liability Occurrence | 2014
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	25,885	29,869	32,143	29,918	30,420
Incurred but Not Reported Liabilities (IBNR)	$ 2,778
Cumulative Number of Reported Claims | reported_claim	355
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 14,604	10,519	7,460	2,260	394
Healthcare Professional Liability Occurrence | 2015
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	40,960	37,346	35,347	35,648
Incurred but Not Reported Liabilities (IBNR)	$ 4,667
Cumulative Number of Reported Claims | reported_claim	355
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 11,626	4,854	786	(350)
Healthcare Professional Liability Occurrence | 2016
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	27,240	28,790	29,609
Incurred but Not Reported Liabilities (IBNR)	$ 6,244
Cumulative Number of Reported Claims | reported_claim	322
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 2,883	(195)	(182)
Healthcare Professional Liability Occurrence | 2017
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	23,760	24,571
Incurred but Not Reported Liabilities (IBNR)	$ 19,890
Cumulative Number of Reported Claims | reported_claim	270
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ (5,858)	(6,809)
Healthcare Professional Liability Occurrence | 2018
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	38,420
Incurred but Not Reported Liabilities (IBNR)	$ 36,196
Cumulative Number of Reported Claims | reported_claim	118
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 65
Medical Technology and Life Sciences Liability Reserves
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	94,719
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	59,621
All outstanding liabilities, net of reinsurance	1,101
Liabilities for losses and loss adjustment expenses, net of reinsurance	36,199
Medical Technology and Life Sciences Liability Reserves | 2009
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	17,984	18,176	19,264	20,551	21,733	23,425	26,181	27,523	31,183	30,462
Incurred but Not Reported Liabilities (IBNR)	$ 251
Cumulative Number of Reported Claims | reported_claim	699
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 17,522	16,515	15,186	15,184	15,097	14,933	14,675	7,742	5,071	116
Medical Technology and Life Sciences Liability Reserves | 2010
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	18,611	16,878	16,047	17,439	19,315	23,307	25,175	27,063	26,077
Incurred but Not Reported Liabilities (IBNR)	$ 402
Cumulative Number of Reported Claims | reported_claim	498
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 17,660	15,366	12,253	12,146	11,725	12,283	8,491	3,557	485
Medical Technology and Life Sciences Liability Reserves | 2011
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	8,202	12,358	12,487	13,794	15,836	19,166	20,930	17,249
Incurred but Not Reported Liabilities (IBNR)	$ 500
Cumulative Number of Reported Claims | reported_claim	521
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 7,664	7,799	7,240	7,376	5,062	3,846	2,034	118
Medical Technology and Life Sciences Liability Reserves | 2012
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	5,051	4,797	5,824	7,441	8,906	9,989	11,162
Incurred but Not Reported Liabilities (IBNR)	$ 732
Cumulative Number of Reported Claims | reported_claim	220
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 3,800	3,676	3,366	3,247	2,805	1,520	568
Medical Technology and Life Sciences Liability Reserves | 2013
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	3,566	4,697	7,226	9,536	9,955	9,807
Incurred but Not Reported Liabilities (IBNR)	$ 380
Cumulative Number of Reported Claims | reported_claim	218
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 3,102	3,092	2,599	1,967	1,029	102
Medical Technology and Life Sciences Liability Reserves | 2014
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	7,679	8,984	9,012	10,306	9,989
Incurred but Not Reported Liabilities (IBNR)	$ 2,544
Cumulative Number of Reported Claims | reported_claim	272
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 3,724	3,046	2,564	1,527	388
Medical Technology and Life Sciences Liability Reserves | 2015
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	5,929	7,193	8,757	9,376
Incurred but Not Reported Liabilities (IBNR)	$ 2,770
Cumulative Number of Reported Claims | reported_claim	155
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 2,097	1,625	440	25
Medical Technology and Life Sciences Liability Reserves | 2016
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	7,413	8,467	9,200
Incurred but Not Reported Liabilities (IBNR)	$ 3,482
Cumulative Number of Reported Claims | reported_claim	180
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 2,365	1,690	53
Medical Technology and Life Sciences Liability Reserves | 2017
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	10,143	11,049
Incurred but Not Reported Liabilities (IBNR)	$ 7,834
Cumulative Number of Reported Claims | reported_claim	95
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 1,681	56
Medical Technology and Life Sciences Liability Reserves | 2018
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	10,141
Incurred but Not Reported Liabilities (IBNR)	$ 9,818
Cumulative Number of Reported Claims | reported_claim	188
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 6
Workers' compensation insurance
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	838,821
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	685,504
All outstanding liabilities, net of reinsurance	2,208
Liabilities for losses and loss adjustment expenses, net of reinsurance	155,525
Workers' compensation insurance | 2009
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	47,480	47,480	47,480	47,905	48,372	47,811	45,354	45,354	45,354	45,354
Incurred but Not Reported Liabilities (IBNR)	$ 80
Cumulative Number of Reported Claims | reported_claim	10,129
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 47,189	47,089	47,012	46,928	46,321	45,689	43,436	39,351	31,465	14,701
Workers' compensation insurance | 2010
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	54,600	54,600	54,600	55,200	54,779	54,837	55,852	55,852	55,852
Incurred but Not Reported Liabilities (IBNR)	$ 58
Cumulative Number of Reported Claims | reported_claim	12,913
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 54,014	53,974	53,734	53,443	52,530	51,117	46,762	39,098	20,086
Workers' compensation insurance | 2011
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	72,795	72,795	72,495	72,420	72,280	71,521	65,783	65,665
Incurred but Not Reported Liabilities (IBNR)	$ 354
Cumulative Number of Reported Claims | reported_claim	15,244
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 71,856	71,662	70,934	70,146	67,945	62,307	50,900	21,993
Workers' compensation insurance | 2012
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	75,136	75,636	75,836	76,357	75,848	76,551	80,285
Incurred but Not Reported Liabilities (IBNR)	$ 724
Cumulative Number of Reported Claims | reported_claim	16,204
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 73,676	73,662	72,766	70,558	65,908	56,122	27,448
Workers' compensation insurance | 2013
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	88,810	88,810	88,010	86,928	85,935	86,973
Incurred but Not Reported Liabilities (IBNR)	$ 1,017
Cumulative Number of Reported Claims | reported_claim	16,429
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 86,783	85,689	82,369	76,813	63,825	30,554
Workers' compensation insurance | 2014
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	92,229	92,229	93,029	93,529	93,019
Incurred but Not Reported Liabilities (IBNR)	$ 3,350
Cumulative Number of Reported Claims | reported_claim	16,210
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 87,314	85,022	77,631	65,922	30,368
Workers' compensation insurance | 2015
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	97,654	98,454	100,454	100,101
Incurred but Not Reported Liabilities (IBNR)	$ 8,522
Cumulative Number of Reported Claims | reported_claim	16,548
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 83,483	78,947	65,070	32,078
Workers' compensation insurance | 2016
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	92,148	97,348	101,348
Incurred but Not Reported Liabilities (IBNR)	$ 13,540
Cumulative Number of Reported Claims | reported_claim	15,972
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 69,237	58,192	28,377
Workers' compensation insurance | 2017
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	99,874	99,874
Incurred but Not Reported Liabilities (IBNR)	$ 12,489
Cumulative Number of Reported Claims | reported_claim	16,058
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 70,333	31,586
