ProAssurance (PRA) 10-Q 3 May 18 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2018	Apr. 30, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	PROASSURANCE CORP
Entity Central Index Key	1,127,703
Document Type	10-Q
Document Period End Date	Mar. 31, 2018
Amendment Flag	false
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		53,593,712

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Investments
Fixed maturities, at fair value; cost or amortized cost, $2,169,546 and $2,257,188, respectively	$ 2,157,831	$ 2,280,242
Equity investments, at fair value; cost, $471,337 and $425,942, respectively	492,159	470,609
Short-term investments	349,119	432,126
Business owned life insurance	62,562	62,113
Investment in unconsolidated subsidiaries	401,030	330,591
Other investments, $33,042 and $52,301 at fair value, respectively, otherwise at cost or amortized cost	35,944	110,847
Total Investments	3,498,645	3,686,528
Cash and cash equivalents	43,247	134,495
Premiums receivable	247,644	238,085
Receivable from reinsurers on paid losses and loss adjustment expenses	12,935	7,317
Receivable from reinsurers on unpaid losses and loss adjustment expenses	329,540	335,585
Prepaid reinsurance premiums	39,899	39,916
Deferred policy acquisition costs	50,765	50,261
Deferred tax asset, net	16,874	9,930
Real estate, net	31,646	31,975
Intangible assets, net	81,408	82,952
Goodwill	210,725	210,725
Other assets	115,596	101,428
Total Assets	4,678,924	4,929,197
Policy liabilities and accruals
Reserve for losses and loss adjustment expenses	2,056,801	2,048,381
Unearned premiums	426,627	398,884
Reinsurance premiums payable	46,933	37,726
Total Policy Liabilities	2,530,361	2,484,991
Other liabilities	207,866	437,600
Debt less debt issuance costs	371,528	411,811
Total Liabilities	3,109,755	3,334,402
Shareholders' Equity
Common shares, par value $0.01 per share, 100,000,000 shares authorized, 62,960,615 and 62,824,523 shares issued, respectively	630	628
Additional paid-in capital	380,250	383,077
Accumulated other comprehensive income (loss), net of deferred tax expense (benefit) of ($1,842) and $5,218, respectively	(8,046)	14,911
Retained earnings	1,614,344	1,614,186
Treasury shares, at cost, 9,367,545 shares and 9,367,502 shares, respectively	(418,009)	(418,007)
Total Shareholders' Equity	1,569,169	1,594,795
Total Liabilities and Shareholders' Equity	$ 4,678,924	$ 4,929,197

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Marketable securities, amortized cost	$ 2,169,546	$ 2,257,188
Equity Investments, fair value, cost	471,337	425,942
Other investments, portion carried at fair value	$ 33,042	$ 52,301
Common shares, par value (USD per share)	$ 0.01	$ 0.01
Common shares, shares authorized (in shares)	100,000,000	100,000,000
Common shares, shares issued (in shares)	62,960,615	62,824,523
Deferred tax expense (benefit) on accumulated other comprehensive income (loss)	$ (1,842)	$ 5,218
Treasury shares, number of shares (in shares)	9,367,545	9,367,502

Condensed Consolidated Statemen

Condensed Consolidated Statements of Changes in Capital (Unaudited) - USD ($)		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Increase (Decrease) in Stockholders' Equity:
Beginning Balance		$ 1,594,795,000	$ 1,798,702,000
Common shares issued for compensation and effect of shares reissued to stock purchase plan		120,000	940,000
Share-based compensation		902,000	3,346,000
Net effect of restricted and performance shares issued		(3,849,000)	(5,314,000)
Dividends to shareholders		(16,616,000)	(16,516,000)
Other comprehensive income (loss)		(26,373,000)	2,924,000
Net income		11,856,000	41,455,000
Ending Balance		1,569,169,000	1,825,686,000
Accounting Standards Update 2016-01
Increase (Decrease) in Stockholders' Equity:
Cumulative-effect adjustment adoption of ASU	[1]			$ 8,334,000
Accounting Standards Update 2016-09
Increase (Decrease) in Stockholders' Equity:
Cumulative-effect adjustment adoption of ASU	[1]				$ 149,000
Common Stock
Increase (Decrease) in Stockholders' Equity:
Beginning Balance		628,000	627,000
Net effect of restricted and performance shares issued		2,000	1,000
Ending Balance		630,000	628,000
Additional Paid-in Capital
Increase (Decrease) in Stockholders' Equity:
Beginning Balance		383,077,000	376,518,000
Common shares issued for compensation and effect of shares reissued to stock purchase plan		122,000	938,000
Share-based compensation		902,000	3,346,000
Net effect of restricted and performance shares issued		(3,851,000)	(5,315,000)
Ending Balance		380,250,000	375,912,000
Additional Paid-in Capital | Accounting Standards Update 2016-09
Increase (Decrease) in Stockholders' Equity:
Cumulative-effect adjustment adoption of ASU	[1]				425,000
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity:
Beginning Balance		14,911,000	17,399,000
Other comprehensive income (loss)		(26,373,000)	2,924,000
Ending Balance		(8,046,000)	20,323,000
Accumulated Other Comprehensive Income (Loss) | Accounting Standards Update 2018-02
Increase (Decrease) in Stockholders' Equity:
Cumulative-effect adjustment adoption of ASU	[1]			3,416,000
Retained Earnings
Increase (Decrease) in Stockholders' Equity:
Beginning Balance		1,614,186,000	1,824,088,000
Dividends to shareholders		(16,616,000)	(16,516,000)
Net income		11,856,000	41,455,000
Ending Balance		1,614,344,000	1,848,751,000
Retained Earnings | Accounting Standards Update 2016-01
Increase (Decrease) in Stockholders' Equity:
Cumulative-effect adjustment adoption of ASU	[1]			8,334,000
Retained Earnings | Accounting Standards Update 2018-02
Increase (Decrease) in Stockholders' Equity:
Cumulative-effect adjustment adoption of ASU	[1]			$ (3,416,000)
Retained Earnings | Accounting Standards Update 2016-09
Increase (Decrease) in Stockholders' Equity:
Cumulative-effect adjustment adoption of ASU	[1]				$ (276,000)
Treasury Stock
Increase (Decrease) in Stockholders' Equity:
Beginning Balance		(418,007,000)	(419,930,000)
Common shares issued for compensation and effect of shares reissued to stock purchase plan		(2,000)	2,000
Ending Balance		$ (418,009,000)	$ (419,928,000)
[1]	See Note 1 for discussion of accounting guidance adopted during the period.

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Income and Comprehensive Income (Unaudited) - USD ($) shares in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues
Net premiums earned	$ 187,159,000	$ 182,903,000
Net investment income	22,027,000	23,186,000
Equity in earnings (loss) of unconsolidated subsidiaries	1,640,000	1,808,000
Net realized investment gains (losses):
OTTI losses	0	(419,000)
Portion of OTTI losses recognized in other comprehensive income before taxes	0	248,000
Net impairment losses recognized in earnings	0	(171,000)
Other net realized investment gains (losses)	(12,517,000)	13,451,000
Total net realized investment gains (losses)	(12,517,000)	13,280,000
Other income	2,723,000	1,821,000
Total revenues	201,032,000	222,998,000
Expenses
Net losses and loss adjustment expenses	129,786,000	119,151,000
Underwriting, policy acquisition and operating expenses
Operating expense	32,467,000	34,482,000
DPAC amortization	24,893,000	22,626,000
Segregated portfolio cells dividend expense (income)	1,747,000	2,375,000
Interest expense	3,705,000	4,133,000
Total expenses	192,598,000	182,767,000
Income before income taxes	8,434,000	40,231,000
Provision for income taxes
Current expense (benefit)	(1,328,000)	(8,278,000)
Deferred expense (benefit)	(2,094,000)	7,054,000
Total income tax expense (benefit)	(3,422,000)	(1,224,000)
Net income	11,856,000	41,455,000
Other comprehensive income (loss), after tax, net of reclassification adjustments	(26,373,000)	2,924,000
Comprehensive income (loss)	$ (14,517,000)	$ 44,379,000
Earnings per share
Basic (USD per share)	$ 0.22	$ 0.78
Diluted (USD per share)	$ 0.22	$ 0.77
Weighted average number of common shares outstanding:
Basic (in shares)	53,515	53,315
Diluted (in shares)	53,682	53,535
Cash dividends declared per common share (USD per share)	$ 0.310	$ 0.31

Condensed Consolidated Stateme6

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating Activities
Net income	$ 11,856,000	$ 41,455,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization, net of accretion	6,079,000	7,803,000
(Increase) decrease in cash surrender value of BOLI	(449,000)	(455,000)
Net realized investment (gains) losses	12,517,000	(13,280,000)
Share-based compensation	902,000	3,346,000
Deferred income taxes	(2,094,000)	7,054,000
Policy acquisition costs, net of amortization (net deferral)	(504,000)	(2,376,000)
Equity in (earnings) loss of unconsolidated subsidiaries	(1,640,000)	(1,808,000)
Distributed earnings from unconsolidated subsidiaries	7,018,000	10,893,000
Other	752,000	(167,000)
Other changes in assets and liabilities:
Premiums receivable	(9,559,000)	(1,238,000)
Reinsurance related assets and liabilities	9,651,000	2,428,000
Other assets	6,254,000	(5,027,000)
Reserve for losses and loss adjustment expenses	8,420,000	3,561,000
Unearned premiums	27,743,000	24,576,000
Other liabilities	(3,592,000)	(7,393,000)
Net cash provided (used) by operating activities	73,354,000	69,372,000
Purchases of:
Fixed maturities, available for sale	(367,872,000)	(160,364,000)
Fixed maturities, trading	(4,162,000)	0
Equity investments	(67,129,000)	(35,400,000)
Other investments	(7,108,000)	(3,930,000)
Funding of qualified affordable housing project tax credit partnerships	0	(37,000)
Investment in unconsolidated subsidiaries	(21,985,000)	(5,613,000)
Proceeds from sales or maturities of:
Fixed maturities, available for sale	459,822,000	171,986,000
Equity investments	51,085,000	41,584,000
Other investments	6,092,000	6,788,000
Return of invested capital from unconsolidated subsidiaries	11,783,000	6,955,000
Net sales or maturities (purchases) of short-term investments	82,976,000	160,792,000
Unsettled security transactions, net change	22,421,000	6,296,000
Purchases of capital assets	(1,836,000)	(4,535,000)
Repayments (advances) under Syndicate Credit Agreement	(17,980,000)	1,159,000
Net cash provided (used) by investing activities	146,107,000	185,681,000
Financing Activities
Borrowings (repayments) under Revolving Credit Agreement	(40,000,000)	0
Repayments of Mortgage Loans	(349,000)	0
Dividends to shareholders	(266,734,000)	(265,664,000)
External capital contribution received for segregated portfolio cells	251,000	114,000
Other	(3,877,000)	(4,932,000)
Net cash provided (used) by financing activities	(310,709,000)	(270,482,000)
Increase (decrease) in cash and cash equivalents	(91,248,000)	(15,429,000)
Cash and cash equivalents at beginning of period	134,495,000	117,347,000
Cash and cash equivalents at end of period	43,247,000	101,918,000
Significant Non-Cash Transactions
Dividends declared and not yet paid	$ 16,616,000	$ 16,516,000

Basis of Presentation

Basis of Presentation	3 Months Ended
	Mar. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited Condensed Consolidated Financial Statements include the accounts of ProAssurance Corporation and its consolidated subsidiaries (ProAssurance, PRA or the Company). The financial statements have been prepared in accordance with GAAP for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and notes required by GAAP for complete financial statements. In the opinion of management, all adjustments considered necessary for a fair presentation, consisting of normal recurring adjustments, have been included. ProAssurance’s results for the three months ended March 31, 2018 are not necessarily indicative of the results that may be expected for the year ending December 31, 2018 . The accompanying Condensed Consolidated Financial Statements should be read in conjunction with the Consolidated Financial Statements and Notes contained in ProAssurance’s December 31, 2017 report on Form 10-K. In connection with its preparation of the Condensed Consolidated Financial Statements, ProAssurance evaluated events that occurred subsequent to March 31, 2018 for recognition or disclosure in its financial statements and notes to financial statements. ProAssurance operates in four reportable segments as follows: Specialty P&C , Workers' Compensation, Lloyd's Syndicate and Corporate. For more information on the nature of products and services provided and for financial information by segment, refer to Note 12 . Reclassifications In the second quarter of 2017, ProAssurance began presenting separately the components of underwriting, policy acquisition and operating expense as operating expense and DPAC amortization on the Condensed Consolidated Statements of Income and Comprehensive Income in order to provide additional details for investors. The Condensed Consolidated Statements of Income and Comprehensive Income for the three months ended March 31, 2017 have been reclassified to conform to the current period presentation. Total underwriting, policy acquisition and operating expense as well as net income for the three months ended March 31, 2017 was not affected by the change in presentation. Certain other insignificant prior period amounts have been reclassified to conform to the current period presentation. Other Liabilities Other liabilities consisted of the following: (In thousands) March 31, 2018 December 31, 2017 SPC dividends payable $ 47,122 $ 46,925 Unpaid dividends 16,616 267,292 All other 144,128 123,383 Total other liabilities $ 207,866 $ 437,600 SPC dividends payable are the cumulative undistributed earnings contractually payable to the external preferred shareholders of the SPC s operated by Eastern Re and Inova Re , ProAssurance's Cayman Islands reinsurance subsidiaries. Unpaid dividends represent common stock dividends declared by ProAssurance's Board that had not yet been paid as of March 31, 2018 . Unpaid dividends at December 31, 2017 reflected a special dividend declared in the fourth quarter of 2017 that was paid in January 2018 . Accounting Changes Adopted Restricted Cash ( ASU 2016-18) Effective for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years, the FASB issued guidance related to the classification of restricted cash presented in the statement of cash flows with the objective of reducing diversity in practice. Under the new guidance, entities are required to include restricted cash and restricted cash equivalents with cash and cash equivalents when reconciling beginning-of-period and end-of-period total amounts as presented on the statement of cash flows. ProAssurance adopted the guidance as of January 1, 2018. Adoption of the guidance had no material effect on ProAssurance’s results of operations, financial position or cash flows. Intra-Entity Transfers of Assets Other than Inventory ( ASU 2016-16) Effective for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years, the FASB issued guidance which reduces the complexity in accounting standards related to the income tax consequences of intra-entity transfers of assets other than inventory between tax-paying components. A tax-paying component is an individual entity or group of entities that is consolidated for tax purposes. Under the new guidance, entities are required to recognize income tax consequences of an intra-entity transfer of assets other than inventory when the transfer occurs instead of delaying recognition until the asset has been sold to an outside party. ProAssurance adopted the guidance as of January 1, 2018. Adoption of the guidance had no material effect on ProAssurance’s results of operations, financial position or cash flows. Classification of Certain Cash Receipts and Cash Payments ( ASU 2016-15) Effective for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years, the FASB issued guidance related to the classification of certain cash receipts and cash payments presented in the statement of cash flows with the objective of reducing diversity in practice. ProAssurance adopted the guidance as of January 1, 2018 and elected to use the cumulative earnings approach for presenting distributions from equity method investees. Adoption of the guidance had no material effect on ProAssurance’s results of operations or financial position; however, ProAssurance reclassified approximately $10.9 million in distributions from unconsolidated subsidiaries from investing activities to operating activities in the Condensed Consolidated Statement of Cash Flows for the three months ended March 31, 2017 . Revenue from Contracts with Customers ( ASU 2014-09) Effective for fiscal years beginning after December 15, 2017 the FASB issued guidance related to revenue from contracts with customers. The core principle of the new guidance is that revenue is recognized to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. ProAssurance adopted the guidance as of January 1, 2018 under the modified retrospective method. Adoption of the guidance had no material effect on ProAssurance’s results of operations, financial position or cash flows. Recognition and Measurement of Financial Assets and Financial Liabilities ( ASU 2016-01) Effective for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years, the FASB issued guidance that requires equity investments (except those accounted for under the equity method of accounting, or those that result in consolidation of the investee) to be measured at fair value with changes in fair value recognized in net income. The new guidance also specifies that an entity use the exit price notion when measuring the fair value of financial instruments for disclosure purposes and present financial assets and liabilities by measurement category and form of financial asset. Other provisions of the new guidance include: revised disclosure requirements related to the presentation in comprehensive income of changes in the fair value of liabilities; elimination, for public companies, of disclosure requirements relative to the methods and significant assumptions underlying fair values disclosed for financial instruments measured at amortized cost; and simplified impairment assessments for equity investments without readily determinable fair values. ProAssurance adopted the guidance as of January 1, 2018 using a modified retrospective application and recorded a cumulative-effect after-tax adjustment of approximately $8.3 million to beginning retained earnings in the Condensed Consolidated Statement of Changes in Capital for the three months ended March 31, 2018 . Adoption of the guidance had no material effect on ProAssurance’s results of operations, financial position or cash flows. Modification Accounting for Employee Share-Based Payment Awards ( ASU 2017-09) Effective for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years, the FASB issued guidance which reduces the complexity in accounting standards when there is a change in the terms or conditions of a share-based payment award. The new guidance clarifies that an entity should apply the modification accounting guidance if the value, vesting conditions or classification of the award changes. ProAssurance adopted the guidance as of January 1, 2018. Adoption of the guidance had no material effect on ProAssurance’s results of operations, financial position or cash flows. Reclassification of Certain Tax Effects from AOCI ( ASU 2018-02) Effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years, with early adoption permitted, the FASB issued guidance which permits a reclassification from AOCI to retained earnings for stranded tax effects resulting from the newly enacted federal corporate tax rate from the TCJA . The amount of the reclassification from AOCI to retained earnings will be the difference between the historical corporate tax rate and the newly enacted 21% corporate tax rate on deferred tax items originally established through OCI and not net income. The guidance allows entities to adopt in any interim or annual period for which financial statements have not yet been issued and apply the guidance either (1) in the period of adoption or (2) retrospectively to each period in which the effect of the change in the tax rate is recognized. ProAssurance adopted this guidance as of January 1, 2018 and elected to apply this guidance in the period of adoption using the specific identification method. Using a modified retrospective application, ProAssurance recorded a cumulative-effect adjustment which increased beginning AOCI by approximately $3.4 million and decreased beginning retained earnings by the same amount in the Condensed Consolidated Statement of Changes in Capital for the three months ended March 31, 2018 . Adoption of this guidance had no material effect on ProAssurance's financial position, results of operations or cash flows. Accounting Changes Not Yet Adopted Technical Corrections and Improvements to Financial Instruments - Overall ( ASU 2018-03) Effective for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years beginning after June 15, 2018, the FASB amended the new standard on recognizing and measuring financial assets and financial liabilities to clarify certain aspects of the guidance. Under the amended guidance, an entity that uses the measurement alternative for equity investments without readily determinable fair values can change its measurement approach to a fair value method through an irrevocable election that would apply to that security and all identical or similar investments of the same issuer. Also, entities are required to use the prospective transition approach only for equity investments they elect to measure using the new measurement alternative. Additionally, the guidance clarifies how to apply the measurement alternative and presentation requirements for financial liabilities measured under the fair value option. ProAssurance plans to adopt the guidance beginning July 1, 2018. As of March 31, 2018 , ProAssurance does not have any equity investments without readily determinable fair values or financial liabilities measured under the fair value option; therefore, adoption of the guidance is not expected to have a material effect on ProAssurance’s financial position, results of operations or cash flows. 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 and is currently in the process of evaluating all of its leases. As the majority of ProAssurance's leases are real estate operating leases and are not considered to be material, adoption of the guidance is not expected to have a material effect on ProAssurance’s results of operations, financial position or cash flows. 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 March 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. ProAssurance is in the process of evaluating the effect the new guidance would have on its results of operations and financial position and plans to adopt the guidance beginning January 1, 2020. 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.