Workers' compensation insurance | 2018
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	118,095
Incurred but Not Reported Liabilities (IBNR)	$ 32,816
Cumulative Number of Reported Claims | reported_claim	17,556
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 41,619
Segregated Portfolio Cell Reinsurance
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	266,016
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	210,411
All outstanding liabilities, net of reinsurance	912
Liabilities for losses and loss adjustment expenses, net of reinsurance	56,517
Segregated Portfolio Cell Reinsurance | 2009
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	15,279	15,277	15,277	15,618	15,695	15,809	15,948	15,886	16,337	17,790
Incurred but Not Reported Liabilities (IBNR)	$ 107
Cumulative Number of Reported Claims | reported_claim	2,962
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 15,172	15,166	15,165	15,147	14,954	14,881	14,660	13,202	10,782	$ 5,000
Segregated Portfolio Cell Reinsurance | 2010
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	17,224	17,278	17,320	17,541	17,736	17,825	17,715	18,265	19,767
Incurred but Not Reported Liabilities (IBNR)	$ 275
Cumulative Number of Reported Claims | reported_claim	2,914
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 16,904	16,850	16,810	16,842	16,757	16,214	15,087	12,904	$ 6,503
Segregated Portfolio Cell Reinsurance | 2011
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	18,606	18,666	18,725	18,644	19,282	19,629	19,360	18,790
Incurred but Not Reported Liabilities (IBNR)	$ 363
Cumulative Number of Reported Claims | reported_claim	3,154
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 18,185	18,176	18,177	18,054	17,869	17,197	14,045	$ 5,940
Segregated Portfolio Cell Reinsurance | 2012
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	19,799	19,864	19,972	20,028	21,048	21,513	22,940
Incurred but Not Reported Liabilities (IBNR)	$ 441
Cumulative Number of Reported Claims | reported_claim	3,454
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 19,328	19,402	19,208	18,474	17,728	14,740	$ 7,808
Segregated Portfolio Cell Reinsurance | 2013
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	26,033	26,260	26,619	26,758	25,310	23,809
Incurred but Not Reported Liabilities (IBNR)	$ 544
Cumulative Number of Reported Claims | reported_claim	3,723
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 25,489	25,366	25,209	24,268	19,054	$ 8,131
Segregated Portfolio Cell Reinsurance | 2014
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	28,281	28,373	29,000	28,423	28,248
Incurred but Not Reported Liabilities (IBNR)	$ 942
Cumulative Number of Reported Claims | reported_claim	4,433
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 26,959	26,810	26,173	21,880	9,933
Segregated Portfolio Cell Reinsurance | 2015
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	27,548	28,746	32,519	36,423
Incurred but Not Reported Liabilities (IBNR)	$ 1,601
Cumulative Number of Reported Claims | reported_claim	4,949
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 24,781	23,977	21,706	11,257
Segregated Portfolio Cell Reinsurance | 2016
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	30,998	34,055	37,601
Incurred but Not Reported Liabilities (IBNR)	$ 2,528
Cumulative Number of Reported Claims | reported_claim	5,326
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 26,285	23,003	10,980
Segregated Portfolio Cell Reinsurance | 2017
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	38,594	42,725
Incurred but Not Reported Liabilities (IBNR)	$ 7,314
Cumulative Number of Reported Claims | reported_claim	5,699
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 24,791	12,404
Segregated Portfolio Cell Reinsurance | 2018
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	43,654
Incurred but Not Reported Liabilities (IBNR)	$ 18,788
Cumulative Number of Reported Claims | reported_claim	6,228
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 12,517
Syndicate 1729 casualty
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	79,768
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	38,289
All outstanding liabilities, net of reinsurance	0
Liabilities for losses and loss adjustment expenses, net of reinsurance	41,479
Syndicate 1729 casualty | 2012
Claims Development [Line Items]
Incurred but Not Reported Liabilities (IBNR)	1,086
Syndicate 1729 casualty | 2014
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	5,472	5,547	5,610	5,812	6,110
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	4,320	4,214	4,092	474	20
Syndicate 1729 casualty | 2015
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	14,232	14,398	14,510	14,810
Incurred but Not Reported Liabilities (IBNR)	1,984
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	10,947	10,313	6,307	724
Syndicate 1729 casualty | 2016
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	19,552	19,669	19,535
Incurred but Not Reported Liabilities (IBNR)	5,098
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	12,869	8,441	2,495
Syndicate 1729 casualty | 2017
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	21,824	22,069
Incurred but Not Reported Liabilities (IBNR)	9,960
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	8,301	2,611
Syndicate 1729 casualty | 2018
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	18,688
Incurred but Not Reported Liabilities (IBNR)	16,014
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,852
Syndicate 1729 property insurance
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	58,118
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	44,426
All outstanding liabilities, net of reinsurance	0
Liabilities for losses and loss adjustment expenses, net of reinsurance	13,692
Syndicate 1729 property insurance | 2014
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	866	864	888	1,089	890
Incurred but Not Reported Liabilities (IBNR)	$ (6)
Cumulative Number of Reported Claims | reported_claim	118
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 857	854	836	1,005	267
Syndicate 1729 property insurance | 2015
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	6,159	6,194	5,917	5,519
Incurred but Not Reported Liabilities (IBNR)	$ 1,128
Cumulative Number of Reported Claims | reported_claim	921
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 4,869	4,808	4,022	3,165
Syndicate 1729 property insurance | 2016
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	12,823	12,984	11,896
Incurred but Not Reported Liabilities (IBNR)	$ 12
Cumulative Number of Reported Claims | reported_claim	2,484
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 12,343	10,939	7,751
Syndicate 1729 property insurance | 2017
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	17,634	15,018
Incurred but Not Reported Liabilities (IBNR)	$ (883)
Cumulative Number of Reported Claims | reported_claim	4,240
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 16,439	8,221
Syndicate 1729 property insurance | 2018
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	20,636
Incurred but Not Reported Liabilities (IBNR)	$ 6,898
Cumulative Number of Reported Claims | reported_claim	3,681
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 9,918
Syndicate 1729 property reinsurance
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	23,493
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	13,342
All outstanding liabilities, net of reinsurance	0
Liabilities for losses and loss adjustment expenses, net of reinsurance	10,151
Syndicate 1729 property reinsurance | 2014
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,125	989	989	929	831
Incurred but Not Reported Liabilities (IBNR)	0
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,125	984	984	917	$ 79
Syndicate 1729 property reinsurance | 2015
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,328	2,275	2,825	2,788
Incurred but Not Reported Liabilities (IBNR)	(91)
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,234	1,996	1,804	$ 1,313
Syndicate 1729 property reinsurance | 2016
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	3,368	4,050	4,497
Incurred but Not Reported Liabilities (IBNR)	943
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,136	1,667	$ 613
Syndicate 1729 property reinsurance | 2017
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	7,832	6,861
Incurred but Not Reported Liabilities (IBNR)	371
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	7,300	$ 4,147
Syndicate 1729 property reinsurance | 2018
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	8,840
Incurred but Not Reported Liabilities (IBNR)	8,154
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 547