Fair Value Measurement

Fair Value Measurement	3 Months Ended
	Mar. 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 March 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. March 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 $ — $ 129,751 $ — $ 129,751 U.S. Government-sponsored enterprise obligations — 29,959 — 29,959 State and municipal bonds — 329,995 — 329,995 Corporate debt, multiple observable inputs 2,334 1,230,832 — 1,233,166 Corporate debt, limited observable inputs — — 15,097 15,097 Residential mortgage-backed securities — 215,420 — 215,420 Agency commercial mortgage-backed securities — 14,887 — 14,887 Other commercial mortgage-backed securities — 29,195 — 29,195 Other asset-backed securities — 138,890 17,323 156,213 Fixed maturities, trading Corporate debt — 4,148 — 4,148 Equity investments Financial 74,556 — — 74,556 Utilities/Energy 46,637 — — 46,637 Consumer oriented 54,789 — — 54,789 Industrial 48,859 — — 48,859 Bond funds 153,256 — — 153,256 All other 93,847 — — 93,847 Short-term investments 288,019 61,100 — 349,119 Other investments 604 32,073 365 33,042 Other assets — 2,306 — 2,306 Total assets categorized within the fair value hierarchy $ 762,901 $ 2,218,556 $ 32,785 3,014,242 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 20,215 Investment in unconsolidated subsidiaries 277,094 Total assets at fair value $ 3,311,551 December 31, 2017 Fair Value Measurements Using Total (In thousands) Level 1 Level 2 Level 3 Fair Value Assets: Fixed maturities, available for sale U.S. Treasury obligations $ — $ 133,627 $ — $ 133,627 U.S. Government-sponsored enterprise obligations — 20,956 — 20,956 State and municipal bonds — 632,243 — 632,243 Corporate debt, multiple observable inputs 2,371 1,151,084 — 1,153,455 Corporate debt, limited observable inputs — — 13,703 13,703 Residential mortgage-backed securities — 196,789 1,055 197,844 Agency commercial mortgage-backed securities — 10,742 — 10,742 Other commercial mortgage-backed securities — 15,961 — 15,961 Other asset-backed securities — 97,780 3,931 101,711 Equity investments Financial 76,051 — — 76,051 Utilities/Energy 54,388 — — 54,388 Consumer oriented 54,529 — — 54,529 Industrial 53,936 — — 53,936 Bond funds 156,563 — — 156,563 All other 75,142 — — 75,142 Short-term investments 404,204 27,922 — 432,126 Other investments 607 31,155 409 32,171 Other assets — 1,731 — 1,731 Total assets categorized within the fair value hierarchy $ 877,791 $ 2,319,990 $ 19,098 3,216,879 Assets carried at NAV, which approximates fair value and which are not categorized within the fair value hierarchy, reported as a part of: Investment in unconsolidated subsidiaries 210,759 Other investments 20,130 Total assets at fair value $ 3,447,768 The fair values for securities included in the Level 2 category, with the few exceptions described below, were developed by one of several third party, nationally recognized pricing services, including services that price only certain types of securities. Each service uses complex methodologies to determine values for securities and subject the values they develop to quality control reviews. Management selected a primary source for each type of security in the portfolio and reviewed the values provided for reasonableness by comparing data to alternate pricing services and to available market and trade data. Values that appeared inconsistent were further reviewed for appropriateness. Any value that did not appear reasonable was discussed with the service that provided the value and adjusted, if necessary. There were no material changes to the values supplied by the pricing services during the three months ended March 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. Short-term investments were securities maturing within one year, carried at cost which approximated the fair value of the security due to the short term to maturity. 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 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 processes and methodologies used as well as quantitative information regarding securities in the Level 3 category. Level 3 Valuation Processes • Level 3 securities are priced by the Chief Investment Officer. • Level 3 valuations are computed quarterly. Prices are evaluated quarterly against prior period prices and the expected change in prices. • ProAssurance's Level 3 securities are primarily NRSRO rated debt instruments for which comparable market inputs are commonly available for evaluating the securities in question. Valuation of these debt instruments is not overly sensitive to changes in the unobservable inputs used. 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 March 31, 2018 , 87% 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 March 31, 2018 , 78% 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 March 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) March 31, 2018 December 31, 2017 Valuation Technique Unobservable Input Range Assets: Corporate debt, limited observable inputs $15,097 $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 $17,323 $4,986 Market Comparable Comparability Adjustment 0% - 5% (2.5%) Discounted Cash Flows Comparability Adjustment 0% - 5% (2.5%) Other investments $365 $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. March 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 (38 ) — — (38 ) Net realized investment gains (losses) — — (44 ) (44 ) Included in other comprehensive income (38 ) (30 ) — (68 ) Purchases 6,005 13,453 — 19,458 Sales (2,905 ) (27 ) — (2,932 ) Transfers in 2,069 — — 2,069 Transfers out (3,699 ) (1,059 ) — (4,758 ) Balance March 31, 2018 $ 15,097 $ 17,323 $ 365 $ 32,785 Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end $ — $ — $ — $ — March 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 (39 ) — — (39 ) Net realized investment gains (losses) 13 — — 13 Included in other comprehensive income (208 ) (5 ) 2 (211 ) Purchases 7,048 — — 7,048 Sales (1,712 ) — — (1,712 ) Transfers in — — 898 898 Transfers out (998 ) — — (998 ) Balance March 31, 2017 $ 18,914 $ 3,002 $ 903 $ 22,819 Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end $ — $ — $ — $ — Transfers There were no transfers between the Level 1 and Level 2 categories during the three months ended March 31, 2018 . During the three months ended March 31, 2017 , equity securities of approximately $35.4 million were transferred from Level 2 to Level 1. Transfers shown in the preceding Level 3 tables were as of the end of the quarter in which the transfer occurred. All transfers were to or from Level 2. All transfers during the three months ended March 31, 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 March 31, 2018 and December 31, 2017 , certain LP s/ LLC s and investment funds measure fund assets at fair value on a recurring basis and provide a NAV for ProAssurance's interest. The carrying value of these interests is based on the NAV provided and was considered to approximate the fair value of the interests. For investment in unconsolidated subsidiaries, ProAssurance recognizes any changes in the NAV of its interests in equity in earnings (loss) of unconsolidated subsidiaries during the period of change. In accordance with GAAP , the fair value of these investments was not classified within the fair value hierarchy. The amount of ProAssurance's unfunded commitments related to these investments as of March 31, 2018 and fair values of these investments as of March 31, 2018 and December 31, 2017 was as follows: Unfunded Fair Value (In thousands) March 31, March 31, December 31, Equity investments: Mortgage fund (1)* None $ 20,215 $ — Investment in unconsolidated subsidiaries: Private debt funds (2) $4,976 32,064 42,206 Long equity fund (3) None 7,957 7,847 Long/short equity funds (4) None 32,177 31,352 Non-public equity funds (5) $82,135 105,049 100,062 Multi-strategy fund of funds (6) None 9,274 9,100 Credit funds (7) None 17,789 6,561 Long/short commodities fund (8) None 13,063 13,025 Strategy focused funds (9) $19,241 59,721 606 277,094 210,759 Other investments: Mortgage fund (1)* See above — 20,130 Total investments carried at NAV $ 297,309 $ 230,889 * In the first quarter of 2018, ProAssurance began presenting this investment previously reported as a part of other investments as a part of equity investments on the Condensed Consolidated Balance Sheet as of March 31, 2018. Prior year amounts have not been reclassified. Below is additional information regarding each of the investments listed in the table above as of March 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) The investment is comprised of interests in two 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 does not permit redemption. Income and capital are to be periodically distributed at the discretion of the LP s over an anticipated time frame that spans from three to eight years. (3) The fund is a LP that holds long equities of public international companies. Redemptions are allowed at the end of any calendar month with a prior notice requirement of 15 days and are paid within 10 days of the end of the calendar month of the redemption request. (4) The investment is comprised of interests in multiple unrelated LP funds. The funds hold primarily long and short North American equities and target absolute returns using strategies designed to take advantage of market opportunities. The funds generally permit quarterly or semi-annual capital redemptions subject to notice requirements of 30 to 90 days . For some funds, redemptions above specified thresholds (lowest threshold is 90% ) may be only partially payable until after a fund audit is completed and are then payable within 30 days . (5) The investment is comprised of interests in multiple unrelated LP funds, each structured to provide capital appreciation through diversified investments in private equity, which can include investments in buyout, venture capital, debt including senior, second lien and mezzanine, distressed debt and other private equity-oriented LP s. Two of the LP s allow redemption by terms set forth in the LP agreements; the others do not permit redemption. Income and capital are to be periodically distributed at the discretion of the LP over time frames that are anticipated to span up to nine years. (6) This fund is a LLC structured to build and manage low volatility, multi-manager portfolios that have little or no correlation to the broader fixed income and equity security markets. Redemptions are not permitted but offers to repurchase units of the LLC may be extended periodically. (7) The investment is comprised of two unrelated LP funds. One fund seeks to obtain superior risk-adjusted absolute returns through a diversified portfolio of debt securities, including bonds, loans and other asset-backed instruments. The second fund seeks event driven opportunities across the corporate credit spectrum. For both funds, redemptions are allowed at any quarter-end with a prior notice requirement of 90 days . (8) This fund is a LLC invested across a broad range of commodities and focuses primarily on market neutral, relative value strategies, seeking to generate absolute returns with low correlation to broad commodity, equity and fixed income markets. Following an initial one-year lock-up period, redemptions are allowed with a prior notice requirement of 30 days and are payable within 30 days . (9) The investment is comprised of multiple unrelated LP funds. One fund is a LLC focused on investing in North American consumer products companies, comprised of equity and equity-related securities, as well as debt instruments. Redemptions are not permitted. Another fund is a LP focused on North American energy infrastructure assets that allows redemption with consent of the General Partner. The remaining funds are real estate focused LP s, one of which allows for redemption with prior notice. ProAssurance may not sell, transfer or assign its interest in any of the above LP s/ LLC s without special consent from the LP s/ LLC s. Nonrecurring Fair Value Measurement At March 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 our financial instruments that, in accordance with GAAP for the type of investment, are measured using a methodology other than fair value. All fair values provided primarily fall within the Level 3 fair value category. March 31, 2018 December 31, 2017 (In thousands) Carrying Fair Carrying Fair Financial assets: BOLI $ 62,562 $ 62,562 $ 62,113 $ 62,113 Other investments $ 2,902 $ 2,902 $ 58,546 $ 69,095 Other assets $ 49,549 $ 48,816 $ 34,020 $ 33,742 Financial liabilities: Senior notes due 2023* $ 250,000 $ 269,418 $ 250,000 $ 273,153 Revolving Credit Agreement* $ 83,000 $ 83,000 $ 123,000 $ 123,000 Mortgage loans* $ 40,111 $ 40,111 $ 40,460 $ 40,460 Other liabilities $ 21,525 $ 21,525 $ 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 $21.6 million and $20.2 million at March 31, 2018 and December 31, 2017 , respectively. The deferred compensation liabilities are adjusted to match the fair value of the deferred compensation assets. Other assets also included a secured note receivable and unsecured note receivable under two separate line of credit agreements. Fair value of these notes receivable was based on the present value of expected cash flows from the notes receivable, discounted at market rates on the valuation date for receivables with similar credit standings and similar payment structures. The fair value of the debt was estimated based on the present value of expected future cash outflows, discounted at rates available on the valuation date for similar debt issued by entities with a similar credit standing to ProAssurance.