Reserve for Losses and Loss A_5

Reserve for Losses and Loss Adjustment Expenses - Historical Claims Duration (Details)	Dec. 31, 2018
Healthcare Professional Liability Claims-Made
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Historical claims duration, year 1 (percent)	5.40%
Historical claims duration, year 2 (percent)	19.50%
Historical claims duration, year 3 (percent)	22.80%
Historical claims duration, year 4 (percent)	17.00%
Historical claims duration, year 5 (percent)	10.40%
Historical claims duration, year 6 (percent)	5.90%
Historical claims duration, year 7 (percent)	4.60%
Historical claims duration, year 8 (percent)	2.40%
Historical claims duration, year 9 (percent)	1.40%
Historical claims duration, year 10 (percent)	2.10%
Healthcare Professional Liability Occurrence
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Historical claims duration, year 1 (percent)	(2.30%)
Historical claims duration, year 2 (percent)	6.10%
Historical claims duration, year 3 (percent)	15.00%
Historical claims duration, year 4 (percent)	17.60%
Historical claims duration, year 5 (percent)	15.20%
Historical claims duration, year 6 (percent)	11.70%
Historical claims duration, year 7 (percent)	6.10%
Historical claims duration, year 8 (percent)	3.10%
Historical claims duration, year 9 (percent)	1.50%
Historical claims duration, year 10 (percent)	3.20%
Medical technology liability
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Historical claims duration, year 1 (percent)	2.60%
Historical claims duration, year 2 (percent)	19.10%
Historical claims duration, year 3 (percent)	19.70%
Historical claims duration, year 4 (percent)	16.40%
Historical claims duration, year 5 (percent)	8.60%
Historical claims duration, year 6 (percent)	1.60%
Historical claims duration, year 7 (percent)	2.60%
Historical claims duration, year 8 (percent)	5.00%
Historical claims duration, year 9 (percent)	9.90%
Historical claims duration, year 10 (percent)	5.60%
Workers' compensation insurance
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Historical claims duration, year 1 (percent)	33.20%
Historical claims duration, year 2 (percent)	36.50%
Historical claims duration, year 3 (percent)	14.10%
Historical claims duration, year 4 (percent)	7.10%
Historical claims duration, year 5 (percent)	3.30%
Historical claims duration, year 6 (percent)	1.30%
Historical claims duration, year 7 (percent)	0.70%
Historical claims duration, year 8 (percent)	0.30%
Historical claims duration, year 9 (percent)	0.10%
Historical claims duration, year 10 (percent)	0.20%
Segregated Portfolio Cell Reinsurance
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Historical claims duration, year 1 (percent)	34.50%
Historical claims duration, year 2 (percent)	38.50%
Historical claims duration, year 3 (percent)	14.30%
Historical claims duration, year 4 (percent)	4.60%
Historical claims duration, year 5 (percent)	1.70%
Historical claims duration, year 6 (percent)	0.60%
Historical claims duration, year 7 (percent)	0.20%
Historical claims duration, year 8 (percent)	0.10%
Historical claims duration, year 9 (percent)	0.20%
Historical claims duration, year 10 (percent)	0.00%
Syndicate 1729 casualty
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Historical claims duration, year 1 (percent)	18.70%
Historical claims duration, year 2 (percent)	40.30%
Historical claims duration, year 3 (percent)	22.60%
Historical claims duration, year 4 (percent)	12.80%
Historical claims duration, year 5 (percent)	3.20%
Historical claims duration, year 6 (percent)	1.10%
Historical claims duration, year 7 (percent)	1.00%
Historical claims duration, year 8 (percent)	0.40%
Historical claims duration, year 9 (percent)	0.00%
Historical claims duration, year 10 (percent)	0.00%
Lloyd's Syndicate Property Insurance [Member]
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Historical claims duration, year 1 (percent)	81.40%
Historical claims duration, year 2 (percent)	15.90%
Historical claims duration, year 3 (percent)	2.10%
Historical claims duration, year 4 (percent)	0.20%
Historical claims duration, year 5 (percent)	0.20%
Historical claims duration, year 6 (percent)	0.10%
Historical claims duration, year 7 (percent)	0.10%
Historical claims duration, year 8 (percent)	0.10%
Historical claims duration, year 9 (percent)	0.00%
Historical claims duration, year 10 (percent)	0.00%
Lloyd's Syndicate Property Reinsurance [Member]
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Historical claims duration, year 1 (percent)	82.00%
Historical claims duration, year 2 (percent)	13.30%
Historical claims duration, year 3 (percent)	2.80%
Historical claims duration, year 4 (percent)	1.10%
Historical claims duration, year 5 (percent)	0.40%
Historical claims duration, year 6 (percent)	0.20%
Historical claims duration, year 7 (percent)	0.10%
Historical claims duration, year 8 (percent)	0.00%
Historical claims duration, year 9 (percent)	0.00%
Historical claims duration, year 10 (percent)	0.00%

Reserve for Losses and Loss A_6

Reserve for Losses and Loss Adjustment Expenses - Reconciliation of Claims Development (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	$ 1,596,838
Total reinsurance recoverable on unpaid losses and loss adjustment expenses	343,820	$ 335,585	$ 273,475	$ 249,350
Reserve for the future utilization of the DDR benefit	67,200
Unallocated loss adjustment expenses	100,123
Loss portfolio transfer	18,252
Purchase accounting	1,551
Other	(7,937)
Liability for unpaid claims and claim adjustment expense	179,189
Gross liability for losses and loss adjustment expenses	2,119,847	$ 2,048,381	$ 1,993,428	$ 2,005,326
Healthcare professional liability claims-made
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	1,021,969
Total reinsurance recoverable on unpaid losses and loss adjustment expenses	151,870
Healthcare professional liability occurrence
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	169,941
Total reinsurance recoverable on unpaid losses and loss adjustment expenses	37,683
Medical technology liability
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	36,199
Total reinsurance recoverable on unpaid losses and loss adjustment expenses	32,604
Workers' compensation insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	155,525
Total reinsurance recoverable on unpaid losses and loss adjustment expenses	67,631
Segregated Portfolio Cell Reinsurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	56,517
Total reinsurance recoverable on unpaid losses and loss adjustment expenses	24,177
Syndicate 1729 casualty
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	41,479
Total reinsurance recoverable on unpaid losses and loss adjustment expenses	678
Syndicate 1729 property insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	13,692
Total reinsurance recoverable on unpaid losses and loss adjustment expenses	10,323
Syndicate 1729 property reinsurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	10,151
Total reinsurance recoverable on unpaid losses and loss adjustment expenses	9,717
Other short-duration lines
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities	91,365
Total reinsurance recoverable on unpaid losses and loss adjustment expenses	$ 9,137

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2018GBP (£)	Feb. 28, 2018GBP (£)	Jan. 31, 2018GBP (£)
Other Commitment, Fiscal Year Maturity
Operating expense		$ 134,055	$ 140,002	$ 139,232
Rent expense		7,900	$ 6,700	$ 5,900
Lloyd's Syndicates
Other Commitment, Fiscal Year Maturity
FAL deposit assets	$ 142,700	$ 142,700
Current lending capacity under revolving credit agreement | £						£ 30,000,000	£ 20,000,000
Interest rate on revolving credit agreement (percent)	3.80%	3.80%			3.80%
Unused commitments	$ 9,100	$ 9,100			£ 7,100,000
Funding commitments
Other Commitments [Line Items]
Funding commitments related to non-public investment entities	297,800	297,800
Qualified affordable housing project
Other Commitment, Fiscal Year Maturity
Qualified affordable housing project funding commitments	1,000	1,000
Qualified affordable housing project funding commitments, due in 2019	200	200
Qualified affordable housing project funding commitments, due in 2020 and 2021	300	300
Qualified affordable housing project funding commitments, due in 2022 and 2023	400	400
Qualified affordable housing project funding commitments, due thereafter	100	100
Commitment to provide capital | Lloyd's Syndicates
Other Commitments [Line Items]
Funding commitments related to non-public investment entities	$ 200,000	200,000
Data analytics services
Other Commitment, Fiscal Year Maturity
Period of long-term purchase commitment	2 years
Contractual obligation, due in next year	$ 4,800	4,800
Operating expense	1,000
Contractual obligation	$ 8,600	$ 8,600

Commitments and Contingencies_2

Commitments and Contingencies - Operating Leases (Details) $ in Thousands	Dec. 31, 2018USD ($)
Schedule of future minimum lease payments for operating leases
2,019	$ 4,829
2,020	4,020
2,021	3,557
2,022	2,618
2,023	1,888
Thereafter	10,212
Total minimum lease payments	$ 27,124

Debt - Schedule of Debt (Detail

Debt - Schedule of Debt (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Gross debt	$ 289,064	$ 413,460
Less debt issuance costs	1,307	1,649
Debt less debt issuance costs	287,757	411,811
Senior Notes | Senior notes due 2023
Debt Instrument [Line Items]
Gross debt	$ 250,000	250,000
Interest rate	5.30%
Line of Credit | Revolving Credit Agreement
Debt Instrument [Line Items]
Gross debt	$ 0	$ 123,000
Weighted average interest rate		1.91%
Mortgage Loans
Debt Instrument [Line Items]
Gross debt	$ 39,064	$ 40,460
Mortgage Loans | Three month LIBOR
Debt Instrument [Line Items]
Interest rate	4.10%	2.86%
Basis spread on variable rate for debt	1.325%	1.325%

Debt - Narrative (Details)

Debt - Narrative (Details)	12 Months Ended
	Dec. 31, 2018USD ($)lender	Dec. 31, 2017USD ($)
Debt Instrument [Line Items]
Number of participating lenders | lender	7
Interest Rate Cap
Debt Instrument [Line Items]
Floor interest rate on derivative		2.35%
Other assets | Interest Rate Cap
Debt Instrument [Line Items]
Derivative asset, notional amount	$ 35,000,000	$ 35,000,000
Senior Notes | Senior notes due 2023 | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate for debt	0.40%
Line of Credit | Revolving Credit Agreement
Debt Instrument [Line Items]
Current revolving credit capacity	$ 250,000,000
Additional borrowing capacity	$ 50,000,000
Maximum allowable consolidated funded indebtedness ratio (percent)	0.35
Minimum net worth required	$ 1,300,000,000
Line of Credit | Revolving Credit Agreement | Federal Funds Rate
Debt Instrument [Line Items]
Basis spread on variable rate for debt	0.50%
Line of Credit | Revolving Credit Agreement | One month LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate for debt	1.00%
Line of Credit | Revolving Credit Agreement | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate for debt	0.00%
Commitment fee percentages (percent)	0.125%
Line of Credit | Revolving Credit Agreement | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate for debt	1.63%
Commitment fee percentages (percent)	0.25%
Mortgage Loans
Debt Instrument [Line Items]
Maximum allowable consolidated funded indebtedness ratio (percent)	0.35
Debt instrument term		10 years
Debt gross amount	$ 39,064,000	$ 40,500,000
Mortgage Loans | Three month LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate for debt	1.325%	1.325%

Debt - Schedule of Contractual

Debt - Schedule of Contractual Maturities of Mortgage Loans (Details) - Mortgage Loans - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
2,019	$ 1,448
2,020	1,503
2,021	1,559
2,022	1,617
2,023	1,677
Thereafter	31,260
Total principal payments	$ 39,064	$ 40,500

Derivatives - Narrative (Detail

Derivatives - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Mortgage Loans | Three month 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 V

Derivatives - Volume and Fair Value (Details) - Interest Rate Cap - Other assets $ in Thousands	Dec. 31, 2018USD ($)derivative_instrument	Dec. 31, 2017USD ($)derivative_instrument
Derivative [Line Items]
Number of Instruments | derivative_instrument	1	1
Notional Amount	$ 35,000	$ 35,000
Estimated Fair Value	$ 1,884	$ 1,731

Derivatives - Pre-tax Impact of

Derivatives - Pre-tax Impact of Change in Fair Value (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Interest Rate Cap | Interest expense
Derivative [Line Items]
Gains (Losses) Recognized in Income on Derivatives	$ 153	$ (339)	$ 0

Shareholders' Equity - Narrativ

Shareholders' Equity - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity [Abstract]
Common shares authorized (shares)	100,000,000	100,000,000
Authorized preferred stock (shares)	50,000,000	50,000,000
Authorization common shares for the issuance under incentive compensation plans (shares)	2,000,000
Number of shares available for grant (shares)	600,000
Dividends declared	$ 94,300	$ 316,900	$ 315,000
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity attributable to parent	1,523,002	1,594,795	1,798,702	$ 1,958,354
Total authorizations which remain available for use	109,600
Loss related to unrecognized changes in defined benefit plan liabilities			1,000
Impairment losses in accumulated other comprehensive income	100	500
Retained earnings, unappropriated
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity attributable to parent	165,300
Accumulated Other Comprehensive Income (Loss)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity attributable to parent	(16,911)	$ 14,911	$ 17,399	$ 23,855
Tax Cuts and Jobs Act of 2017, reclassification	$ 3,400

Shareholders' Equity - Changes

Shareholders' Equity - Changes in Common Shares (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Dividends Payable [Line Items]
Cash Dividends Declared, per Share	$ 0.81	$ 0.31	$ 0.31	$ 0.310	$ 5	$ 0.31	$ 0.31	$ 0.31	$ 5	$ 0.31	$ 0.31	$ 0.31	$ 1.74	$ 5.93	$ 5.93
Common Stock Outstanding Rollforward [Roll Forward]
Beginning Balance (shares)				53,457				53,251				53,101	53,457	53,251	53,101
Repurchase of shares (shares)													0	0	(44)
Cost of common shares reacquired															$ 2,106
Shares issued due to exercise of options and vesting of share-based compensation awards (shares)													135	132	108
Other shares issued for compensation and shares reissued to stock purchase plan (shares)													45	74	86
Ending Balance (shares)	53,637				53,457				53,251				53,637	53,457	53,251
Special Dividends
Dividends Payable [Line Items]
Cash Dividends Declared, per Share	$ 0.5				$ 4.69				$ 4.69

Shareholders' Equity - Cash Div

Shareholders' Equity - Cash Dividends Declared (Details) - $ / shares	3 Months Ended												12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Cash Dividends Declared, per Share	$ 0.81	$ 0.31	$ 0.31	$ 0.310	$ 5	$ 0.31	$ 0.31	$ 0.31	$ 5	$ 0.31	$ 0.31	$ 0.31	$ 1.74	$ 5.93	$ 5.93
Special Dividends
Class of Stock [Line Items]
Cash Dividends Declared, per Share	$ 0.5				$ 4.69				$ 4.69

Shareholders' Equity - Reclassi

Shareholders' Equity - Reclassifications from AOCI to Net Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reclassification adjustments related to available-for-sale securities
Total gains (losses) reclassified, before-tax effect	$ (347)	$ 2,509	$ (2,724)
Tax effect	73	(878)	953
Net reclassification adjustments	(274)	1,631	(1,771)
Deferred tax expense (benefit) included in OCI	(9,573)	(4,676)	(3,078)
Realized investment gains (losses)
Reclassification adjustments related to available-for-sale securities
Total gains (losses) reclassified, before-tax effect	274	2,512	2,417
Non-credit impairment losses reclassified to earnings, due to sale of securities or reclassification as a credit loss
Reclassification adjustments related to available-for-sale securities
Total gains (losses) reclassified, before-tax effect	(621)	(3)	(3,641)
Unrecognized losses in defined benefit plan liabilities reclassified to earnings, due to the termination and settlement of the plan
Reclassification adjustments related to available-for-sale securities
Total gains (losses) reclassified, before-tax effect	$ 0	$ 0	$ (1,500)

Share-Based Payments - Narrativ

Share-Based Payments - Narrative (Details)	12 Months Ended
	Dec. 31, 2018USD ($)award_typeshares	Dec. 31, 2017USD ($)award_typeshares	Dec. 31, 2016USD ($)award_typeshares	Dec. 31, 2015shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of award types (in award types) | award_type	3	3	3
The aggregate grant date intrinsic value of options exercised	$ 0	$ 0	$ 100,000
Outstanding options (in shares) | shares	0	0	0	2,144
Cash proceeds from stock option exercises			$ 0
Restricted Share Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected average period (years)	3 years
Aggregate grant date fair value	$ 3,600,000	$ 2,200,000	1,800,000
Aggregate intrinsic value	4,100,000	3,100,000	2,100,000
Performance Share Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate grant date fair value	4,500,000	6,100,000	6,200,000
Aggregate intrinsic value	$ 5,000,000	$ 8,700,000	$ 6,900,000
The percentage of award vest (percent)	125.00%	119.00%	98.00%
Performance Share Units | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
The percentage of award vest (percent)	50.00%
Performance Share Units | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
The percentage of award vest (percent)	200.00%
Purchase Match Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected average period (years)	3 years
Aggregate grant date fair value	$ 1,100,000	$ 1,000,000	$ 900,000
Aggregate intrinsic value	1,100,000	$ 1,400,000	$ 1,200,000
Annual contribution for the purchase of shares	$ 5,000