Investments

Investments	3 Months Ended
	Mar. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Investments	Investments Available-for-sale fixed maturities at March 31, 2018 and December 31, 2017 included the following: March 31, 2018 (In thousands) Amortized Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Fixed maturities, available for sale U.S. Treasury obligations $ 131,655 $ 305 $ 2,209 $ 129,751 U.S. Government-sponsored enterprise obligations 30,377 27 445 29,959 State and municipal bonds 324,336 6,613 954 329,995 Corporate debt 1,259,132 7,008 17,877 1,248,263 Residential mortgage-backed securities 217,891 1,502 3,973 215,420 Agency commercial mortgage-backed securities 15,078 29 220 14,887 Other commercial mortgage-backed securities 29,409 100 314 29,195 Other asset-backed securities 157,506 40 1,333 156,213 $ 2,165,384 $ 15,624 $ 27,325 $ 2,153,683 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 March 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 $ 131,655 $ 31,700 $ 73,858 $ 21,321 $ 2,872 $ 129,751 U.S. Government-sponsored enterprise obligations 30,377 — 8,009 21,814 136 29,959 State and municipal bonds 324,336 29,481 111,512 140,004 48,998 329,995 Corporate debt 1,259,132 115,385 682,646 404,159 46,073 1,248,263 Residential mortgage-backed securities 217,891 215,420 Agency commercial mortgage-backed securities 15,078 14,887 Other commercial mortgage-backed securities 29,409 29,195 Other asset-backed securities 157,506 156,213 $ 2,165,384 $ 2,153,683 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 March 31, 2018 . Cash and securities with a carrying value of $45.8 million at March 31, 2018 were on deposit with various state insurance departments to meet regulatory requirements. ProAssurance also held securities with a carrying value of $120.1 million at March 31, 2018 that are pledged as collateral security for advances under the Revolving Credit Agreement (see Note 7 for additional detail on the Revolving Credit Agreement ). As a member of Lloyd's and a capital provider to Syndicate 1729 and Syndicate 6131 , which began active operations on January 1, 2018, ProAssurance is required to maintain capital at Lloyd's , referred to as FAL . ProAssurance's FAL investments at March 31, 2018 included fixed maturities with a fair value of $123.5 million and short-term investments with a fair value of approximately $0.4 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 March 31, 2018 and December 31, 2017 , including the length of time the investment had been held in a continuous unrealized loss position. March 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 $ 121,718 $ 2,209 $ 87,740 $ 1,438 $ 33,978 $ 771 U.S. Government-sponsored enterprise obligations 29,018 445 22,252 218 6,766 227 State and municipal bonds 63,690 954 55,761 620 7,929 334 Corporate debt 848,499 17,877 733,344 13,216 115,155 4,661 Residential mortgage-backed securities 175,295 3,973 132,075 2,066 43,220 1,907 Agency commercial mortgage-backed securities 9,547 220 7,638 101 1,909 119 Other commercial mortgage-backed securities 19,145 314 15,723 256 3,422 58 Other asset-backed securities 118,780 1,333 105,370 1,134 13,410 199 $ 1,385,692 $ 27,325 $ 1,159,903 $ 19,049 $ 225,789 $ 8,276 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 March 31, 2018 , excluding U.S. Government or U.S. Government-sponsored enterprise obligations, there were 943 debt securities ( 44.9% of all available-for-sale fixed maturity securities held) in an unrealized loss position representing 494 issuers. The greatest and second greatest unrealized loss positions among those securities were approximately $0.5 million and $0.4 million , respectively. The securities were evaluated for OTTI as of March 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 of the Notes to Consolidated Financial Statements included in ProAssurance's December 31, 2017 Form 10-K. Fixed maturity securities held in an unrealized loss position at March 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 March 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: Three Months Ended March 31 (In millions) 2018 2017 Proceeds from sales (exclusive of maturities and paydowns) $ 379.2 $ 79.2 Purchases $ 367.9 $ 160.4 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 Condensed Consolidated Balance Sheet as of March 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 cost, which approximates fair value. BOLI ProAssurance holds BOLI policies that are carried at the current cash surrender value of the policies (original cost $33 million ). All insured individuals were members of ProAssurance management at the time the policies were acquired. The primary purpose of the program is to offset future employee benefit expenses through earnings on the cash value of the policies. ProAssurance is the owner and beneficiary of these policies. Net Investment Income Net investment income by investment category was as follows: Three Months Ended (In thousands) 2018 2017 Fixed maturities $ 17,080 $ 20,121 Equities 4,867 3,644 Short-term investments, including Other 1,308 801 BOLI 449 455 Investment fees and expenses (1,677 ) (1,835 ) Net investment income $ 22,027 $ 23,186 Investment in Unconsolidated Subsidiaries ProAssurance's investment in unconsolidated subsidiaries were as follows: March 31, 2018 Carrying Value (In thousands) Percentage March 31, December 31, Qualified affordable housing project tax credit partnerships See below $ 80,507 $ 84,607 Other tax credit partnerships See below 5,735 6,118 All other investments, primarily investment fund LPs/LLCs See below 314,788 239,866 $ 401,030 $ 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 $30.7 million at March 31, 2018 and $32.5 million at December 31, 2017 . ProAssurance's ownership percentage relative to the remaining tax credit partnership interests is less than 20% ; these interests had a carrying value of $49.8 million at March 31, 2018 and $52.1 million at December 31, 2017 . Since ProAssurance has the ability to exert influence over the partnerships but does not control them, all are accounted for using the equity method. See further discussion of the entities in which ProAssurance holds passive interests in Note 10 . Other tax credit partnerships are comprised entirely of historic tax credits. The historic tax credits 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 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 10 . 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 three 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 $31.3 million at March 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 $283.5 million at March 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 investments and historic tax credit investments. The losses recorded reflect ProAssurance's allocable portion of partnership operating losses. Losses from qualified affordable housing project tax credit investments were $4.1 million and $3.3 million for the 2018 and 2017 three-month period s, respectively, and tax credits recognized related to these investments totaled $4.6 million for both the 2018 and 2017 three-month period s. Losses from historic tax credit investments were $1.9 million and $0.4 million and tax credits recognized related to these investments totaled $0.7 million and $1.8 million for the 2018 and 2017 three-month period s, respectively. Tax credits recognized reduced income tax expense in the respective periods. Net Realized Investment Gains (Losses) Realized investment gains and losses are recognized on the first-in, first-out basis. The following table provides detailed information regarding net realized investment gains (losses): Three Months Ended (In thousands) 2018 2017 Total OTTI losses: Corporate debt $ — $ (419 ) Portion of OTTI losses recognized in other comprehensive income before taxes: Corporate debt — 248 Net impairment losses recognized in earnings — (171 ) Gross realized gains, available-for-sale fixed maturities 4,464 1,853 Gross realized (losses), available-for-sale fixed maturities (2,047 ) (67 ) Net realized gains (losses), equity investments 9,219 6,562 Net realized gains (losses), other investments 688 1,172 Change in unrealized holding gains (losses), trading fixed maturities (49 ) — Change in unrealized holding gains (losses), equity investments (23,845 ) 3,616 Change in unrealized holding gains (losses), convertible securities, carried at fair value (954 ) 313 Other 7 2 Net realized investment gains (losses) $ (12,517 ) $ 13,280 ProAssurance did no t recognize any OTTI during the first quarter of 2018 . During the first quarter of 2017, ProAssurance recognized OTTI in earnings of $0.2 million and $0.2 million of non-credit OTTI in OCI, both of which related to corporate bonds. The following table presents a roll forward of cumulative credit losses recorded in earnings related to impaired debt securities for which a portion of the OTTI was recorded in OCI . Three Months Ended March 31 (In thousands) 2018 2017 Balance beginning of period $ 1,313 $ 1,158 Additional credit losses recognized during the period, related to securities for which: No OTTI has been previously recognized — 171 Balance March 31 $ 1,313 $ 1,329

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes ProAssurance estimates its annual effective tax rate at the end of each quarterly reporting period and uses this estimated rate to record the provision for income taxes in the interim financial statements. The provision for income taxes is different from that which would be obtained by applying the statutory federal income tax rate to income before income taxes primarily because a portion of ProAssurance’s investment income is tax-exempt, and because ProAssurance utilizes tax credit benefits transferred from tax credit partnership investments. In addition, ProAssurance's provision for income taxes in 2018 was impacted by certain provisions of the TCJA , as discussed below. ProAssurance had a total liability for federal and U.K. income taxes of $6.3 million at March 31, 2018 and $8.0 million at December 31, 2017 , both carried as a part of other liabilities. The liability for unrecognized tax benefits, which is included in the total liability for federal and U.K. income taxes, was $5.2 million and $5.8 million at March 31, 2018 and December 31, 2017 , respectively, which included an accrued liability for interest of approximately $0.6 million and $0.5 million , respectively. Tax Cuts and Jobs Act The TCJA was signed into law on December 22, 2017 and contains several key provisions that impact the Company's business, including the reduction of the U.S. federal corporate tax rate from 35% to 21% effective January 1, 2018, the reduction in the amount of executive compensation that could qualify as a tax deduction, a minimum tax on payments made to related foreign entities and a change in how property and casualty taxpayers discount loss reserves. Effective January 1, 2018, the TCJA introduced a minimum tax on payments made to related foreign entities referred to as the BEAT . The BEAT is imposed by adding back into the U.S. tax base any base erosion payment made by the U.S. taxpayer to a related foreign entity and applying a minimum tax rate to this newly calculated modified taxable income. Base erosion payments represent any amount paid or accrued by the U.S. taxpayer to a related foreign entity for which a deduction is allowed. Premiums the Company cedes to the SPC s at its newly formed wholly owned Cayman Islands reinsurance subsidiary, Inova Re , do not fall within the scope of base erosion payments as the SPC s at Inova Re intend to elect to be taxed as U.S. taxpayers. However, premiums the Company cedes to the one 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 12 . Management has evaluated its exposure to the BEAT and has concluded that the Company’s outbound deductible payments to related foreign entities are below the threshold for application of the BEAT ; therefore, ProAssurance has not recognized any incremental tax expense for the BEAT provision of the TCJA for the three months ended March 31, 2018 . ProAssurance was able to complete its accounting for all areas of the TCJA during the period of enactment except as described below. Provisional amount As noted in ProAssurance's December 31, 2017 Form 10-K, ProAssurance was able to make a reasonable estimate of the effects on its existing deferred tax asset balances at December 31, 2017 as it relates to the limitation on the future deductibility of certain executive compensation and recorded a provisional charge to income tax expense from continuing operations for the year ended December 31, 2017 . As of March 31, 2018 , ProAssurance has not made any measurement-period adjustments to this provisional amount and any future guidance from the IRS addressing the effects of the TCJA on executive compensation could result in a material change to this provisional amount. Provisional amount not reasonably estimable As noted in ProAssurance's December 31, 2017 Form 10-K, ProAssurance was unable to reasonably estimate the impact of the change in loss reserve discounting factors due to the TCJA ; therefore, no provisional amount was recorded at December 31, 2017 . As of March 31, 2018 , the IRS has yet to release the 2018 discount factors; therefore, ProAssurance has not adjusted its deferred tax balances due to the enactment of the TCJA . ProAssurance continues to utilize the discount factors based on existing accounting guidance and the provisions of the tax laws that were in effect immediately prior to enactment of the TCJA . Once the IRS releases the 2018 loss reserve discount factors, ProAssurance will complete its analysis and include the effect of the difference in the reserve discount factors in the period the analysis is complete or the impact is reasonably estimable.

Reserve for Losses and Loss Adj

Reserve for Losses and Loss Adjustment Expenses	3 Months Ended
	Mar. 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. Claims may be resolved over an extended period of time, often five years or more, and may be subject to litigation. Estimating losses requires ProAssurance to make and revise judgments and assessments regarding multiple uncertainties over an extended period of time. As a result, the reserve estimate may vary considerably from the eventual outcome. The assumptions used in establishing ProAssurance’s reserve are regularly reviewed and updated by management as new data becomes available. Changes to estimates of previously established reserves are included in earnings in the period in which the estimate is changed. ProAssurance believes that the methods it uses to establish reserves are reasonable and appropriate. Each year, ProAssurance uses internal actuaries to review the reserve for losses of each insurance subsidiary. ProAssurance also engages consulting actuaries to review ProAssurance claims data and provide observations regarding cost trends, rate adequacy and ultimate loss costs. ProAssurance considers the views of the actuaries as well as other factors, such as known, anticipated or estimated changes in frequency and severity of claims, loss retention levels and premium rates, in establishing the amount of its reserve for losses. The statutory filings of each insurance company with the insurance regulators must be accompanied by a consulting actuary's certification as to their respective reserves. ProAssurance partitions its reserve by accident year, which is the year in which the claim becomes its liability. As claims are incurred (reported) and claim payments are made, they are aggregated by accident year for analysis purposes. ProAssurance also partitions its reserve by reserve type: case reserves and IBNR reserves. Case reserves are established by the claims department based upon the particular circumstances of each reported claim and represent ProAssurance’s estimate of the future loss costs (often referred to as expected losses) that will be paid on reported claims. Case reserves are decremented as claim payments are made and are periodically adjusted upward or downward as estimates regarding the amount of future losses are revised; a reported loss for an individual claim equates to the case reserve at any point in time plus the claim payments that have been made to date. IBNR reserves represent an estimate, in the aggregate, of future development on losses that have been reported to ProAssurance plus an estimate of losses that have been incurred but not reported. Development of Prior Accident Years In addition to setting the initial reserve for the current accident year, each period ProAssurance reassesses the amount of reserve required for prior accident years. The foundation of ProAssurance’s reserve re-estimation process is an actuarial analysis that is performed by both the internal and consulting actuaries. This detailed analysis projects ultimate losses based on partitions which include line of business, geography, coverage layer and accident year. The procedure uses the most representative data for each partition, capturing its unique patterns of development and trends. In all, there are 200 different partitions of ProAssurance's business for purposes of this analysis. ProAssurance believes that the use of consulting actuaries provides an independent view of the loss data as well as a broader perspective on industry loss trends. Activity in the reserve for losses and loss adjustment expenses is summarized as follows: (In thousands) Three Months Ended March 31, 2018 Three Months Ended March 31, 2017 Year Ended December 31, 2017 Balance, beginning of year $ 2,048,381 $ 1,993,428 $ 1,993,428 Less reinsurance recoverables on unpaid losses and loss adjustment expenses 335,585 273,475 273,475 Net balance, beginning of year 1,712,796 1,719,953 1,719,953 Net losses: Current year 152,572 147,927 603,518 Favorable development of reserves established in prior years, net (22,786 ) (28,776 ) (134,360 ) Total 129,786 119,151 469,158 Paid related to: Current year (14,243 ) (33,085 ) (106,633 ) Prior years (101,078 ) (80,709 ) (369,682 ) Total paid (115,321 ) (113,794 ) (476,315 ) Net balance, end of period 1,727,261 1,725,310 1,712,796 Plus reinsurance recoverables on unpaid losses and loss adjustment expenses 329,540 271,679 335,585 Balance, end of period $ 2,056,801 $ 1,996,989 $ 2,048,381 The favorable loss development of $22.8 million recognized in the three months ended March 31, 2018 primarily reflected a lower than anticipated claims severity trend (i.e., the average size of a claim) for accident years 2011 through 2015 . The favorable loss development of $28.8 million recognized in the three months ended March 31, 2017 primarily reflected a lower than anticipated claims severity trend for accident years 2009 through 2014 . The favorable loss development of $134.4 million recognized in the twelve months ended December 31, 2017 primarily reflected a lower than anticipated claims severity trend for accident years 2010 through 2014. For additional information regarding ProAssurance's reserve for losses, see Note 1 and Note 7 of the Notes to Consolidated Financial Statements included in ProAssurance's December 31, 2017 Form 10-K.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 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 in Note 1 of the Notes to Consolidated Financial Statements in ProAssurance's 2017 Form 10-K. As a member of Lloyd's , ProAssurance is required to provide capital to support its Lloyd's Syndicates through 2022 of up to $200 million , referred to as FAL . At March 31, 2018 , ProAssurance is satisfying the FAL requirement with investment securities on deposit with Lloyd's with a carrying value of $123.9 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 March 31, 2018 , the unused commitment under the Syndicate Credit Agreement approximated £3.3 million (approximately $4.6 million ).

Debt

Debt	3 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
Debt	Debt ProAssurance’s outstanding debt consisted of the following: (In thousands) March 31, December 31, Senior Notes due 2023, unsecured, interest at 5.3% annually $ 250,000 $ 250,000 Revolving Credit Agreement, outstanding borrowings are fully secured, see Note 3, and carried at a weighted average interest rate of 2.24% and 1.91%, respectively. Outstanding borrowings are not permitted to exceed $250 million aggregately; Revolving Credit Agreement expires in 2020. The interest rate on the borrowings is set at the time the respective borrowing is initiated or renewed. The current borrowing can be repaid or renewed in the second quarter of 2018. If renewed, the interest rate will be reset. 83,000 123,000 Mortgage Loans, outstanding borrowings are secured by first priority liens on two office buildings, and bear an interest rate of three-month LIBOR plus 1.325% (3.42% and 2.86%, respectively) determined on a quarterly basis. 40,111 40,460 Total principal 373,111 413,460 Less debt issuance costs 1,583 1,649 Debt less debt issuance costs $ 371,528 $ 411,811 Covenant Compliance There are no financial covenants associated with the Senior Notes due 2023. The Revolving Credit Agreement contains customary representations, covenants and events constituting default, and remedies for default. The Revolving Credit Agreement also defines financial covenants regarding permitted leverage ratios. ProAssurance is currently in compliance with all covenants of the Revolving Credit Agreement . The Mortgage Loans contain customary representations, covenants and events constituting default, and remedies for default. The Mortgage Loans also define a financial covenant regarding a permitted leverage ratio for each of the two ProAssurance subsidiaries that entered into the Mortgage Loans. ProAssurance's subsidiaries are currently in compliance with the financial covenant of the Mortgage Loans. Additional Information For additional information regarding ProAssurance's debt, see Note 9 of the Notes to Consolidated Financial Statements included in ProAssurance's December 31, 2017 Form 10-K.

Derivatives

Derivatives	3 Months Ended
	Mar. 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 March 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 7 . Under the terms of the interest rate cap agreement, ProAssurance paid a premium of $2 million in the fourth quarter of 2017 for the right to receive cash payments based upon a notional amount of $35 million if and when the three-month LIBOR rises above 235 basis points. The Company's variable-rate Mortgage Loans bear an interest rate of three-month LIBOR plus 132.5 basis points. Therefore, this derivative instrument is effectively ensuring the interest rate related to the Mortgage Loans is capped at a maximum of 367.5 basis points until expiration of the interest rate cap agreement in October 2027 . ProAssurance has designated the interest rate cap as an economic hedge (non-hedging instrument) of interest rate exposure and any change in fair value of the derivative is immediately recognized in earnings during the period of change. The following table provides a summary of the volume and fair value position of the interest rate cap as well as the reporting location in the Condensed Consolidated Balance Sheets as of March 31, 2018 and December 31, 2017 . ($ in thousands) March 31, 2018 December 31, 2017 Derivatives Not Designated as Hedging Instruments Location in the Condensed Consolidated Balance Sheets Number of Instruments Notional Amount (1) Estimated Fair Value (2) Number of Instruments Notional Amount (1) Estimated Fair Value (2) Interest Rate Cap Other assets 1 $ 35,000 $ 2,306 1 $ 35,000 $ 1,731 (1) Volume is represented by the derivative instrument's notional amount. (2) Additional information regarding the fair value of the Company's interest rate cap is provided in Note 2. The following table presents the pre-tax impact of the change in the fair value of the interest rate cap and the reporting location in the Condensed Consolidated Statements of Income and Comprehensive Income for the three months ended March 31, 2018 and 2017 . Gains (Losses) Recognized in Income on Derivatives (In thousands) Three Months Ended March 31 Derivatives Not Designated as Hedging Instruments Location in the Condensed Consolidated Statements of Income and Comprehensive Income 2018 2017 Interest Rate Cap Interest expense $ 575 $ — As a result of this derivative instrument, ProAssurance is exposed to risk that the counterparty will fail to meet their 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 March 31, 2018 , the counterparty had an investment grade rating of BBB- and has performed in accordance with their contractual obligations.