Share-Based Payments - Compensa

Share-Based Payments - Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Summary of compensation expense and related tax benefit recognized during each period and compensation cost expense in future periods
Total share-based compensation expense	$ 5,321	$ 10,615	$ 12,455
Tax benefit recognized	1,100	$ 3,700	$ 4,400
Unrecognized Compensation Cost, amount	$ 5,900
Unrecognized Compensation Cost, remaining recognition period	1 year 6 months

Share-Based Payments - Restrict

Share-Based Payments - Restricted Share Units (Details) - Restricted Share Units - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Summary Activity for restricted share units, number of shares
Beginning balance (in shares)	269,520	240,149	178,468
Granted (in shares)	85,797	84,565	109,181
Forfeited (in shares)	(3,878)	(4,087)	(5,954)
Vested (in shares)	(84,116)	(51,107)	(41,546)
Ending balance (in shares)	267,323	269,520	240,149
Summary Activity for restricted share units, weighted average grant date fair value
Beginning balance (USD per share)	$ 48.63	$ 44.07	$ 43.13
Granted (USD per share)	44.73	58.35	45.59
Forfeited (USD per share)	50.07	52.35	43.99
Vested and released (USD per share)	42.90	43.01	44.04
Ending balance (USD per share)	$ 49.16	$ 48.63	$ 44.07

Share-Based Payments - Performa

Share-Based Payments - Performance Share Units (Details) - Performance Share Units - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Summary Activity for restricted share units, number of shares
Beginning balance (in shares)	212,105	305,240	390,350
Granted (in shares)	27,202	48,000	60,000
Forfeited (in shares)	0	(227)	(5,162)
Vested (in shares)	(104,105)	(140,908)	(139,948)
Ending balance (in shares)	135,202	212,105	305,240
Summary Activity for restricted share units, weighted average grant date fair value
Beginning balance (USD per share)	$ 47.11	$ 43.41	$ 44.65
Granted (USD per share)	44.73	58.35	45.59
Forfeited (USD per share)	0	42.79	43.02
Vested and released (USD per share)	42.79	42.95	44.05
Ending balance (USD per share)	$ 49.95	$ 47.11	$ 43.41

Share-Based Payments - Purchase

Share-Based Payments - Purchase Match Units (Details) - Purchase Match Units - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Summary Activity for restricted share units, number of shares
Beginning balance (in shares)	70,292	72,615	74,483
Granted (in shares)	0	24,444	23,903
Forfeited (in shares)	(1,594)	(2,012)	(2,875)
Vested (in shares)	(24,016)	(24,755)	(22,896)
Ending balance (in shares)	44,682	70,292	72,615
Summary Activity for restricted share units, weighted average grant date fair value
Beginning balance (USD per share)	$ 49.40	$ 45.77	$ 42.80
Granted (USD per share)	0	51.83	50.18
Forfeited (USD per share)	50.19	48.29	43.77
Vested and released (USD per share)	46.28	41.33	40.88
Ending balance (USD per share)	$ 51.05	$ 49.40	$ 45.77

Share-Based Payments - Stock Op

Share-Based Payments - Stock Options (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Summary of activity for stock options
Beginning balance (in shares)	0	0	2,144
Exercised (in shares)	0	0	(2,144)
Ending balance (in shares)	0	0	0
Summary of activity for stock options, weighted average exercise price
Beginning balance (USD per share)	$ 0	$ 0	$ 25.02
Exercised (USD per share)	0	0	25.02
Ending balance (USD per share)	$ 0	$ 0	$ 0

Variable Interest Entities (Det

Variable Interest Entities (Details) - Variable interest entity, not primary beneficiary - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Investment in unconsolidated subsidiaries
Variable Interest Entity [Line Items]
Variable interest entity nonconsolidated assets	$ 285.8
Other investments
Variable Interest Entity [Line Items]
Variable interest entity nonconsolidated assets		$ 33.9
Equity Method Investments
Variable Interest Entity [Line Items]
Variable interest entity nonconsolidated assets		$ 269

Earnings Per Share (Details)

Earnings Per Share (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Weighted average number of common shares outstanding, basic (shares)	53,598,000	53,393,000	53,216,000
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average number of common shares outstanding, diluted (shares)	53,749,000	53,611,000	53,448,000
Effect of dilutive shares on earnings per share (USD per share)	$ 0	$ (0.01)	$ (0.01)
Antidilutive shares excluded from computation of earnings per share (in shares)	2,000	7,000	0
Restricted Share Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dilutive securities (shares)	70,000	85,000	73,000
Performance Share Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dilutive securities (shares)	63,000	110,000	135,000
Purchase Match Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dilutive securities (shares)	18,000	23,000	24,000

Segment Information - Narrative

Segment Information - Narrative (Details)	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Syndicate 1,729
Segment Reporting Information [Line Items]
Proportion of capital provided to support Lloyd's syndicate (percent)		62.00%	58.00%
Workers' Compensation Insurance
Segment Reporting Information [Line Items]
Alternative market solutions percentage ceded	100.00%
Syndicate 6,131
Segment Reporting Information [Line Items]
Proportion of capital provided to support Lloyd's syndicate (percent)		100.00%

Segment Information - Financial

Segment Information - Financial Data by Segment (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Net premiums earned	$ 202,033,000	$ 206,070,000	$ 223,591,000	$ 187,159,000	$ 182,972,000	$ 192,303,000	$ 180,353,000	$ 182,903,000	$ 818,853,000	$ 738,531,000	$ 733,281,000
Net investment income									91,884,000	95,662,000	100,012,000
Equity in earnings (loss) of unconsolidated subsidiaries									8,948,000	8,033,000	(5,762,000)
Net realized gains (losses)									(43,488,000)	16,409,000	34,875,000
Other income									9,833,000	7,514,000	7,808,000
Net losses and loss adjustment expenses									(593,210,000)	(469,158,000)	(443,229,000)
Underwriting, policy acquisition and operating expenses									(238,556,000)	(235,753,000)	(227,610,000)
Segregated portfolio cells dividend (expense) income									(9,122,000)	(15,771,000)	(8,142,000)
Interest expense									(16,117,000)	(16,844,000)	(15,032,000)
Income tax benefit (expense)									18,032,000	(21,359,000)	(25,120,000)
Segment operating results	$ (24,450,000)	$ 31,228,000	$ 28,423,000	$ 11,856,000	$ 17,342,000	$ 28,949,000	19,518,000	$ 41,455,000	47,057,000	107,264,000	151,081,000
Depreciation and amortization, net of accretion									21,255,000	28,796,000	32,789,000
Specialty P&C
Segment Reporting Information [Line Items]
Net premiums earned									491,787,000	449,823,000	454,506,000
Workers' Compensation Insurance
Segment Reporting Information [Line Items]
Net premiums earned									186,079,000	163,309,000	161,988,000
Segregated Portfolio Cell Reinsurance
Segment Reporting Information [Line Items]
Net premiums earned									73,940,000	68,197,000	62,137,000
Lloyd's Syndicates
Segment Reporting Information [Line Items]
Net premiums earned									67,047,000	57,202,000	54,650,000
Operating segments | Specialty P&C
Segment Reporting Information [Line Items]
Net premiums earned									491,787,000	449,823,000	454,506,000
Net investment income									0	0	0
Equity in earnings (loss) of unconsolidated subsidiaries									0	0	0
Net realized gains (losses)									0	0	0
Other income									5,844,000	5,688,000	5,306,000
Net losses and loss adjustment expenses									(384,431,000)	(285,250,000)	(266,090,000)
Underwriting, policy acquisition and operating expenses									(112,419,000)	(107,972,000)	(103,656,000)
Segregated portfolio cells dividend (expense) income									0	(5,181,000)	0
Interest expense									0	0	0
Income tax benefit (expense)									0	0	0
Segment operating results									781,000	57,108,000	90,066,000
Depreciation and amortization, net of accretion									7,050,000	7,922,000	7,268,000
Operating segments | Specialty P&C | Previously Unrecognized Segregated Portfolio Cells (SPC) Dividend Expense
Segment Reporting Information [Line Items]
Dividend expense							5,200,000
Operating segments | Workers' Compensation Insurance
Segment Reporting Information [Line Items]
Net premiums earned									186,079,000	163,309,000	161,988,000
Net investment income									0	0	0
Equity in earnings (loss) of unconsolidated subsidiaries									0	0	0
Net realized gains (losses)									0	0	0
Other income									2,412,000	2,096,000	2,218,000
Net losses and loss adjustment expenses									(118,483,000)	(102,233,000)	(107,791,000)
Underwriting, policy acquisition and operating expenses									(55,693,000)	(52,576,000)	(53,597,000)
Segregated portfolio cells dividend (expense) income									0	0	0
Interest expense									0	0	0
Income tax benefit (expense)									0	0	0
Segment operating results									14,315,000	10,596,000	2,818,000
Depreciation and amortization, net of accretion									3,850,000	3,480,000	5,600,000
Operating segments | Segregated Portfolio Cell Reinsurance
Segment Reporting Information [Line Items]
Net premiums earned									73,940,000	68,197,000	62,137,000
Net investment income									1,566,000	1,059,000	711,000
Equity in earnings (loss) of unconsolidated subsidiaries									0	0	0
Net realized gains (losses)									(3,149,000)	3,914,000	2,525,000
Other income									211,000	115,000	18,000
Net losses and loss adjustment expenses									(38,726,000)	(37,455,000)	(35,232,000)
Underwriting, policy acquisition and operating expenses									(22,426,000)	(20,764,000)	(18,936,000)
Segregated portfolio cells dividend (expense) income									(9,122,000)	(10,590,000)	(8,142,000)
Interest expense									0	0	0
Income tax benefit (expense)									0	0	0
Segment operating results									2,294,000	4,476,000	3,081,000
Depreciation and amortization, net of accretion									441,000	680,000	595,000
Operating segments | Lloyd's Syndicates
Segment Reporting Information [Line Items]
Net premiums earned									67,047,000	57,202,000	54,650,000
Net investment income									3,358,000	1,736,000	1,410,000
Equity in earnings (loss) of unconsolidated subsidiaries									0	0	0
Net realized gains (losses)									(460,000)	107,000	76,000
Other income									322,000	(1,476,000)	1,415,000
Net losses and loss adjustment expenses									(51,570,000)	(44,220,000)	(34,116,000)
Underwriting, policy acquisition and operating expenses									(31,686,000)	(26,963,000)	(22,832,000)
Segregated portfolio cells dividend (expense) income									0	0	0
Interest expense									0	0	0
Income tax benefit (expense)									317,000	568,000	(384,000)
Segment operating results									(12,672,000)	(13,046,000)	219,000
Depreciation and amortization, net of accretion									(8,000)	(20,000)	132,000
Operating segments | Corporate
Segment Reporting Information [Line Items]
Net premiums earned									0	0	0
Net investment income									86,960,000	92,867,000	97,891,000
Equity in earnings (loss) of unconsolidated subsidiaries									8,948,000	8,033,000	(5,762,000)
Net realized gains (losses)									(39,879,000)	12,388,000	32,274,000
Other income									3,525,000	2,888,000	1,069,000
Net losses and loss adjustment expenses									0	0	0
Underwriting, policy acquisition and operating expenses									(18,767,000)	(29,275,000)	(30,807,000)
Segregated portfolio cells dividend (expense) income									0	0	0
Interest expense									(16,163,000)	(16,844,000)	(15,032,000)
Income tax benefit (expense)									17,715,000	(21,927,000)	(24,736,000)
Segment operating results									42,339,000	48,130,000	54,897,000
Depreciation and amortization, net of accretion									9,922,000	16,734,000	19,194,000
Operating segments | Corporate | Previously Unrecognized Segregated Portfolio Cells (SPC) Dividend Expense
Segment Reporting Information [Line Items]
Income tax benefit (expense)							$ 1,800
Inter-segment Eliminations
Segment Reporting Information [Line Items]
Net premiums earned									0	0	0
Net investment income									0	0	0
Equity in earnings (loss) of unconsolidated subsidiaries									0	0	0
Net realized gains (losses)									0	0	0
Other income									(2,481,000)	(1,797,000)	(2,218,000)
Net losses and loss adjustment expenses									0	0	0
Underwriting, policy acquisition and operating expenses									2,435,000	1,797,000	2,218,000
Segregated portfolio cells dividend (expense) income									0	0	0
Interest expense									46,000	0	0
Income tax benefit (expense)									0	0	0
Segment operating results									0	0	0
Depreciation and amortization, net of accretion									$ 0	$ 0	$ 0

Segment Information - Gross Pre

Segment Information - Gross Premiums Earned by Product (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Premiums ceded									$ (126,036)	$ (110,347)	$ (95,315)
Net premiums earned	$ 202,033	$ 206,070	$ 223,591	$ 187,159	$ 182,972	$ 192,303	$ 180,353	$ 182,903	818,853	738,531	733,281
Specialty P&C
Segment Reporting Information [Line Items]
Premiums ceded									(88,235)	(87,760)	(81,425)
Net premiums earned									491,787	449,823	454,506
Premiums assumed											14,000
Specialty P&C | Healthcare professional liability
Segment Reporting Information [Line Items]
Gross premiums earned									518,303	477,561	474,981
Specialty P&C | Legal professional liability
Segment Reporting Information [Line Items]
Gross premiums earned									26,094	25,771	26,125
Specialty P&C | Medical technology liability
Segment Reporting Information [Line Items]
Gross premiums earned									35,157	33,836	34,158
Specialty P&C | Other
Segment Reporting Information [Line Items]
Gross premiums earned									468	415	667
Workers' Compensation Insurance
Segment Reporting Information [Line Items]
Premiums ceded									(96,895)	(90,635)	(85,104)
Net premiums earned									186,079	163,309	161,988
Workers' Compensation Insurance | Traditional business
Segment Reporting Information [Line Items]
Gross premiums earned									199,466	173,246	171,434
Workers' Compensation Insurance | Alternative market business
Segment Reporting Information [Line Items]
Gross premiums earned									83,508	80,698	75,658
Segregated Portfolio Cell Reinsurance
Segment Reporting Information [Line Items]
Premiums ceded									(9,324)	(8,714)	(8,072)
Net premiums earned									73,940	68,197	62,137
Segregated Portfolio Cell Reinsurance | Healthcare professional liability
Segment Reporting Information [Line Items]
Gross premiums earned									5,009	4,097	3,310
Segregated Portfolio Cell Reinsurance | Alternative market business
Segment Reporting Information [Line Items]
Gross premiums earned									78,255	72,814	66,899
Lloyd's Syndicates
Segment Reporting Information [Line Items]
Gross premiums earned									83,307	69,749	60,564
Premiums ceded									(16,260)	(12,547)	(5,914)
Net premiums earned									$ 67,047	$ 57,202	$ 54,650

Benefit Plans (Details)

Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Contribution Plan Disclosure [Line Items]
Incurred expense related to savings and retirement plans	$ 7	$ 7.8	$ 6.9
Incurred expense related to non qualified deferred compensation plans	0.3	0.3
ProAssurance deferred compensation liabilities total	$ 21.3	$ 20.5
Maximum
Defined Contribution Plan Disclosure [Line Items]
Percentage of benefit plan contribution by employer (percent)	10.00%

Statutory Accounting and Divi_3

Statutory Accounting and Dividend Restrictions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Consolidated Net Income Related to Statutory Accounting
Statutory Net Earnings	$ 135	$ 139	$ 163
Statutory Capital and Surplus	1,041	$ 1,175
Net assets held at domestic insurance subsidiaries	1,300
Statutory dividend payments permitted from insurance subsidiaries	$ 128