Shareholders' Equity

Shareholders' Equity	3 Months Ended
	Mar. 31, 2018
Equity [Abstract]
Shareholders' Equity	Shareholders’ Equity At March 31, 2018 and December 31, 2017 , ProAssurance had 100 million shares of authorized common stock and 50 million shares of authorized preferred stock. The Board has the authority to determine provisions for the issuance of preferred shares, including the number of shares to be issued, the designations, powers, preferences and rights, and the qualifications, limitations or restrictions of such shares. To date, the Board has not approved the issuance of preferred stock. ProAssurance declared cash dividends of $0.31 per share during the first quarters of both 2018 and 2017 , totaling $16.6 million and $16.5 million , respectively. At March 31, 2018 , Board authorizations for the repurchase of common shares or the retirement of outstanding debt of $109.6 million remained available for use. ProAssurance did no t repurchase any common shares during the three months ended March 31, 2018 and 2017. Share-based compensation expense and related tax benefits were as follows: Three Months Ended March 31 (In thousands) 2018 2017 Share-based compensation expense $ 902 $ 3,346 Related tax benefits $ 190 $ 1,171 ProAssurance awarded approximately 85,800 restricted share units and 27,200 base performance share units to employees in February 2018 . The fair value of each unit awarded was estimated at $44.73 , equal to the market value of a ProAssurance common share on the date of grant less the estimated present value of dividends during the vesting period. All awards are charged to expense as an increase to additional paid-in capital over the service period (generally the vesting period) associated with the award. Restricted share units and performance share units vest in their entirety at the end of a three -year period following the grant date based on a continuous service requirement and, for performance share units, achievement of a performance objective. Partial vesting is permitted for retirees. A ProAssurance common share is issued for each unit once vesting requirements are met, except that units sufficient to satisfy required tax withholdings are paid in cash. The number of common shares issued for performance share units varies from 50% to 200% of base awards depending upon the degree to which stated performance objectives are achieved. ProAssurance issued approximately 52,800 and 80,600 common shares to employees in February 2018 related to restricted share units and performance share units, respectively, granted in 2015. Performance share units for the 2015 award were issued at a level of 125% . ProAssurance issued approximately 2,500 common shares to employees in February 2018 as bonus compensation, as approved by the Compensation Committee of the Board. The shares issued were valued at fair value (the market price of a ProAssurance common share on the date of award). Other Comprehensive Income (Loss) and Accumulated Other Comprehensive Income (Loss) For the three months ended March 31, 2018 and 2017 , OCI was almost entirely comprised of unrealized gains and losses, including non-credit impairment losses, arising during the period related to fixed maturity available-for-sale securities, less reclassification adjustments, as shown in the table that follows, net of tax. For the three months ended March 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. At March 31, 2018 and December 31, 2017 , AOCI was almost entirely comprised of accumulated unrealized gains and losses from fixed maturity available-for-sale securities, including accumulated non-credit impairments recognized through OCI of $0.6 million and $0.5 million , respectively, net of tax. At March 31, 2018 and December 31, 2017 , accumulated changes in the defined benefit plan liability not yet recognized in earnings were nominal in amount. Due to the adoption of accounting guidance in the first quarter of 2018 related to certain impacts of the TCJA, ProAssurance increased AOCI by approximately $3.4 million with a corresponding decrease to retained earnings of the same amount as of the beginning of 2018. See Note 1 for additional information on accounting guidance adopted during the period. At March 31, 2018 and December 31, 2017, tax effects were computed using the enacted federal corporate tax rate of 21% and 35% , respectively, with the exception of unrealized gains and losses on available-for-sale securities held at our U.K. and Cayman Islands entities which in both periods were immaterial in amount. Amounts reclassified from AOCI to net income and the amounts of deferred tax expense (benefit) included in OCI were as follows: Three Months Ended March 31 (In thousands) 2018 2017 Reclassifications from AOCI to net income: Realized investment gains (losses) $ 2,417 $ 1,616 Tax effect* (508 ) (566 ) Net reclassification adjustments $ 1,909 $ 1,050 Deferred tax expense (benefit) included in OCI $ (7,060 ) $ 1,481 * Tax effects were computed using a 21% and 35% rate for the three months ended March 31, 2018 and 2017, respectively.

Variable Interest Entities

Variable Interest Entities	3 Months Ended
	Mar. 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. At March 31, 2018 , ProAssurance's VIE interests totaled $316.3 million carried as a part of investment in unconsolidated subsidiaries. ProAssurance does not have power over the activities that most significantly impact the economic performance of these VIE s and thus is not the primary beneficiary. Therefore, ProAssurance has not consolidated these VIE s. ProAssurance’s involvement with each VIE is limited to its direct ownership interest in the VIE . Except for the funding commitments disclosed in Note 6 , ProAssurance has no arrangements with any of the VIE s to provide other financial support to or on behalf of the VIE . At March 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	3 Months Ended
	Mar. 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) Three Months Ended March 31 2018 2017 Weighted average number of common shares outstanding, basic 53,515 53,315 Dilutive effect of securities: Restricted Share Units 82 78 Performance Share Units 66 121 Purchase Match Units 19 21 Weighted average number of common shares outstanding, diluted 53,682 53,535 Effect of dilutive shares on earnings per share $ — $ (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. There were no common share equivalents that were antidilutive for the three months ended March 31, 2018 or 2017 .

Segment Information

Segment Information	3 Months Ended
	Mar. 31, 2018
Segment Reporting [Abstract]
Segment Information	Segment Information ProAssurance operates in four segments that are organized around the nature of the products and services provided: Specialty P&C , Workers' Compensation, Lloyd's Syndicate and Corporate. A description of each segment 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 Syndicate 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 Syndicate segment results are typically reported on a quarter delay. For consistency purposes, results from this ceding arrangement, other than cash receipts or disbursements, have been reported within the Specialty P&C segment on the same one-quarter delay. Workers' Compensation provides workers' compensation products primarily to employers with 1,000 or fewer employees. The segment also offers alternative market solutions whereby policies written are 100% ceded either to captive insurers unaffiliated with ProAssurance or to SPC s operated by wholly owned subsidiaries of ProAssurance. Each SPC is owned, fully or in part, by an agency, group or association. Operating results (underwriting profit or loss, plus investment results reported in the Corporate segment) of the SPC s are due to the owners of that cell. During the first quarter of 2018, ProAssurance reorganized its Cayman Islands SPC operations. Beginning in 2018, all new and renewing alternative market business previously ceded to the SPCs at Eastern Re , with the exception of one program, is now ceded to SPC s operated by a newly formed wholly owned Cayman Islands subsidiary, Inova Re . As part of the reorganization, all SPC s previously operated by Eastern Re , with the exception of one program, ceased assuming new and renewing business on or after January 1, 2018. The external cell owners' cumulative undistributed earnings and the results of all SPCs for the current period due to external cell owners continue to be reported as SPC dividends payable and SPC dividend expense, respectively. Lloyd's Syndicate includes operating results from ProAssurance's 58% participation in Lloyd's of London Syndicate 1729 . Syndicate 1729 underwrites risks over a wide range of property and casualty insurance and reinsurance lines in both the U.S. and international markets. The results of this segment are 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 effective January 1, 2018; however, due to the quarter delay these changes will not be reflected in the Lloyd's Syndicate segment results until the second quarter of 2018. Syndicate 6131 , a newly formed SPA, focuses on contingency and specialty property business. Corporate includes ProAssurance's investment operations, interest expense and U.S. income taxes, all of which are managed at the corporate level with the exception of investment assets solely allocated to Lloyd's Syndicate operations as discussed above. The segment also includes non-premium revenues generated outside of the Company's insurance entities and corporate expenses. The accounting policies of the segments are the same as those described in Note 1 of the Notes to Consolidated Financial Statements in ProAssurance’s December 31, 2017 report on Form 10-K and Note 1 of the Notes to Condensed Consolidated Financial Statements. ProAssurance evaluates performance of its Specialty P&C and Workers' Compensation segments based on before tax underwriting profit or loss, which excludes investment performance. Performance of the Lloyd's Syndicate 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 and other assets are not managed at the segment level. Financial results by segment were as follows: Three Months Ended March 31, 2018 (In thousands) Specialty P&C Workers' Compensation Lloyd's Syndicate Corporate Inter-segment Eliminations Consolidated Net premiums earned $ 116,276 $ 58,407 $ 12,476 $ — $ — $ 187,159 Net investment income — — 751 21,276 — 22,027 Equity in earnings (loss) of unconsolidated subsidiaries — — — 1,640 — 1,640 Net realized gains (losses) — — (54 ) (12,463 ) — (12,517 ) Other income (expense) 1,256 366 331 943 (173 ) 2,723 Net losses and loss adjustment expenses (84,585 ) (36,715 ) (8,486 ) — — (129,786 ) Underwriting, policy acquisition and operating expenses (28,276 ) (17,333 ) (7,246 ) (4,678 ) 173 (57,360 ) Segregated portfolio cells dividend (expense) income 30 (1,894 ) — 117 — (1,747 ) Interest expense — — — (3,705 ) — (3,705 ) Income tax benefit (expense) — — (6 ) 3,428 — 3,422 Segment operating results $ 4,701 $ 2,831 $ (2,234 ) $ 6,558 $ — $ 11,856 Significant non-cash items: Depreciation and amortization, net of accretion $ 1,867 $ 956 $ (1 ) $ 3,257 $ — $ 6,079 Three Months Ended March 31, 2017 (In thousands) Specialty P&C Workers' Compensation Lloyd's Syndicate Corporate Inter-segment Eliminations Consolidated Net premiums earned $ 113,058 $ 55,283 $ 14,562 $ — $ — $ 182,903 Net investment income — — 372 22,814 — 23,186 Equity in earnings (loss) of unconsolidated subsidiaries — — — 1,808 — 1,808 Net realized gains (losses) — — 27 13,253 — 13,280 Other income (expense) 1,198 145 391 173 (86 ) 1,821 Net losses and loss adjustment expenses (74,994 ) (34,650 ) (9,507 ) — — (119,151 ) Underwriting, policy acquisition and operating expenses (25,977 ) (16,691 ) (6,211 ) (8,315 ) 86 (57,108 ) Segregated portfolio cells dividend (expense) income 28 (1,174 ) — (1,229 ) — (2,375 ) Interest expense — — — (4,133 ) — (4,133 ) Income tax benefit (expense) — — 7 1,217 — 1,224 Segment operating results $ 13,313 $ 2,913 $ (359 ) $ 25,588 $ — $ 41,455 Significant non-cash items: Depreciation and amortization, net of accretion $ 1,911 $ 837 $ (3 ) $ 5,058 $ — $ 7,803 The following table provides detailed information regarding ProAssurance's gross premiums earned by product as well as a reconciliation to net premiums earned. All gross premiums earned are from external customers except as noted. ProAssurance's insured risks are primarily within the U.S. Three Months Ended March 31 (In thousands) 2018 2017 Specialty P&C Segment Gross premiums earned: Healthcare professional liability $ 118,685 $ 117,051 Legal professional liability 6,391 6,317 Medical technology liability 8,512 8,312 Other 110 102 Ceded premiums earned (17,422 ) (18,724 ) Segment net premiums earned 116,276 113,058 Workers' Compensation Segment Gross premiums earned: Traditional business 46,030 41,768 Alternative market business 19,381 19,446 Ceded premiums earned (7,004 ) (5,931 ) Segment net premiums earned 58,407 55,283 Lloyd's Syndicate Segment Gross premiums earned: Property and casualty* 17,967 17,185 Ceded premiums earned (5,491 ) (2,623 ) Segment net premiums earned 12,476 14,562 Consolidated net premiums earned $ 187,159 $ 182,903 *Includes premium assumed from the Specialty P&C segment of $1.9 million for the three months ended March 31, 2018 and $3.5 million for the same respective period of 2017 .

Basis of Presentation (Policies

Basis of Presentation (Policies)	3 Months Ended
	Mar. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited Condensed Consolidated Financial Statements include the accounts of ProAssurance Corporation and its consolidated subsidiaries (ProAssurance, PRA or the Company). The financial statements have been prepared in accordance with GAAP for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and notes required by GAAP for complete financial statements. In the opinion of management, all adjustments considered necessary for a fair presentation, consisting of normal recurring adjustments, have been included. ProAssurance’s results for the three months ended March 31, 2018 are not necessarily indicative of the results that may be expected for the year ending December 31, 2018 . The accompanying Condensed Consolidated Financial Statements should be read in conjunction with the Consolidated Financial Statements and Notes contained in ProAssurance’s December 31, 2017 report on Form 10-K. In connection with its preparation of the Condensed Consolidated Financial Statements, ProAssurance evaluated events that occurred subsequent to March 31, 2018 for recognition or disclosure in its financial statements and notes to financial statements. ProAssurance operates in four reportable segments as follows: Specialty P&C , Workers' Compensation, Lloyd's Syndicate and Corporate. For more information on the nature of products and services provided and for financial information by segment, refer to Note 12 .
Reclassifications	Reclassifications In the second quarter of 2017, ProAssurance began presenting separately the components of underwriting, policy acquisition and operating expense as operating expense and DPAC amortization on the Condensed Consolidated Statements of Income and Comprehensive Income in order to provide additional details for investors. The Condensed Consolidated Statements of Income and Comprehensive Income for the three months ended March 31, 2017 have been reclassified to conform to the current period presentation. Total underwriting, policy acquisition and operating expense as well as net income for the three months ended March 31, 2017 was not affected by the change in presentation. Certain other insignificant prior period amounts have been reclassified to conform to the current period presentation.
Accounting Changes Adopted and Not Yet Adopted	Accounting Changes Adopted Restricted Cash ( ASU 2016-18) Effective for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years, the FASB issued guidance related to the classification of restricted cash presented in the statement of cash flows with the objective of reducing diversity in practice. Under the new guidance, entities are required to include restricted cash and restricted cash equivalents with cash and cash equivalents when reconciling beginning-of-period and end-of-period total amounts as presented on the statement of cash flows. ProAssurance adopted the guidance as of January 1, 2018. Adoption of the guidance had no material effect on ProAssurance’s results of operations, financial position or cash flows. Intra-Entity Transfers of Assets Other than Inventory ( ASU 2016-16) Effective for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years, the FASB issued guidance which reduces the complexity in accounting standards related to the income tax consequences of intra-entity transfers of assets other than inventory between tax-paying components. A tax-paying component is an individual entity or group of entities that is consolidated for tax purposes. Under the new guidance, entities are required to recognize income tax consequences of an intra-entity transfer of assets other than inventory when the transfer occurs instead of delaying recognition until the asset has been sold to an outside party. ProAssurance adopted the guidance as of January 1, 2018. Adoption of the guidance had no material effect on ProAssurance’s results of operations, financial position or cash flows. Classification of Certain Cash Receipts and Cash Payments ( ASU 2016-15) Effective for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years, the FASB issued guidance related to the classification of certain cash receipts and cash payments presented in the statement of cash flows with the objective of reducing diversity in practice. ProAssurance adopted the guidance as of January 1, 2018 and elected to use the cumulative earnings approach for presenting distributions from equity method investees. Adoption of the guidance had no material effect on ProAssurance’s results of operations or financial position; however, ProAssurance reclassified approximately $10.9 million in distributions from unconsolidated subsidiaries from investing activities to operating activities in the Condensed Consolidated Statement of Cash Flows for the three months ended March 31, 2017 . Revenue from Contracts with Customers ( ASU 2014-09) Effective for fiscal years beginning after December 15, 2017 the FASB issued guidance related to revenue from contracts with customers. The core principle of the new guidance is that revenue is recognized to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. ProAssurance adopted the guidance as of January 1, 2018 under the modified retrospective method. Adoption of the guidance had no material effect on ProAssurance’s results of operations, financial position or cash flows. Recognition and Measurement of Financial Assets and Financial Liabilities ( ASU 2016-01) Effective for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years, the FASB issued guidance that requires equity investments (except those accounted for under the equity method of accounting, or those that result in consolidation of the investee) to be measured at fair value with changes in fair value recognized in net income. The new guidance also specifies that an entity use the exit price notion when measuring the fair value of financial instruments for disclosure purposes and present financial assets and liabilities by measurement category and form of financial asset. Other provisions of the new guidance include: revised disclosure requirements related to the presentation in comprehensive income of changes in the fair value of liabilities; elimination, for public companies, of disclosure requirements relative to the methods and significant assumptions underlying fair values disclosed for financial instruments measured at amortized cost; and simplified impairment assessments for equity investments without readily determinable fair values. ProAssurance adopted the guidance as of January 1, 2018 using a modified retrospective application and recorded a cumulative-effect after-tax adjustment of approximately $8.3 million to beginning retained earnings in the Condensed Consolidated Statement of Changes in Capital for the three months ended March 31, 2018 . Adoption of the guidance had no material effect on ProAssurance’s results of operations, financial position or cash flows. Modification Accounting for Employee Share-Based Payment Awards ( ASU 2017-09) Effective for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years, the FASB issued guidance which reduces the complexity in accounting standards when there is a change in the terms or conditions of a share-based payment award. The new guidance clarifies that an entity should apply the modification accounting guidance if the value, vesting conditions or classification of the award changes. ProAssurance adopted the guidance as of January 1, 2018. Adoption of the guidance had no material effect on ProAssurance’s results of operations, financial position or cash flows. Reclassification of Certain Tax Effects from AOCI ( ASU 2018-02) Effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years, with early adoption permitted, the FASB issued guidance which permits a reclassification from AOCI to retained earnings for stranded tax effects resulting from the newly enacted federal corporate tax rate from the TCJA . The amount of the reclassification from AOCI to retained earnings will be the difference between the historical corporate tax rate and the newly enacted 21% corporate tax rate on deferred tax items originally established through OCI and not net income. The guidance allows entities to adopt in any interim or annual period for which financial statements have not yet been issued and apply the guidance either (1) in the period of adoption or (2) retrospectively to each period in which the effect of the change in the tax rate is recognized. ProAssurance adopted this guidance as of January 1, 2018 and elected to apply this guidance in the period of adoption using the specific identification method. Using a modified retrospective application, ProAssurance recorded a cumulative-effect adjustment which increased beginning AOCI by approximately $3.4 million and decreased beginning retained earnings by the same amount in the Condensed Consolidated Statement of Changes in Capital for the three months ended March 31, 2018 . Adoption of this guidance had no material effect on ProAssurance's financial position, results of operations or cash flows. Accounting Changes Not Yet Adopted Technical Corrections and Improvements to Financial Instruments - Overall ( ASU 2018-03) Effective for fiscal years beginning after December 15, 2017 and interim periods within those fiscal years beginning after June 15, 2018, the FASB amended the new standard on recognizing and measuring financial assets and financial liabilities to clarify certain aspects of the guidance. Under the amended guidance, an entity that uses the measurement alternative for equity investments without readily determinable fair values can change its measurement approach to a fair value method through an irrevocable election that would apply to that security and all identical or similar investments of the same issuer. Also, entities are required to use the prospective transition approach only for equity investments they elect to measure using the new measurement alternative. Additionally, the guidance clarifies how to apply the measurement alternative and presentation requirements for financial liabilities measured under the fair value option. ProAssurance plans to adopt the guidance beginning July 1, 2018. As of March 31, 2018 , ProAssurance does not have any equity investments without readily determinable fair values or financial liabilities measured under the fair value option; therefore, adoption of the guidance is not expected to have a material effect on ProAssurance’s financial position, results of operations or cash flows. 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 and is currently in the process of evaluating all of its leases. As the majority of ProAssurance's leases are real estate operating leases and are not considered to be material, adoption of the guidance is not expected to have a material effect on ProAssurance’s results of operations, financial position or cash flows. 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 March 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. ProAssurance is in the process of evaluating the effect the new guidance would have on its results of operations and financial position and plans to adopt the guidance beginning January 1, 2020. 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.
Fair Value Policy	The fair values for securities included in the Level 2 category, with the few exceptions described below, were developed by one of several third party, nationally recognized pricing services, including services that price only certain types of securities. Each service uses complex methodologies to determine values for securities and subject the values they develop to quality control reviews. Management selected a primary source for each type of security in the portfolio and reviewed the values provided for reasonableness by comparing data to alternate pricing services and to available market and trade data. Values that appeared inconsistent were further reviewed for appropriateness. Any value that did not appear reasonable was discussed with the service that provided the value and adjusted, if necessary. There were no material changes to the values supplied by the pricing services during the three months ended March 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. Short-term investments were securities maturing within one year, carried at cost which approximated the fair value of the security due to the short term to maturity. 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 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 processes and methodologies used as well as quantitative information regarding securities in the Level 3 category. Level 3 Valuation Processes • Level 3 securities are priced by the Chief Investment Officer. • Level 3 valuations are computed quarterly. Prices are evaluated quarterly against prior period prices and the expected change in prices. • ProAssurance's Level 3 securities are primarily NRSRO rated debt instruments for which comparable market inputs are commonly available for evaluating the securities in question. Valuation of these debt instruments is not overly sensitive to changes in the unobservable inputs used. 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 March 31, 2018 , 87% 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 March 31, 2018 , 78% 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 March 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.