Quarterly Results of Operatio_3

Quarterly Results of Operations (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Data [Abstract]
Net premiums earned	$ 202,033	$ 206,070	$ 223,591	$ 187,159	$ 182,972	$ 192,303	$ 180,353	$ 182,903	$ 818,853	$ 738,531	$ 733,281
Net losses and loss adjustment expenses:
Current year	179,056	169,154	184,543	152,572	149,399	161,631	144,562	147,927	685,326	603,518	587,007
Favorable development of reserves established in prior years, net	(24,967)	(21,549)	(22,815)	(22,786)	(44,297)	(32,275)	(29,012)	(28,776)	(92,116)	(134,360)	(143,778)
Net income (loss)	$ (24,450)	$ 31,228	$ 28,423	$ 11,856	$ 17,342	$ 28,949	$ 19,518	$ 41,455	$ 47,057	$ 107,264	$ 151,081
Basic earnings per share (USD per share)	$ (0.46)	$ 0.58	$ 0.53	$ 0.22	$ 0.32	$ 0.54	$ 0.37	$ 0.78	$ 0.88	$ 2.01	$ 2.84
Diluted earnings per share (USD per share)	$ (0.46)	$ 0.58	$ 0.53	$ 0.22	$ 0.32	$ 0.54	$ 0.36	$ 0.77	$ 0.88	$ 2	$ 2.83

Schedule I - Summary of Inves_2

Schedule I - Summary of Investments - Other Than Investments In Related Parties (Details) $ in Thousands	Dec. 31, 2018USD ($)
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	$ 3,267,222
Fair Value	3,349,382
Amount Which is Presented in the Balance Sheet	3,349,382
U.S. Government or government agencies and authorities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	171,770
Fair Value	170,154
Amount Which is Presented in the Balance Sheet	170,154
State and municipal bonds
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	289,544
Fair Value	293,772
Amount Which is Presented in the Balance Sheet	293,772
Foreign governments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	30,318
Fair Value	29,892
Amount Which is Presented in the Balance Sheet	29,892
Public utilities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	76,735
Fair Value	76,059
Amount Which is Presented in the Balance Sheet	76,059
All other corporate bonds
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	1,160,474
Fair Value	1,140,356
Amount Which is Presented in the Balance Sheet	1,140,356
Certificates of deposit
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	100
Fair Value	100
Amount Which is Presented in the Balance Sheet	100
Mortgage-backed securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	426,329
Fair Value	421,653
Amount Which is Presented in the Balance Sheet	421,653
Total Fixed Maturities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	2,155,270
Fair Value	2,131,986
Amount Which is Presented in the Balance Sheet	2,131,986
Public utilities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	7,553
Fair Value	9,177
Amount Which is Presented in the Balance Sheet	9,177
Banks, trusts and insurance companies
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	64,148
Fair Value	62,344
Amount Which is Presented in the Balance Sheet	62,344
Industrial, miscellaneous and all other
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	379,230
Fair Value	371,416
Amount Which is Presented in the Balance Sheet	371,416
Equity Securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	450,931
Fair Value	442,937
Amount Which is Presented in the Balance Sheet	442,937
Other long-term investments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	352,654
Fair Value	466,140
Amount Which is Presented in the Balance Sheet	466,140
Short-term investments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Recorded Cost Basis	308,367
Fair Value	308,319
Amount Which is Presented in the Balance Sheet	$ 308,319

Schedule II - Condensed Finan_2

Schedule II - Condensed Financial Information of Registrant - Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assets
Fixed maturities available for sale, at fair value	$ 2,093,798	$ 2,280,242
Short-term investments	308,319	432,126
Cash and cash equivalents	80,471	134,495	$ 117,347	$ 241,100
Other assets	111,559	101,428
Total Assets	4,600,726	4,929,197
Liabilities
Dividends declared and not yet paid	43,446	267,292	265,659
Other liabilities	199,295	437,600
Total Liabilities	3,077,724	3,334,402
Shareholders’ Equity:
Common stock	630	628
Total Shareholders’ Equity	1,523,002	1,594,795	1,798,702	1,958,354
Total Liabilities and Shareholders' Equity	4,600,726	4,929,197
Parent Company
Assets
Investment in subsidiaries, at equity	1,599,486	1,713,656
Fixed maturities available for sale, at fair value	78,076	155,094
Short-term investments	76,347	268,181
Investment in unconsolidated subsidiaries	875	1,200
Cash and cash equivalents	25,757	81,009	31,330	$ 103,292
Due from subsidiaries	0	2,666
Other assets	45,683	33,829
Total Assets	1,826,224	2,255,635
Liabilities
Due to subsidiaries	4,067	0
Dividends declared and not yet paid	43,446	267,292	$ 265,659
Other liabilities	6,823	22,008
Debt less debt issuance costs	248,886	371,540
Total Liabilities	303,222	660,840
Shareholders’ Equity:
Common stock	630	628
Other shareholders’ equity, including unrealized gains (losses) on securities of subsidiaries	1,522,372	1,594,167
Total Shareholders’ Equity	1,523,002	1,594,795
Total Liabilities and Shareholders' Equity	$ 1,826,224	$ 2,255,635

Schedule II - Condensed Finan_3

Schedule II - Condensed Financial Information of Registrant - Statements of Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues
Net investment income									$ 91,884	$ 95,662	$ 100,012
Equity in earnings (loss) of unconsolidated subsidiaries									8,948	8,033	(5,762)
Net realized investment gains (losses)									(43,488)	16,409	34,875
Other income									9,833	7,514	7,808
Total revenues									886,030	866,149	870,214
Expenses
Interest expense									16,117	16,844	15,032
Total expenses									857,005	737,526	694,013
Income tax expense (benefit)									(18,032)	21,359	25,120
Segment operating results	$ (24,450)	$ 31,228	$ 28,423	$ 11,856	$ 17,342	$ 28,949	$ 19,518	$ 41,455	47,057	107,264	151,081
Other comprehensive income (loss)									(35,238)	(2,488)	(6,456)
Comprehensive income (loss)									11,819	104,776	144,625
Parent Company
Revenues
Net investment income									3,495	7,646	6,359
Equity in earnings (loss) of unconsolidated subsidiaries									(325)	(137)	(155)
Net realized investment gains (losses)									(789)	(8,606)	405
Other income									977	921	(960)
Total revenues									3,358	(176)	5,649
Expenses
Interest expense									14,844	16,440	15,030
Other expenses									17,092	26,351	28,305
Total expenses									31,936	42,791	43,335
Income (loss) before income tax expense (benefit) and equity in net income of consolidated subsidiaries									(28,578)	(42,967)	(37,686)
Income tax expense (benefit)									(7,142)	(13,293)	(12,583)
Income (loss) before equity in net income of consolidated subsidiaries									(21,436)	(29,674)	(25,103)
Equity in net income of consolidated subsidiaries									68,493	136,938	176,184
Segment operating results									47,057	107,264	151,081
Other comprehensive income (loss)									(35,238)	(2,488)	(6,456)
Comprehensive income (loss)									$ 11,819	$ 104,776	$ 144,625