Basis of Presentation (Tables)

Basis of Presentation (Tables)	3 Months Ended
	Mar. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Other Liabilities	Other liabilities consisted of the following: (In thousands) March 31, 2018 December 31, 2017 SPC dividends payable $ 47,122 $ 46,925 Unpaid dividends 16,616 267,292 All other 144,128 123,383 Total other liabilities $ 207,866 $ 437,600

Fair Value Measurement (Tables)

Fair Value Measurement (Tables)	3 Months Ended
	Mar. 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 March 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. March 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 $ — $ 129,751 $ — $ 129,751 U.S. Government-sponsored enterprise obligations — 29,959 — 29,959 State and municipal bonds — 329,995 — 329,995 Corporate debt, multiple observable inputs 2,334 1,230,832 — 1,233,166 Corporate debt, limited observable inputs — — 15,097 15,097 Residential mortgage-backed securities — 215,420 — 215,420 Agency commercial mortgage-backed securities — 14,887 — 14,887 Other commercial mortgage-backed securities — 29,195 — 29,195 Other asset-backed securities — 138,890 17,323 156,213 Fixed maturities, trading Corporate debt — 4,148 — 4,148 Equity investments Financial 74,556 — — 74,556 Utilities/Energy 46,637 — — 46,637 Consumer oriented 54,789 — — 54,789 Industrial 48,859 — — 48,859 Bond funds 153,256 — — 153,256 All other 93,847 — — 93,847 Short-term investments 288,019 61,100 — 349,119 Other investments 604 32,073 365 33,042 Other assets — 2,306 — 2,306 Total assets categorized within the fair value hierarchy $ 762,901 $ 2,218,556 $ 32,785 3,014,242 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 20,215 Investment in unconsolidated subsidiaries 277,094 Total assets at fair value $ 3,311,551 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) March 31, 2018 December 31, 2017 Valuation Technique Unobservable Input Range Assets: Corporate debt, limited observable inputs $15,097 $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 $17,323 $4,986 Market Comparable Comparability Adjustment 0% - 5% (2.5%) Discounted Cash Flows Comparability Adjustment 0% - 5% (2.5%) Other investments $365 $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. March 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 (38 ) — — (38 ) Net realized investment gains (losses) — — (44 ) (44 ) Included in other comprehensive income (38 ) (30 ) — (68 ) Purchases 6,005 13,453 — 19,458 Sales (2,905 ) (27 ) — (2,932 ) Transfers in 2,069 — — 2,069 Transfers out (3,699 ) (1,059 ) — (4,758 ) Balance March 31, 2018 $ 15,097 $ 17,323 $ 365 $ 32,785 Change in unrealized gains (losses) included in earnings for the above period for Level 3 assets held at period-end $ — $ — $ — $ — March 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 (39 ) — — (39 ) Net realized investment gains (losses) 13 — — 13 Included in other comprehensive income (208 ) (5 ) 2 (211 ) Purchases 7,048 — — 7,048 Sales (1,712 ) — — (1,712 ) Transfers in — — 898 898 Transfers out (998 ) — — (998 ) Balance March 31, 2017 $ 18,914 $ 3,002 $ 903 $ 22,819 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	At March 31, 2018 and December 31, 2017 , certain LP s/ LLC s and investment funds measure fund assets at fair value on a recurring basis and provide a NAV for ProAssurance's interest. The carrying value of these interests is based on the NAV provided and was considered to approximate the fair value of the interests. For investment in unconsolidated subsidiaries, ProAssurance recognizes any changes in the NAV of its interests in equity in earnings (loss) of unconsolidated subsidiaries during the period of change. In accordance with GAAP , the fair value of these investments was not classified within the fair value hierarchy. The amount of ProAssurance's unfunded commitments related to these investments as of March 31, 2018 and fair values of these investments as of March 31, 2018 and December 31, 2017 was as follows: Unfunded Fair Value (In thousands) March 31, March 31, December 31, Equity investments: Mortgage fund (1)* None $ 20,215 $ — Investment in unconsolidated subsidiaries: Private debt funds (2) $4,976 32,064 42,206 Long equity fund (3) None 7,957 7,847 Long/short equity funds (4) None 32,177 31,352 Non-public equity funds (5) $82,135 105,049 100,062 Multi-strategy fund of funds (6) None 9,274 9,100 Credit funds (7) None 17,789 6,561 Long/short commodities fund (8) None 13,063 13,025 Strategy focused funds (9) $19,241 59,721 606 277,094 210,759 Other investments: Mortgage fund (1)* See above — 20,130 Total investments carried at NAV $ 297,309 $ 230,889 * In the first quarter of 2018, ProAssurance began presenting this investment previously reported as a part of other investments as a part of equity investments on the Condensed Consolidated Balance Sheet as of March 31, 2018. Prior year amounts have not been reclassified. Below is additional information regarding each of the investments listed in the table above as of March 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) The investment is comprised of interests in two 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 does not permit redemption. Income and capital are to be periodically distributed at the discretion of the LP s over an anticipated time frame that spans from three to eight years. (3) The fund is a LP that holds long equities of public international companies. Redemptions are allowed at the end of any calendar month with a prior notice requirement of 15 days and are paid within 10 days of the end of the calendar month of the redemption request. (4) The investment is comprised of interests in multiple unrelated LP funds. The funds hold primarily long and short North American equities and target absolute returns using strategies designed to take advantage of market opportunities. The funds generally permit quarterly or semi-annual capital redemptions subject to notice requirements of 30 to 90 days . For some funds, redemptions above specified thresholds (lowest threshold is 90% ) may be only partially payable until after a fund audit is completed and are then payable within 30 days . (5) The investment is comprised of interests in multiple unrelated LP funds, each structured to provide capital appreciation through diversified investments in private equity, which can include investments in buyout, venture capital, debt including senior, second lien and mezzanine, distressed debt and other private equity-oriented LP s. Two of the LP s allow redemption by terms set forth in the LP agreements; the others do not permit redemption. Income and capital are to be periodically distributed at the discretion of the LP over time frames that are anticipated to span up to nine years. (6) This fund is a LLC structured to build and manage low volatility, multi-manager portfolios that have little or no correlation to the broader fixed income and equity security markets. Redemptions are not permitted but offers to repurchase units of the LLC may be extended periodically. (7) The investment is comprised of two unrelated LP funds. One fund seeks to obtain superior risk-adjusted absolute returns through a diversified portfolio of debt securities, including bonds, loans and other asset-backed instruments. The second fund seeks event driven opportunities across the corporate credit spectrum. For both funds, redemptions are allowed at any quarter-end with a prior notice requirement of 90 days . (8) This fund is a LLC invested across a broad range of commodities and focuses primarily on market neutral, relative value strategies, seeking to generate absolute returns with low correlation to broad commodity, equity and fixed income markets. Following an initial one-year lock-up period, redemptions are allowed with a prior notice requirement of 30 days and are payable within 30 days . (9) The investment is comprised of multiple unrelated LP funds. One fund is a LLC focused on investing in North American consumer products companies, comprised of equity and equity-related securities, as well as debt instruments. Redemptions are not permitted. Another fund is a LP focused on North American energy infrastructure assets that allows redemption with consent of the General Partner. The remaining funds are real estate focused LP s, one of which allows for redemption with prior notice.
Financial instruments not measured at fair value	The following table provides the estimated fair value of our financial instruments that, in accordance with GAAP for the type of investment, are measured using a methodology other than fair value. All fair values provided primarily fall within the Level 3 fair value category. March 31, 2018 December 31, 2017 (In thousands) Carrying Fair Carrying Fair Financial assets: BOLI $ 62,562 $ 62,562 $ 62,113 $ 62,113 Other investments $ 2,902 $ 2,902 $ 58,546 $ 69,095 Other assets $ 49,549 $ 48,816 $ 34,020 $ 33,742 Financial liabilities: Senior notes due 2023* $ 250,000 $ 269,418 $ 250,000 $ 273,153 Revolving Credit Agreement* $ 83,000 $ 83,000 $ 123,000 $ 123,000 Mortgage loans* $ 40,111 $ 40,111 $ 40,460 $ 40,460 Other liabilities $ 21,525 $ 21,525 $ 21,154 $ 21,154 * Carrying value excludes debt issuance costs.

Investments (Tables)

Investments (Tables)	3 Months Ended
	Mar. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Amortized cost and estimated fair value of available-for-sale fixed maturities and equity securities	Available-for-sale fixed maturities at March 31, 2018 and December 31, 2017 included the following: March 31, 2018 (In thousands) Amortized Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Fixed maturities, available for sale U.S. Treasury obligations $ 131,655 $ 305 $ 2,209 $ 129,751 U.S. Government-sponsored enterprise obligations 30,377 27 445 29,959 State and municipal bonds 324,336 6,613 954 329,995 Corporate debt 1,259,132 7,008 17,877 1,248,263 Residential mortgage-backed securities 217,891 1,502 3,973 215,420 Agency commercial mortgage-backed securities 15,078 29 220 14,887 Other commercial mortgage-backed securities 29,409 100 314 29,195 Other asset-backed securities 157,506 40 1,333 156,213 $ 2,165,384 $ 15,624 $ 27,325 $ 2,153,683 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 March 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 $ 131,655 $ 31,700 $ 73,858 $ 21,321 $ 2,872 $ 129,751 U.S. Government-sponsored enterprise obligations 30,377 — 8,009 21,814 136 29,959 State and municipal bonds 324,336 29,481 111,512 140,004 48,998 329,995 Corporate debt 1,259,132 115,385 682,646 404,159 46,073 1,248,263 Residential mortgage-backed securities 217,891 215,420 Agency commercial mortgage-backed securities 15,078 14,887 Other commercial mortgage-backed securities 29,409 29,195 Other asset-backed securities 157,506 156,213 $ 2,165,384 $ 2,153,683
Investments held in an unrealized loss position	The following tables provide summarized information with respect to investments held in an unrealized loss position at March 31, 2018 and December 31, 2017 , including the length of time the investment had been held in a continuous unrealized loss position. March 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 $ 121,718 $ 2,209 $ 87,740 $ 1,438 $ 33,978 $ 771 U.S. Government-sponsored enterprise obligations 29,018 445 22,252 218 6,766 227 State and municipal bonds 63,690 954 55,761 620 7,929 334 Corporate debt 848,499 17,877 733,344 13,216 115,155 4,661 Residential mortgage-backed securities 175,295 3,973 132,075 2,066 43,220 1,907 Agency commercial mortgage-backed securities 9,547 220 7,638 101 1,909 119 Other commercial mortgage-backed securities 19,145 314 15,723 256 3,422 58 Other asset-backed securities 118,780 1,333 105,370 1,134 13,410 199 $ 1,385,692 $ 27,325 $ 1,159,903 $ 19,049 $ 225,789 $ 8,276 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
Information regarding sales and purchases of available-for-sale securities	Other information regarding sales and purchases of fixed maturity available-for-sale securities is as follows: Three Months Ended March 31 (In millions) 2018 2017 Proceeds from sales (exclusive of maturities and paydowns) $ 379.2 $ 79.2 Purchases $ 367.9 $ 160.4
Net Investment Income	Net investment income by investment category was as follows: Three Months Ended (In thousands) 2018 2017 Fixed maturities $ 17,080 $ 20,121 Equities 4,867 3,644 Short-term investments, including Other 1,308 801 BOLI 449 455 Investment fees and expenses (1,677 ) (1,835 ) Net investment income $ 22,027 $ 23,186
Investments in unconsolidated subsidiaries	ProAssurance's investment in unconsolidated subsidiaries were as follows: March 31, 2018 Carrying Value (In thousands) Percentage March 31, December 31, Qualified affordable housing project tax credit partnerships See below $ 80,507 $ 84,607 Other tax credit partnerships See below 5,735 6,118 All other investments, primarily investment fund LPs/LLCs See below 314,788 239,866 $ 401,030 $ 330,591
Net realized investment gains (losses)	Realized investment gains and losses are recognized on the first-in, first-out basis. The following table provides detailed information regarding net realized investment gains (losses): Three Months Ended (In thousands) 2018 2017 Total OTTI losses: Corporate debt $ — $ (419 ) Portion of OTTI losses recognized in other comprehensive income before taxes: Corporate debt — 248 Net impairment losses recognized in earnings — (171 ) Gross realized gains, available-for-sale fixed maturities 4,464 1,853 Gross realized (losses), available-for-sale fixed maturities (2,047 ) (67 ) Net realized gains (losses), equity investments 9,219 6,562 Net realized gains (losses), other investments 688 1,172 Change in unrealized holding gains (losses), trading fixed maturities (49 ) — Change in unrealized holding gains (losses), equity investments (23,845 ) 3,616 Change in unrealized holding gains (losses), convertible securities, carried at fair value (954 ) 313 Other 7 2 Net realized investment gains (losses) $ (12,517 ) $ 13,280
Other than temporary impairment, credit losses recognized in earnings	The following table presents a roll forward of cumulative credit losses recorded in earnings related to impaired debt securities for which a portion of the OTTI was recorded in OCI . Three Months Ended March 31 (In thousands) 2018 2017 Balance beginning of period $ 1,313 $ 1,158 Additional credit losses recognized during the period, related to securities for which: No OTTI has been previously recognized — 171 Balance March 31 $ 1,313 $ 1,329

Reserve for Losses and Loss A23

Reserve for Losses and Loss Adjustment Expenses (Tables)	3 Months Ended
	Mar. 31, 2018
Insurance [Abstract]
Summary of reserve for losses and loss adjustment expenses	Activity in the reserve for losses and loss adjustment expenses is summarized as follows: (In thousands) Three Months Ended March 31, 2018 Three Months Ended March 31, 2017 Year Ended December 31, 2017 Balance, beginning of year $ 2,048,381 $ 1,993,428 $ 1,993,428 Less reinsurance recoverables on unpaid losses and loss adjustment expenses 335,585 273,475 273,475 Net balance, beginning of year 1,712,796 1,719,953 1,719,953 Net losses: Current year 152,572 147,927 603,518 Favorable development of reserves established in prior years, net (22,786 ) (28,776 ) (134,360 ) Total 129,786 119,151 469,158 Paid related to: Current year (14,243 ) (33,085 ) (106,633 ) Prior years (101,078 ) (80,709 ) (369,682 ) Total paid (115,321 ) (113,794 ) (476,315 ) Net balance, end of period 1,727,261 1,725,310 1,712,796 Plus reinsurance recoverables on unpaid losses and loss adjustment expenses 329,540 271,679 335,585 Balance, end of period $ 2,056,801 $ 1,996,989 $ 2,048,381

Debt (Tables)

Debt (Tables)	3 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
Schedule of Long-term Debt Instruments	ProAssurance’s outstanding debt consisted of the following: (In thousands) March 31, December 31, Senior Notes due 2023, unsecured, interest at 5.3% annually $ 250,000 $ 250,000 Revolving Credit Agreement, outstanding borrowings are fully secured, see Note 3, and carried at a weighted average interest rate of 2.24% and 1.91%, respectively. Outstanding borrowings are not permitted to exceed $250 million aggregately; Revolving Credit Agreement expires in 2020. The interest rate on the borrowings is set at the time the respective borrowing is initiated or renewed. The current borrowing can be repaid or renewed in the second quarter of 2018. If renewed, the interest rate will be reset. 83,000 123,000 Mortgage Loans, outstanding borrowings are secured by first priority liens on two office buildings, and bear an interest rate of three-month LIBOR plus 1.325% (3.42% and 2.86%, respectively) determined on a quarterly basis. 40,111 40,460 Total principal 373,111 413,460 Less debt issuance costs 1,583 1,649 Debt less debt issuance costs $ 371,528 $ 411,811

Derivatives (Tables)

Derivatives (Tables)	3 Months Ended
	Mar. 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 Condensed Consolidated Balance Sheets as of March 31, 2018 and December 31, 2017 . ($ in thousands) March 31, 2018 December 31, 2017 Derivatives Not Designated as Hedging Instruments Location in the Condensed Consolidated Balance Sheets Number of Instruments Notional Amount (1) Estimated Fair Value (2) Number of Instruments Notional Amount (1) Estimated Fair Value (2) Interest Rate Cap Other assets 1 $ 35,000 $ 2,306 1 $ 35,000 $ 1,731 (1) Volume is represented by the derivative instrument's notional amount. (2) Additional information regarding the fair value of the Company's interest rate cap is provided in Note 2. The following table presents the pre-tax impact of the change in the fair value of the interest rate cap and the reporting location in the Condensed Consolidated Statements of Income and Comprehensive Income for the three months ended March 31, 2018 and 2017 . Gains (Losses) Recognized in Income on Derivatives (In thousands) Three Months Ended March 31 Derivatives Not Designated as Hedging Instruments Location in the Condensed Consolidated Statements of Income and Comprehensive Income 2018 2017 Interest Rate Cap Interest expense $ 575 $ —

Shareholders' Equity (Tables)

Shareholders' Equity (Tables)	3 Months Ended
	Mar. 31, 2018
Equity [Abstract]
Schedule of Share-based compensation expense and related tax benefits	Share-based compensation expense and related tax benefits were as follows: Three Months Ended March 31 (In thousands) 2018 2017 Share-based compensation expense $ 902 $ 3,346 Related tax benefits $ 190 $ 1,171
Reclassification adjustments related to available-for-sale securities	Amounts reclassified from AOCI to net income and the amounts of deferred tax expense (benefit) included in OCI were as follows: Three Months Ended March 31 (In thousands) 2018 2017 Reclassifications from AOCI to net income: Realized investment gains (losses) $ 2,417 $ 1,616 Tax effect* (508 ) (566 ) Net reclassification adjustments $ 1,909 $ 1,050 Deferred tax expense (benefit) included in OCI $ (7,060 ) $ 1,481 * Tax effects were computed using a 21% and 35% rate for the three months ended March 31, 2018 and 2017, respectively.

Earnings Per Share (Tables)

Earnings Per Share (Tables)	3 Months Ended
	Mar. 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) Three Months Ended March 31 2018 2017 Weighted average number of common shares outstanding, basic 53,515 53,315 Dilutive effect of securities: Restricted Share Units 82 78 Performance Share Units 66 121 Purchase Match Units 19 21 Weighted average number of common shares outstanding, diluted 53,682 53,535 Effect of dilutive shares on earnings per share $ — $ (0.01 )

Segment Information (Tables)

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2018
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment	Financial results by segment were as follows: Three Months Ended March 31, 2018 (In thousands) Specialty P&C Workers' Compensation Lloyd's Syndicate Corporate Inter-segment Eliminations Consolidated Net premiums earned $ 116,276 $ 58,407 $ 12,476 $ — $ — $ 187,159 Net investment income — — 751 21,276 — 22,027 Equity in earnings (loss) of unconsolidated subsidiaries — — — 1,640 — 1,640 Net realized gains (losses) — — (54 ) (12,463 ) — (12,517 ) Other income (expense) 1,256 366 331 943 (173 ) 2,723 Net losses and loss adjustment expenses (84,585 ) (36,715 ) (8,486 ) — — (129,786 ) Underwriting, policy acquisition and operating expenses (28,276 ) (17,333 ) (7,246 ) (4,678 ) 173 (57,360 ) Segregated portfolio cells dividend (expense) income 30 (1,894 ) — 117 — (1,747 ) Interest expense — — — (3,705 ) — (3,705 ) Income tax benefit (expense) — — (6 ) 3,428 — 3,422 Segment operating results $ 4,701 $ 2,831 $ (2,234 ) $ 6,558 $ — $ 11,856 Significant non-cash items: Depreciation and amortization, net of accretion $ 1,867 $ 956 $ (1 ) $ 3,257 $ — $ 6,079 Three Months Ended March 31, 2017 (In thousands) Specialty P&C Workers' Compensation Lloyd's Syndicate Corporate Inter-segment Eliminations Consolidated Net premiums earned $ 113,058 $ 55,283 $ 14,562 $ — $ — $ 182,903 Net investment income — — 372 22,814 — 23,186 Equity in earnings (loss) of unconsolidated subsidiaries — — — 1,808 — 1,808 Net realized gains (losses) — — 27 13,253 — 13,280 Other income (expense) 1,198 145 391 173 (86 ) 1,821 Net losses and loss adjustment expenses (74,994 ) (34,650 ) (9,507 ) — — (119,151 ) Underwriting, policy acquisition and operating expenses (25,977 ) (16,691 ) (6,211 ) (8,315 ) 86 (57,108 ) Segregated portfolio cells dividend (expense) income 28 (1,174 ) — (1,229 ) — (2,375 ) Interest expense — — — (4,133 ) — (4,133 ) Income tax benefit (expense) — — 7 1,217 — 1,224 Segment operating results $ 13,313 $ 2,913 $ (359 ) $ 25,588 $ — $ 41,455 Significant non-cash items: Depreciation and amortization, net of accretion $ 1,911 $ 837 $ (3 ) $ 5,058 $ — $ 7,803
Schedule of Gross Premiums by Product	The following table provides detailed information regarding ProAssurance's gross premiums earned by product as well as a reconciliation to net premiums earned. All gross premiums earned are from external customers except as noted. ProAssurance's insured risks are primarily within the U.S. Three Months Ended March 31 (In thousands) 2018 2017 Specialty P&C Segment Gross premiums earned: Healthcare professional liability $ 118,685 $ 117,051 Legal professional liability 6,391 6,317 Medical technology liability 8,512 8,312 Other 110 102 Ceded premiums earned (17,422 ) (18,724 ) Segment net premiums earned 116,276 113,058 Workers' Compensation Segment Gross premiums earned: Traditional business 46,030 41,768 Alternative market business 19,381 19,446 Ceded premiums earned (7,004 ) (5,931 ) Segment net premiums earned 58,407 55,283 Lloyd's Syndicate Segment Gross premiums earned: Property and casualty* 17,967 17,185 Ceded premiums earned (5,491 ) (2,623 ) Segment net premiums earned 12,476 14,562 Consolidated net premiums earned $ 187,159 $ 182,903 *Includes premium assumed from the Specialty P&C segment of $1.9 million for the three months ended March 31, 2018 and $3.5 million for the same respective period of 2017 .

Basis of Presentation (Narrativ

Basis of Presentation (Narrative) (Details) $ in Thousands		3 Months Ended
		Mar. 31, 2018USD ($)segment	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of reportable segments | segment		4
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other liabilities		$ 207,866		$ 437,600
Distributed earnings from unconsolidated subsidiaries		7,018	$ 10,893
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification from AOCI to retained earnings for stranded tax effects		(3,400)
Accumulated Other Comprehensive Income (Loss)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification from AOCI to retained earnings for stranded tax effects		$ 3,400
Accounting Standards Update 2016-15
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Distributions from unconsolidated subsidiaries, investing activities			(10,900)
Distributed earnings from unconsolidated subsidiaries			$ 10,900
Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative-effect adjustment adoption of ASU	[1]			8,334
Accounting Standards Update 2016-01 | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative-effect adjustment adoption of ASU	[1]			$ 8,334
[1]	See Note 1 for discussion of accounting guidance adopted during the period.

Basis of Presentation (Other Li

Basis of Presentation (Other Liabilities) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
SPC dividends payable	$ 47,122	$ 46,925
Unpaid dividends	16,616	267,292	$ 16,516
All other	144,128	123,383
Total other liabilities	$ 207,866	$ 437,600

Fair Value Measurement (Assets

Fair Value Measurement (Assets and Liabilities Measured at Fair Value) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Assets:
Fixed maturities, available for sale	$ 2,153,683	$ 2,280,242
Equity investments	492,159	470,609
Fair Value	297,309	230,889
Investment in unconsolidated subsidiaries
Assets:
Fair Value	277,094	210,759
Level 3 | Corporate debt, limited observable inputs
Assets:
Total assets categorized within the fair value hierarchy	15,097	13,703
Level 3 | Other investments
Assets:
Total assets categorized within the fair value hierarchy	365	409
Recurring
Assets:
Other assets	2,306	1,731
Total assets categorized within the fair value hierarchy	3,014,242	3,216,879
Total assets at fair value	3,311,551	3,447,768
Recurring | U.S. Treasury obligations
Assets:
Fixed maturities, available for sale	129,751	133,627
Recurring | U.S. Government-sponsored enterprise obligations
Assets:
Fixed maturities, available for sale	29,959	20,956
Recurring | State and municipal bonds
Assets:
Fixed maturities, available for sale	329,995	632,243
Recurring | Corporate debt, multiple observable inputs
Assets:
Fixed maturities, available for sale	1,233,166	1,153,455
Recurring | Corporate debt, limited observable inputs
Assets:
Fixed maturities, available for sale	15,097	13,703
Recurring | Residential mortgage-backed securities
Assets:
Fixed maturities, available for sale	215,420	197,844
Recurring | Agency commercial mortgage-backed securities
Assets:
Fixed maturities, available for sale	14,887	10,742
Recurring | Other commercial mortgage-backed securities
Assets:
Fixed maturities, available for sale	29,195	15,961
Recurring | Other asset-backed securities
Assets:
Fixed maturities, available for sale	156,213	101,711
Recurring | Corporate Debt
Assets:
Fixed maturities, available for sale	4,148
Recurring | Financial
Assets:
Equity investments	74,556	76,051
Recurring | Utilities/Energy
Assets:
Equity investments	46,637	54,388
Recurring | Consumer oriented
Assets:
Equity investments	54,789	54,529
Recurring | Industrial
Assets:
Equity investments	48,859	53,936
Recurring | Bond funds
Assets:
Equity investments	153,256	156,563
Recurring | All other
Assets:
Equity investments	93,847	75,142
Recurring | Short-term investments
Assets:
Short-term and other investments	349,119	432,126
Recurring | Other investments
Assets:
Short-term and other investments	33,042	32,171
Fair Value		20,130
Recurring | Investment in unconsolidated subsidiaries
Assets:
Fair Value		210,759
Recurring | Level 1
Assets:
Other assets	0	0
Total assets categorized within the fair value hierarchy	762,901	877,791
Recurring | Level 1 | U.S. Treasury obligations
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 1 | U.S. Government-sponsored enterprise obligations
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 1 | State and municipal bonds
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 1 | Corporate debt, multiple observable inputs
Assets:
Fixed maturities, available for sale	2,334	2,371
Recurring | Level 1 | Corporate debt, limited observable inputs
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 1 | Residential mortgage-backed securities
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 1 | Agency commercial mortgage-backed securities
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 1 | Other commercial mortgage-backed securities
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 1 | Other asset-backed securities
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 1 | Corporate Debt
Assets:
Fixed maturities, available for sale	0
Recurring | Level 1 | Financial
Assets:
Equity investments	74,556	76,051
Recurring | Level 1 | Utilities/Energy
Assets:
Equity investments	46,637	54,388
Recurring | Level 1 | Consumer oriented
Assets:
Equity investments	54,789	54,529
Recurring | Level 1 | Industrial
Assets:
Equity investments	48,859	53,936
Recurring | Level 1 | Bond funds
Assets:
Equity investments	153,256	156,563
Recurring | Level 1 | All other
Assets:
Equity investments	93,847	75,142
Recurring | Level 1 | Short-term investments
Assets:
Short-term and other investments	288,019	404,204
Recurring | Level 1 | Other investments
Assets:
Short-term and other investments	604	607
Recurring | Level 2
Assets:
Other assets	2,306	1,731
Total assets categorized within the fair value hierarchy	2,218,556	2,319,990
Recurring | Level 2 | U.S. Treasury obligations
Assets:
Fixed maturities, available for sale	129,751	133,627
Recurring | Level 2 | U.S. Government-sponsored enterprise obligations
Assets:
Fixed maturities, available for sale	29,959	20,956
Recurring | Level 2 | State and municipal bonds
Assets:
Fixed maturities, available for sale	329,995	632,243
Recurring | Level 2 | Corporate debt, multiple observable inputs
Assets:
Fixed maturities, available for sale	1,230,832	1,151,084
Recurring | Level 2 | Corporate debt, limited observable inputs
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 2 | Residential mortgage-backed securities
Assets:
Fixed maturities, available for sale	215,420	196,789
Recurring | Level 2 | Agency commercial mortgage-backed securities
Assets:
Fixed maturities, available for sale	14,887	10,742
Recurring | Level 2 | Other commercial mortgage-backed securities
Assets:
Fixed maturities, available for sale	29,195	15,961
Recurring | Level 2 | Other asset-backed securities
Assets:
Fixed maturities, available for sale	138,890	97,780
Recurring | Level 2 | Corporate Debt
Assets:
Fixed maturities, available for sale	4,148
Recurring | Level 2 | Financial
Assets:
Equity investments	0	0
Recurring | Level 2 | Utilities/Energy
Assets:
Equity investments	0	0
Recurring | Level 2 | Consumer oriented
Assets:
Equity investments	0	0
Recurring | Level 2 | Industrial
Assets:
Equity investments	0	0
Recurring | Level 2 | Bond funds
Assets:
Equity investments	0	0
Recurring | Level 2 | All other
Assets:
Equity investments	0	0
Recurring | Level 2 | Short-term investments
Assets:
Short-term and other investments	61,100	27,922
Recurring | Level 2 | Other investments
Assets:
Short-term and other investments	32,073	31,155
Recurring | Level 3
Assets:
Other assets	0	0
Total assets categorized within the fair value hierarchy	32,785	19,098
Recurring | Level 3 | U.S. Treasury obligations
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 3 | U.S. Government-sponsored enterprise obligations
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 3 | State and municipal bonds
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 3 | Corporate debt, multiple observable inputs
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 3 | Corporate debt, limited observable inputs
Assets:
Fixed maturities, available for sale	15,097	13,703
Recurring | Level 3 | Residential mortgage-backed securities
Assets:
Fixed maturities, available for sale	0	1,055
Recurring | Level 3 | Agency commercial mortgage-backed securities
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 3 | Other commercial mortgage-backed securities
Assets:
Fixed maturities, available for sale	0	0
Recurring | Level 3 | Other asset-backed securities
Assets:
Fixed maturities, available for sale	17,323	3,931
Recurring | Level 3 | Corporate Debt
Assets:
Fixed maturities, available for sale	0
Recurring | Level 3 | Financial
Assets:
Equity investments	0	0
Recurring | Level 3 | Utilities/Energy
Assets:
Equity investments	0	0
Recurring | Level 3 | Consumer oriented
Assets:
Equity investments	0	0
Recurring | Level 3 | Industrial
Assets:
Equity investments	0	0
Recurring | Level 3 | Bond funds
Assets:
Equity investments	0	0
Recurring | Level 3 | All other
Assets:
Equity investments	0	0
Recurring | Level 3 | Short-term investments
Assets:
Short-term and other investments	0	0
Recurring | Level 3 | Other investments
Assets:
Short-term and other investments	365	409
Mortgage fund | Other investments
Assets:
Fair Value	0	20,130
Mortgage fund | Equities
Assets:
Fair Value	$ 20,215	$ 0