Schedule II - Condensed Finan_4

Schedule II - Condensed Financial Information of Registrant - Cash Flow (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided (used) by operating activities	$ 177,265	$ 173,388	$ 178,983
(Investments in) distributions from unconsolidated subsidiaries, net:
Other partnership investments	(32,153)	(50,362)	(18,613)
Proceeds from sales or maturities of:
Fixed maturities, available for sale	914,021	932,070	752,516
Net decrease (increase) in short-term investments	123,886	4,167	(322,872)
Unsettled security transactions, net of change	(4,022)	(2,031)	1,388
Other	(1,305)	(2,025)	6,187
Net cash provided (used) by investing activities	214,897	200,275	(288,802)
Financing Activities
Repurchase of common stock	0	0	(2,106)
Dividends to shareholders	(316,476)	(315,228)	(118,812)
Other	(4,309)	(7,683)	(2,968)
Net cash provided (used) by financing activities	(446,186)	(356,515)	(13,934)
Increase (decrease) in cash and cash equivalents	(54,024)	17,148	(123,753)
Cash and cash equivalents at beginning of period	134,495	117,347	241,100
Cash and cash equivalents at end of period	80,471	134,495	117,347
Supplemental Disclosure of Cash Flow Information
Cash paid during the year for interest	16,165	15,892	14,732
Significant non-cash transactions:
Dividends declared and not yet paid	43,446	267,292	265,659
Parent Company
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided (used) by operating activities	27,981	67,779	41,356
(Investments in) distributions from unconsolidated subsidiaries, net:
Other partnership investments	0	0	(1,000)
Proceeds from sales or maturities of:
Fixed maturities, available for sale	169,822	295,035	100,240
Net decrease (increase) in short-term investments	194,035	11,811	(262,169)
Dividends from subsidiaries	29,395	99,694	70,125
Contribution of capital to subsidiaries	0	0	(1,983)
Unsettled security transactions, net of change	0	1,100	(1,100)
Funds (advanced) repaid for Lloyd's FAL deposit	(21,576)	(25,449)	0
Funds (advanced) repaid under Syndicate Credit Agreement	(11,232)	(6,883)	1,695
Funds (advanced) repaid under a business investment line of credit	0	(4,066)	(3,090)
Other	330	(2,276)	(2,805)
Net cash provided (used) by investing activities	360,774	368,966	(100,087)
Financing Activities
Borrowings (repayments) under Revolving Credit Agreement	(123,000)	(77,000)	100,000
Repurchase of common stock	0	0	(2,106)
Subsidiary payments for common shares and share-based compensation awarded to subsidiary employees	1,154	12,030	11,384
Dividends to shareholders	(316,476)	(315,228)	(118,812)
Other	(5,685)	(6,868)	(3,697)
Net cash provided (used) by financing activities	(444,007)	(387,066)	(13,231)
Increase (decrease) in cash and cash equivalents	(55,252)	49,679	(71,962)
Cash and cash equivalents at beginning of period	81,009	31,330	103,292
Cash and cash equivalents at end of period	25,757	81,009	31,330
Supplemental Disclosure of Cash Flow Information
Cash paid during the year for income taxes, net of refunds	4,966	17,193	(8,519)
Cash paid during the year for interest	14,777	15,892	14,732
Significant non-cash transactions:
Dividends declared and not yet paid	43,446	267,292	265,659
Securities transferred at fair value as dividends from subsidiaries	$ 98,292	$ 190,709	$ 174,270

Schedule II - Condensed Finan_5

Schedule II - Condensed Financial Information of Registrant - Notes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Return of invested capital from unconsolidated subsidiaries	$ 84,534	$ 32,539	$ 7,084
Accounting Standards Update 2016-15
Condensed Financial Statements, Captions [Line Items]
Return of invested capital from unconsolidated subsidiaries		$ 24,400	$ 9,900

Schedule III - Supplementary _2

Schedule III - Supplementary Insurance Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Net premiums earned									$ 818,853	$ 738,531	$ 733,281
Net investment income									91,884	95,662	100,012
Losses and loss adjustment expenses incurred related to current year, net of reinsurance	$ 179,056	$ 169,154	$ 184,543	$ 152,572	$ 149,399	$ 161,631	$ 144,562	$ 147,927	685,326	603,518	587,007
Losses and loss adjustment expenses incurred related to prior year, net of reinsurance	(24,967)	$ (21,549)	$ (22,815)	$ (22,786)	(44,297)	$ (32,275)	$ (29,012)	$ (28,776)	(92,116)	(134,360)	(143,778)
Paid losses and loss adjustment expenses, net of reinsurance									529,979	476,315	479,252
Underwriting, policy acquisition and operating expenses:									104,501	95,751	88,378
Other underwriting, policy acquisition and operating expenses									134,055	140,002	139,232
Net premiums written									834,914	764,018	738,533
Deferred policy acquisition costs	54,116				50,261				54,116	50,261	46,809
Reserve for losses and loss adjustment expenses	2,119,847				2,048,381				2,119,847	2,048,381	1,993,428
Unearned premiums	$ 415,211				$ 398,884				415,211	398,884	372,563
Specialty P&C
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Net premiums earned									491,787	449,823	454,506
Losses and loss adjustment expenses incurred related to prior year, net of reinsurance									(77,085)	(119,293)	(137,159)
Net premiums written									494,148	466,621	454,718
Workers' Compensation Insurance
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Net premiums earned									186,079	163,309	161,988
Losses and loss adjustment expenses incurred related to prior year, net of reinsurance									(8,051)	(5,742)	(1,551)
Net premiums written									195,350	173,566	163,513
Segregated Portfolio Cell Reinsurance
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Net premiums earned									73,940	68,197	62,137
Net investment income									1,566	1,059	711
Losses and loss adjustment expenses incurred related to prior year, net of reinsurance									(8,967)	(8,513)	(4,569)
Net premiums written									75,547	68,862	64,028
Lloyd's Syndicates
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Net premiums earned									67,047	57,202	54,650
Net investment income									3,358	1,736	1,410
Losses and loss adjustment expenses incurred related to prior year, net of reinsurance									1,987	(812)	(499)
Net premiums written									69,869	54,969	56,274
Corporate
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Net investment income									86,960	92,867	97,891
Operating segments | Specialty P&C
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Losses and loss adjustment expenses incurred related to current year, net of reinsurance									461,516	404,543	403,249
Paid losses and loss adjustment expenses, net of reinsurance									354,221	320,776	341,189
Underwriting, policy acquisition and operating expenses:									52,253	47,615	44,344
Other underwriting, policy acquisition and operating expenses									60,166	60,357	59,312
Operating segments | Workers' Compensation Insurance
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Losses and loss adjustment expenses incurred related to current year, net of reinsurance									126,534	107,975	109,342
Paid losses and loss adjustment expenses, net of reinsurance									108,742	96,734	89,418
Underwriting, policy acquisition and operating expenses:									16,864	14,551	13,273
Other underwriting, policy acquisition and operating expenses									38,829	38,025	40,324
Operating segments | Segregated Portfolio Cell Reinsurance
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Losses and loss adjustment expenses incurred related to current year, net of reinsurance									47,693	45,968	39,801
Paid losses and loss adjustment expenses, net of reinsurance									29,320	28,761	27,391
Underwriting, policy acquisition and operating expenses:									21,039	19,927	18,385
Other underwriting, policy acquisition and operating expenses									1,387	837	551
Operating segments | Lloyd's Syndicates
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Losses and loss adjustment expenses incurred related to current year, net of reinsurance									49,583	45,032	34,615
Paid losses and loss adjustment expenses, net of reinsurance									37,496	29,926	21,254
Underwriting, policy acquisition and operating expenses:									15,913	15,194	13,769
Other underwriting, policy acquisition and operating expenses									15,773	11,769	9,063
Operating segments | Corporate
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Other underwriting, policy acquisition and operating expenses									18,767	29,275	30,807
Inter-segment Eliminations
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Paid losses and loss adjustment expenses, net of reinsurance									200	118	0
Underwriting, policy acquisition and operating expenses:									(1,568)	(1,536)	(1,393)
Other underwriting, policy acquisition and operating expenses									$ (867)	$ (261)	$ (825)

Schedule IV - Reinsurance (Deta

Schedule IV - Reinsurance (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property and Liability
Premiums earned									$ 903,354	$ 821,249	$ 790,791
Premiums ceded									(126,036)	(110,347)	(95,315)
Premiums assumed									41,535	27,629	37,805
Net premiums earned	$ 202,033	$ 206,070	$ 223,591	$ 187,159	$ 182,972	$ 192,303	$ 180,353	$ 182,903	$ 818,853	$ 738,531	$ 733,281
Percentage of amount assumed to net									5.07%	3.74%	5.16%