Fair Value Measurement (Narrati

Fair Value Measurement (Narrative) (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018USD ($)Agreement	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)
Credit Derivatives [Line Items]
Transfer of equity securities from Level 2 to Level 1		$ 35,400
Net impairment losses recognized in earnings	$ 0	$ 171
Fair value of funded deferred compensation assets	$ 21,600		$ 20,200
Number of line of credit agreement | Agreement	2
Assets, Fair Value Disclosure, Nonrecurring			$ 1,200
Corporate debt, limited observable inputs | NRSRO | NRSRO, Rating BBB
Credit Derivatives [Line Items]
Credit rating	87.00%
Corporate debt, limited observable inputs | NRSRO | NRSRO, Rating BBBplus
Credit Derivatives [Line Items]
Credit rating			84.00%
Residential mortgage-backed and other asset-backed securities | NRSRO | NRSRO, Rating AAA
Credit Derivatives [Line Items]
Credit rating	78.00%		21.00%
Equities
Credit Derivatives [Line Items]
Transfer of equity securities from Level 2 to Level 1	$ 0
Early Stage Business Development | Investment in unconsolidated subsidiaries
Credit Derivatives [Line Items]
Net impairment losses recognized in earnings			$ 8,500

Fair Value Measurement (Quantit

Fair Value Measurement (Quantitative Information Regarding Level 3 Valuations) (Details) - Level 3 - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Corporate debt, limited observable inputs
Assets:
Fair Value at	$ 15,097	$ 13,703
Corporate debt, limited observable inputs | Market Comparable Securities | Minimum
Assets:
Comparability Adjustment	0.00%
Corporate debt, limited observable inputs | Market Comparable Securities | Maximum
Assets:
Comparability Adjustment	5.00%
Corporate debt, limited observable inputs | Market Comparable Securities | Weighted Average
Assets:
Comparability Adjustment	2.50%
Corporate debt, limited observable inputs | Discounted Cash Flows | Minimum
Assets:
Comparability Adjustment	0.00%
Corporate debt, limited observable inputs | Discounted Cash Flows | Maximum
Assets:
Comparability Adjustment	5.00%
Corporate debt, limited observable inputs | Discounted Cash Flows | Weighted Average
Assets:
Comparability Adjustment	2.50%
Residential mortgage-backed and other asset-backed securities
Assets:
Fair Value at	$ 17,323	4,986
Residential mortgage-backed and other asset-backed securities | Market Comparable Securities | Minimum
Assets:
Comparability Adjustment	0.00%
Residential mortgage-backed and other asset-backed securities | Market Comparable Securities | Maximum
Assets:
Comparability Adjustment	5.00%
Residential mortgage-backed and other asset-backed securities | Market Comparable Securities | Weighted Average
Assets:
Comparability Adjustment	2.50%
Residential mortgage-backed and other asset-backed securities | Discounted Cash Flows | Minimum
Assets:
Comparability Adjustment	0.00%
Residential mortgage-backed and other asset-backed securities | Discounted Cash Flows | Maximum
Assets:
Comparability Adjustment	5.00%
Residential mortgage-backed and other asset-backed securities | Discounted Cash Flows | Weighted Average
Assets:
Comparability Adjustment	2.50%
Other investments
Assets:
Fair Value at	$ 365	$ 409
Other investments | Discounted Cash Flows | Minimum
Assets:
Comparability Adjustment	0.00%
Other investments | Discounted Cash Flows | Maximum
Assets:
Comparability Adjustment	10.00%
Other investments | Discounted Cash Flows | Weighted Average
Assets:
Comparability Adjustment	5.00%

Fair Value Measurement (Level 3

Fair Value Measurement (Level 3 Assets) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation:
Beginning Balance	$ 19,098	$ 17,820
Included in earnings, as a part of:
Included in other comprehensive income	(68)	(211)
Purchases	19,458	7,048
Sales	(2,932)	(1,712)
Transfers in	2,069	898
Transfers out	(4,758)	(998)
Ending Balance	32,785	22,819
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
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	(38)	(39)
Net realized investment gains (losses)
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	(44)	13
Corporate Debt
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation:
Beginning Balance	13,703	14,810
Included in earnings, as a part of:
Included in other comprehensive income	(38)	(208)
Purchases	6,005	7,048
Sales	(2,905)	(1,712)
Transfers in	2,069	0
Transfers out	(3,699)	(998)
Ending Balance	15,097	18,914
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
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	(38)	(39)
Corporate Debt | Net realized investment gains (losses)
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	0	13
Asset-backed Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation:
Beginning Balance	4,986	3,007
Included in earnings, as a part of:
Included in other comprehensive income	(30)	(5)
Purchases	13,453	0
Sales	(27)	0
Transfers in	0	0
Transfers out	(1,059)	0
Ending Balance	17,323	3,002
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
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	0	0
Asset-backed Securities | Net realized investment gains (losses)
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	0	0
Other investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation:
Beginning Balance	409	3
Included in earnings, as a part of:
Included in other comprehensive income	0	2
Purchases	0	0
Sales	0	0
Transfers in	0	898
Transfers out	0	0
Ending Balance	365	903
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
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	0	0
Other investments | Net realized investment gains (losses)
Included in earnings, as a part of:
Total gains (losses) realized and unrealized, included in earnings	$ (44)	$ 0

Fair Value Measurement (Investm

Fair Value Measurement (Investments in LLCs and Limited Partnerships) (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	$ 297,309,000	$ 230,889,000
Equities | Mortgage fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Commitments	0
Fair Value	20,215,000	0
Investment in unconsolidated subsidiaries
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	277,094,000	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	4,976,000
Fair Value	32,064,000	42,206,000
Investment in unconsolidated subsidiaries | Long equity fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Commitments	0
Fair Value	7,957,000	7,847,000
Investment in unconsolidated subsidiaries | Long/short equity funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Commitments	0
Fair Value	32,177,000	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	82,135,000
Fair Value	105,049,000	100,062,000
Investment in unconsolidated subsidiaries | Multi-strategy fund of funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Commitments	0
Fair Value	9,274,000	9,100,000
Investment in unconsolidated subsidiaries | Credit fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Commitments	0
Fair Value	17,789,000	6,561,000
Investment in unconsolidated subsidiaries | Long/short commodities fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded Commitments	0
Fair Value	13,063,000	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	19,241,000
Fair Value	59,721,000	606,000
Other investments | Mortgage fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	$ 0	$ 20,130,000

Fair Value Measurement (Inves36

Fair Value Measurement (Investments in LLCs and Limited Partnerships Footnote) (Details)	3 Months Ended
	Mar. 31, 2018
Mortgage fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investment redemption notice period	65 days
Payment period for redemption of LP valued at NAV	45 days
Long equity fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investment redemption notice period	15 days
Payment period for redemption of LP valued at NAV	10 days
Long/short equity funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Payment period for redemption of LP valued at NAV	30 days
Redemption percentage of LP at NAV for which initial payment is limited	90.00%
Non-public equity funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Liquidating investments remaining period	9 years
Credit fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investment redemption notice period	90 days
Long/short commodities fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investment redemption notice period	30 days
Minimum | Secured debt fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Liquidating investments remaining period	3 years
Minimum | Long/short equity funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investment redemption notice period	30 days
Maximum | Secured debt fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Liquidating investments remaining period	8 years
Maximum | Long/short equity funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investment redemption notice period	90 days
Maximum | Long/short commodities fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Payment period for redemption of LP valued at NAV	30 days

Fair Value Measurement (Methodo

Fair Value Measurement (Methodologies Other Than Fair Value) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financial assets:
BOLI	$ 62,562	$ 62,113
Other investments	35,944	110,847
Other assets	115,596	101,428
Financial liabilities:
Other liabilities	207,866	437,600
Not Measured At Fair Value | Carrying Value
Financial assets:
BOLI	62,562	62,113
Other investments	2,902	58,546
Other assets	49,549	34,020
Financial liabilities:
Other liabilities	21,525	21,154
Not Measured At Fair Value | Carrying Value | Senior Notes
Financial liabilities:
Debt	250,000	250,000
Not Measured At Fair Value | Carrying Value | Mortgage Loans
Financial liabilities:
Debt	40,111	40,460
Not Measured At Fair Value | Carrying Value | Line of Credit
Financial liabilities:
Debt	83,000	123,000
Not Measured At Fair Value | Level 3 | Fair Value
Financial assets:
BOLI	62,562	62,113
Other investments	2,902	69,095
Other assets	48,816	33,742
Financial liabilities:
Other liabilities	21,525	21,154
Not Measured At Fair Value | Level 3 | Fair Value | Senior Notes
Financial liabilities:
Debt	269,418	273,153
Not Measured At Fair Value | Level 3 | Fair Value | Mortgage Loans
Financial liabilities:
Debt	40,111	40,460
Not Measured At Fair Value | Level 3 | Fair Value | Line of Credit
Financial liabilities:
Debt	$ 83,000	$ 123,000

Investments (Available-For-Sale

Investments (Available-For-Sale Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Fixed maturities, available for sale
Amortized Cost	$ 2,165,384	$ 2,257,188
Gross Unrealized Gains	15,624	32,610
Gross Unrealized Losses	27,325	9,556
Estimated Fair Value	2,153,683	2,280,242
U.S. Treasury obligations
Fixed maturities, available for sale
Amortized Cost	131,655	134,323
Gross Unrealized Gains	305	485
Gross Unrealized Losses	2,209	1,181
Estimated Fair Value	129,751	133,627
U.S. Government-sponsored enterprise obligations
Fixed maturities, available for sale
Amortized Cost	30,377	21,089
Gross Unrealized Gains	27	73
Gross Unrealized Losses	445	206
Estimated Fair Value	29,959	20,956
State and municipal bonds
Fixed maturities, available for sale
Amortized Cost	324,336	618,414
Gross Unrealized Gains	6,613	14,248
Gross Unrealized Losses	954	419
Estimated Fair Value	329,995	632,243
Corporate debt
Fixed maturities, available for sale
Amortized Cost	1,259,132	1,157,660
Gross Unrealized Gains	7,008	15,205
Gross Unrealized Losses	17,877	5,707
Estimated Fair Value	1,248,263	1,167,158
Residential mortgage-backed securities
Fixed maturities, available for sale
Amortized Cost	217,891	196,741
Gross Unrealized Gains	1,502	2,438
Gross Unrealized Losses	3,973	1,335
Estimated Fair Value	215,420	197,844
Agency commercial mortgage-backed securities
Fixed maturities, available for sale
Amortized Cost	15,078	10,827
Gross Unrealized Gains	29	23
Gross Unrealized Losses	220	108
Estimated Fair Value	14,887	10,742
Other commercial mortgage-backed securities
Fixed maturities, available for sale
Amortized Cost	29,409	16,004
Gross Unrealized Gains	100	91
Gross Unrealized Losses	314	134
Estimated Fair Value	29,195	15,961
Other asset-backed securities
Fixed maturities, available for sale
Amortized Cost	157,506	102,130
Gross Unrealized Gains	40	47
Gross Unrealized Losses	1,333	466
Estimated Fair Value	$ 156,213	$ 101,711

Investments (Available For Sale

Investments (Available For Sale Securities by Contractual Maturity) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Fixed maturities, available for sale
Amortized Cost	$ 2,165,384	$ 2,257,188
Estimated Fair Value	2,153,683	2,280,242
U.S. Treasury obligations
Fixed maturities, available for sale
Amortized Cost	131,655	134,323
Due in one year or less	31,700
Due after one year through five years	73,858
Due after five years through ten years	21,321
Due after ten years	2,872
Estimated Fair Value	129,751	133,627
U.S. Government-sponsored enterprise obligations
Fixed maturities, available for sale
Amortized Cost	30,377	21,089
Due in one year or less	0
Due after one year through five years	8,009
Due after five years through ten years	21,814
Due after ten years	136
Estimated Fair Value	29,959	20,956
State and municipal bonds
Fixed maturities, available for sale
Amortized Cost	324,336	618,414
Due in one year or less	29,481
Due after one year through five years	111,512
Due after five years through ten years	140,004
Due after ten years	48,998
Estimated Fair Value	329,995	632,243
Corporate debt
Fixed maturities, available for sale
Amortized Cost	1,259,132	1,157,660
Due in one year or less	115,385
Due after one year through five years	682,646
Due after five years through ten years	404,159
Due after ten years	46,073
Estimated Fair Value	1,248,263	1,167,158
Residential mortgage-backed securities
Fixed maturities, available for sale
Amortized Cost	217,891	196,741
Estimated Fair Value	215,420	197,844
Agency commercial mortgage-backed securities
Fixed maturities, available for sale
Amortized Cost	15,078	10,827
Estimated Fair Value	14,887	10,742
Other commercial mortgage-backed securities
Fixed maturities, available for sale
Amortized Cost	29,409	16,004
Estimated Fair Value	29,195	15,961
Other asset-backed securities
Fixed maturities, available for sale
Amortized Cost	157,506	102,130
Estimated Fair Value	$ 156,213	$ 101,711

Investments (Narrative) (Detail

Investments (Narrative) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)SecurityBusinessinvestment_interestIssuer	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)SecurityIssuer	Dec. 31, 2016USD ($)
Schedule of Available-for-sale Securities [Line Items]
Number of investment affiliates exceeding shareholder's equity ten percent threshold limit | investment_interest	0
Threshold limit of investments based on shareholders' equity (percent)	10.00%
Securities on deposit with state insurance departments	$ 45,800
Business owned life insurance cost	33,000
Fair Value	$ 297,309		$ 230,889
Number of LPs / LLCs with investment ownership percent over 25% | Business	3
Investment in unconsolidated subsidiaries	$ 401,030		330,591
Equity in earnings, losses from affordable housing projects	(4,100)	$ (3,300)
Affordable housing tax credits	4,600	4,600
Losses from historic tax credit investments	(1,900)	(400)
Tax credits recognized related to historic tax credit investments	700	1,800
Net impairment losses recognized in earnings	0	171
Portion of noncredit OTTI losses recognized in OCI	0	248
Credit-related other-than-temporary impairment recognized in earnings	$ 1,313	$ 1,329	1,313	$ 1,158
Tax Credit Partnerships Almost 100% Ownership
Schedule of Available-for-sale Securities [Line Items]
Number of tax credit partnerships almost 100% ownership percentage | investment_interest	2
Investment in unconsolidated subsidiaries	$ 30,700		32,500
Tax Credit Partnerships Less Than 20% Ownership
Schedule of Available-for-sale Securities [Line Items]
Investment in unconsolidated subsidiaries	49,800		52,100
Other Limited Partnerships and Limited Liability Company, Greater Than 25% Ownership
Schedule of Available-for-sale Securities [Line Items]
Investment in unconsolidated subsidiaries	31,300		30,800
Other Limited Partnerships and Limited Liability Company Less than 25% Ownership
Schedule of Available-for-sale Securities [Line Items]
Investment in unconsolidated subsidiaries	$ 283,500		$ 209,100
Maximum | Tax Credit Partnerships Almost 100% Ownership
Schedule of Available-for-sale Securities [Line Items]
Investment ownership percentage	100.00%
Maximum | Tax Credit Partnerships Less Than 20% Ownership
Schedule of Available-for-sale Securities [Line Items]
Investment ownership percentage	20.00%
Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Required FAL Deposit	$ 123,500
Short-term investments
Schedule of Available-for-sale Securities [Line Items]
Required FAL Deposit	$ 400
Non Government-Backed
Schedule of Available-for-sale Securities [Line Items]
Number of debt securities in unrealized loss position | Security	943		629
Debt securities in unrealized loss position as percentage of total debt securities held	44.90%		26.50%
Number of issuers in unrealized loss position | Issuer	494		375
Single greatest unrealized loss position	$ 500		$ 400
Second greatest unrealized loss position	400		$ 300
Revolving Credit Agreement
Schedule of Available-for-sale Securities [Line Items]
Securities pledged as collateral	$ 120,100

Investments (Investments Held i

Investments (Investments Held in a Loss Position) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Fair Value
Fair Value	$ 1,385,692	$ 850,838
Less than 12 months, Fair Value	1,159,903	603,468
More than 12 months, Fair Value	225,789	247,370
Unrealized Loss
Unrealized Loss	27,325	9,556
Less than 12 months, Unrealized Loss	19,049	4,314
More than 12 months, Unrealized Loss	8,276	5,242
U.S. Treasury obligations
Fair Value
Fair Value	121,718	110,788
Less than 12 months, Fair Value	87,740	67,135
More than 12 months, Fair Value	33,978	43,653
Unrealized Loss
Unrealized Loss	2,209	1,181
Less than 12 months, Unrealized Loss	1,438	554
More than 12 months, Unrealized Loss	771	627
U.S. Government-sponsored enterprise obligations
Fair Value
Fair Value	29,018	17,032
Less than 12 months, Fair Value	22,252	10,182
More than 12 months, Fair Value	6,766	6,850
Unrealized Loss
Unrealized Loss	445	206
Less than 12 months, Unrealized Loss	218	64
More than 12 months, Unrealized Loss	227	142
State and municipal bonds
Fair Value
Fair Value	63,690	23,122
Less than 12 months, Fair Value	55,761	15,168
More than 12 months, Fair Value	7,929	7,954
Unrealized Loss
Unrealized Loss	954	419
Less than 12 months, Unrealized Loss	620	102
More than 12 months, Unrealized Loss	334	317
Corporate debt
Fair Value
Fair Value	848,499	487,578
Less than 12 months, Fair Value	733,344	365,541
More than 12 months, Fair Value	115,155	122,037
Unrealized Loss
Unrealized Loss	17,877	5,707
Less than 12 months, Unrealized Loss	13,216	2,730
More than 12 months, Unrealized Loss	4,661	2,977
Residential mortgage-backed securities
Fair Value
Fair Value	175,295	109,659
Less than 12 months, Fair Value	132,075	64,121
More than 12 months, Fair Value	43,220	45,538
Unrealized Loss
Unrealized Loss	3,973	1,335
Less than 12 months, Unrealized Loss	2,066	402
More than 12 months, Unrealized Loss	1,907	933
Agency commercial mortgage-backed securities
Fair Value
Fair Value	9,547	4,423
Less than 12 months, Fair Value	7,638	2,458
More than 12 months, Fair Value	1,909	1,965
Unrealized Loss
Unrealized Loss	220	108
Less than 12 months, Unrealized Loss	101	34
More than 12 months, Unrealized Loss	119	74
Other commercial mortgage-backed securities
Fair Value
Fair Value	19,145	12,878
Less than 12 months, Fair Value	15,723	7,939
More than 12 months, Fair Value	3,422	4,939
Unrealized Loss
Unrealized Loss	314	134
Less than 12 months, Unrealized Loss	256	82
More than 12 months, Unrealized Loss	58	52
Other asset-backed securities
Fair Value
Fair Value	118,780	85,358
Less than 12 months, Fair Value	105,370	70,924
More than 12 months, Fair Value	13,410	14,434
Unrealized Loss
Unrealized Loss	1,333	466
Less than 12 months, Unrealized Loss	1,134	346
More than 12 months, Unrealized Loss	$ 199	$ 120

Investments (Sales and Purchase

Investments (Sales and Purchases of Available-for-Sale Securities) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Information regarding sales and purchases of available-for-sale securities
Proceeds from sales (exclusive of maturities and paydowns)	$ 379,200	$ 79,200
Purchases	$ 367,872	$ 160,364

Investments (Net Investment Inc

Investments (Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Net Investment Income
Investment fees and expenses	$ (1,677)	$ (1,835)
Net investment income	22,027	23,186
Fixed maturities
Net Investment Income
Investment Income	17,080	20,121
Equities
Net Investment Income
Investment Income	4,867	3,644
Short-term investments, including Other
Net Investment Income
Investment Income	1,308	801
BOLI
Net Investment Income
Investment Income	$ 449	$ 455

Investments (Unconsolidated Sub

Investments (Unconsolidated Subsidiaries) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Unconsolidated Subsidiaries
Investment in unconsolidated subsidiaries	$ 401,030	$ 330,591
Qualified affordable housing project tax credit partnerships
Unconsolidated Subsidiaries
Investment in unconsolidated subsidiaries	80,507	84,607
Other tax credit partnerships
Unconsolidated Subsidiaries
Investment in unconsolidated subsidiaries	5,735	6,118
All other investments, primarily investment fund LPs/LLCs
Unconsolidated Subsidiaries
Investment in unconsolidated subsidiaries	$ 314,788	$ 239,866

Investments (Net Realized Inves

Investments (Net Realized Investment Gains (Losses)) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Investments, Debt and Equity Securities [Abstract]
OTTI losses	$ 0	$ (419,000)
Portion of OTTI losses recognized in other comprehensive income before taxes	0	248,000
Net impairment losses recognized in earnings	0	(171,000)
Gross realized gains, available-for-sale fixed maturities	4,464,000	1,853,000
Gross realized (losses), available-for-sale fixed maturities	(2,047,000)	(67,000)
Net realized gains (losses), equity investments	9,219,000	6,562,000
Net realized gains (losses), other investments	688,000	1,172,000
Change in unrealized holding gains (losses), trading fixed maturities	(49,000)	0
Change in unrealized holding gains (losses), equity investments	(23,845,000)	3,616,000
Change in unrealized holding gains (losses), convertible securities, carried at fair value	(954,000)	313,000
Other	7,000	2,000
Total net realized investment gains (losses)	$ (12,517,000)	$ 13,280,000

Investments (Credit Losses Reco

Investments (Credit Losses Recorded in Earnings) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Other than Temporary Impairment, Credit Losses Recognized in Earnings:
Balance beginning of period	$ 1,313	$ 1,158
Additional credit losses recognized during the period, related to securities for which:
No OTTI has been previously recognized	0	171
Accumulated credit losses related to impaired debt securities, Ending Balance	$ 1,313	$ 1,329

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income taxes liabilities	$ 6.3	$ 8
Unrecognized tax benefits	5.2	5.8
Accrued liability for interest related to unrecognized tax benefits	$ 0.6	$ 0.5

Reserve for Losses and Loss A48

Reserve for Losses and Loss Adjustment Expenses (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018USD ($)partition	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease) [Abstract]
Minimum period for claims resolution (years)	5 years
Number of business partitions | partition	200
Summary of reserve for losses and loss adjustment expenses
Balance, beginning of year	$ 2,048,381	$ 1,993,428	$ 1,993,428
Less reinsurance recoverables on unpaid losses and loss adjustment expenses	335,585	273,475	273,475
Net balance, beginning of year	1,712,796	1,719,953	1,719,953
Net losses:
Current year	152,572	147,927	603,518
Favorable development of reserves established in prior years, net	(22,786)	(28,776)	(134,360)
Total	129,786	119,151	469,158
Paid related to:
Current year	(14,243)	(33,085)	(106,633)
Prior years	(101,078)	(80,709)	(369,682)
Total paid	(115,321)	(113,794)	(476,315)
Net balance, end of period	1,727,261	1,725,310	1,712,796
Plus reinsurance recoverables on unpaid losses and loss adjustment expenses	329,540	271,679	335,585
Balance, end of period	$ 2,056,801	$ 1,996,989	$ 2,048,381

Commitments and Contingencies (

Commitments and Contingencies (Details) - Lloyd's Syndicate $ in Millions	Mar. 31, 2018USD ($)	Mar. 31, 2018GBP (£)	Feb. 28, 2018GBP (£)	Jan. 31, 2018GBP (£)
Other Commitments [Line Items]
Required FAL Deposit	$ 123.9
Current lending capacity under revolving credit agreement | £			£ 30,000,000	£ 20,000,000
Interest rate on revolving credit agreement	3.80%	3.80%
Unused commitments to extend credit	$ 4.6	£ 3,300,000
Commitment to Provide Capital
Other Commitments [Line Items]
Commitments Total	$ 200

Debt (Details)

Debt (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Gross debt	$ 373,111,000	$ 413,460,000
Less debt issuance costs	1,583,000	1,649,000
Debt less debt issuance costs	371,528,000	411,811,000
Senior Notes | Senior notes due 2023
Debt Instrument [Line Items]
Gross debt	$ 250,000,000	$ 250,000,000
Stated interest rate on debt	5.30%	5.30%
Line of Credit | Revolving Credit Agreement
Debt Instrument [Line Items]
Gross debt	$ 83,000,000	$ 123,000,000
Weighted average interest rate on debt	2.24%	1.91%
Line of credit maximum borrowing capacity	$ 250,000,000	$ 250,000,000
Mortgage Loans
Debt Instrument [Line Items]
Gross debt	$ 40,111,000	$ 40,460,000
Stated interest rate on debt	3.42%	2.86%
Mortgage Loans | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate for debt	1.325%	1.325%

Derivatives - Narrative (Detail

Derivatives - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Mortgage Loans | LIBOR
Derivative [Line Items]
Basis spread on variable rate for debt	1.325%	1.325%
Interest Rate Cap
Derivative [Line Items]
Premium paid on derivative for right to receive cash payments	$ 2,000
Floor interest rate on derivative	2.35%
Cap interest rate on derivative	3.675%
Interest Rate Cap | Other assets
Derivative [Line Items]
Derivative asset, notional amount	$ 35,000	$ 35,000

Derivatives - Volume and Fair V

Derivatives - Volume and Fair Value (Details) - Interest Rate Cap - Other assets $ in Thousands	Mar. 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	$ 2,306	$ 1,731

Derivatives - Pre-tax Impact of

Derivatives - Pre-tax Impact of Change in Fair Value (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Interest Rate Cap | Interest expense
Derivative [Line Items]
Gains (Losses) Recognized in Income on Derivatives	$ 575	$ 0

Shareholders' Equity (Narrative

Shareholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended		12 Months Ended
	Feb. 28, 2018	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2015	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorized common stock (in shares)		100,000,000			100,000,000
Authorized preferred stock (in shares)		50,000,000			50,000,000
Quarterly dividend declared, per share (USD per share)		$ 0.310	$ 0.31
Dividend declared		$ 16.6	$ 16.5
Total authorizations which remain available for use		$ 109.6
Common shares acquired (in shares)		0	0
Bonus compensation shares issued (in shares)	2,500
Non-credit loss, net of tax		$ 0.6			$ 0.5
Statutory income tax rate		35.00%	35.00%
Restricted Share Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards in period (in shares)	85,800
Fair value of each unit awarded (USD per share)	$ 44.73
Award vesting period		3 years
Shares issued in period for share-based compensation (in shares)	52,800
Performance Share Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards in period (in shares)	27,200
Shares issued in period for share-based compensation (in shares)	80,600
Performance Share Units | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award payout rate		50.00%
Performance Share Units | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award payout rate		200.00%
Performance Shares Granted in 2015 | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award payout rate				125.00%
Accumulated Other Comprehensive Income (Loss)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reclassification from AOCI to retained earnings for stranded tax effects		$ 3.4
Retained Earnings
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reclassification from AOCI to retained earnings for stranded tax effects		$ (3.4)

Shareholders' Equity (Share-bas

Shareholders' Equity (Share-based Compensation Expense and Related Tax Benefits) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Equity [Abstract]
Share-based compensation expense	$ 902	$ 3,346
Related tax benefits	$ 190	$ 1,171

Shareholders' Equity (AOCI Recl

Shareholders' Equity (AOCI Reclassification) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Reclassifications from AOCI to net income:
Realized investment gains (losses)	$ 2,417	$ 1,616
Tax effect	(508)	(566)
Net reclassification adjustments	1,909	1,050
Deferred tax expense (benefit) included in OCI	$ (7,060)	$ 1,481
Tax rate used to compute the tax effect of amounts reclassified out of OCI	35.00%	35.00%

Variable Interest Entities (Det

Variable Interest Entities (Details) $ in Millions	Mar. 31, 2018USD ($)
Variable Interest Entity, Not Primary Beneficiary | Investment in unconsolidated subsidiaries
Variable Interest Entity [Line Items]
VIE interests carrying value	$ 316.3

Earnings Per Share (Details)

Earnings Per Share (Details) - $ / shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Weighted average number of common shares outstanding, basic (in shares)	53,515,000	53,315,000
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average number of common shares outstanding, diluted (in shares)	53,682,000	53,535,000
Effect of dilutive shares on earnings per share (usd per share)	$ 0	$ (0.01)
Antidilutive shares excluded from computation of earnings per share (in shares)	0	0
Restricted Share Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dilutive securities (in shares)	82,000	78,000
Performance Share Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dilutive securities (in shares)	66,000	121,000
Purchase Match Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dilutive securities (in shares)	19,000	21,000

Segment Information (Narrative)

Segment Information (Narrative) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)segment	Mar. 31, 2017USD ($)	Jan. 01, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Number of operating segments | segment	4
Segregated portfolio cells dividend expense (income)	$ 1,747	$ 2,375
Income tax benefit (expense)	$ 3,422	1,224
Workers' Compensation
Segment Reporting Information [Line Items]
Worker's compensation SPC percentage ceded	100.00%
Lloyd's Syndicate
Segment Reporting Information [Line Items]
Proportion of Capital Provided to support Lloyd's Syndicate 1729			62.00%	58.00%
Specialty Property and Casualty [Member]
Segment Reporting Information [Line Items]
Premiums ceded under quota share agreement	$ 1,900	3,500
Operating Segments | Workers' Compensation
Segment Reporting Information [Line Items]
Segregated portfolio cells dividend expense (income)	1,894	1,174
Income tax benefit (expense)	0	0
Operating Segments | Lloyd's Syndicate
Segment Reporting Information [Line Items]
Segregated portfolio cells dividend expense (income)	0	0
Income tax benefit (expense)	(6)	7
Operating Segments | Specialty Property and Casualty [Member]
Segment Reporting Information [Line Items]
Segregated portfolio cells dividend expense (income)	(30)	(28)
Income tax benefit (expense)	0	0
Operating Segments | Corporate
Segment Reporting Information [Line Items]
Segregated portfolio cells dividend expense (income)	(117)	1,229
Income tax benefit (expense)	$ 3,428	$ 1,217

Segment Information (Financial

Segment Information (Financial Data by Segment) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Net premiums earned	$ 187,159	$ 182,903
Net investment income	22,027	23,186
Equity in earnings (loss) of unconsolidated subsidiaries	1,640	1,808
Net realized gains (losses)	(12,517)	13,280
Other income (expense)	2,723	1,821
Net losses and loss adjustment expenses	(129,786)	(119,151)
Underwriting, policy acquisition and operating expenses	(57,360)	(57,108)
Segregated portfolio cells dividend (expense) income	(1,747)	(2,375)
Interest expense	(3,705)	(4,133)
Income tax benefit (expense)	3,422	1,224
Segment operating results	11,856	41,455
Depreciation and amortization, net of accretion	6,079	7,803
Specialty P&C
Segment Reporting Information [Line Items]
Net premiums earned	116,276	113,058
Workers' Compensation
Segment Reporting Information [Line Items]
Net premiums earned	58,407	55,283
Lloyd's Syndicate
Segment Reporting Information [Line Items]
Net premiums earned	12,476	14,562
Operating Segments | Specialty P&C
Segment Reporting Information [Line Items]
Net premiums earned	116,276	113,058
Net investment income	0	0
Equity in earnings (loss) of unconsolidated subsidiaries	0	0
Net realized gains (losses)	0	0
Other income (expense)	1,256	1,198
Net losses and loss adjustment expenses	(84,585)	(74,994)
Underwriting, policy acquisition and operating expenses	(28,276)	(25,977)
Segregated portfolio cells dividend (expense) income	30	28
Interest expense	0	0
Income tax benefit (expense)	0	0
Segment operating results	4,701	13,313
Depreciation and amortization, net of accretion	1,867	1,911
Operating Segments | Workers' Compensation
Segment Reporting Information [Line Items]
Net premiums earned	58,407	55,283
Net investment income	0	0
Equity in earnings (loss) of unconsolidated subsidiaries	0	0
Net realized gains (losses)	0	0
Other income (expense)	366	145
Net losses and loss adjustment expenses	(36,715)	(34,650)
Underwriting, policy acquisition and operating expenses	(17,333)	(16,691)
Segregated portfolio cells dividend (expense) income	(1,894)	(1,174)
Interest expense	0	0
Income tax benefit (expense)	0	0
Segment operating results	2,831	2,913
Depreciation and amortization, net of accretion	956	837
Operating Segments | Lloyd's Syndicate
Segment Reporting Information [Line Items]
Net premiums earned	12,476	14,562
Net investment income	751	372
Equity in earnings (loss) of unconsolidated subsidiaries	0	0
Net realized gains (losses)	(54)	27
Other income (expense)	331	391
Net losses and loss adjustment expenses	(8,486)	(9,507)
Underwriting, policy acquisition and operating expenses	(7,246)	(6,211)
Segregated portfolio cells dividend (expense) income	0	0
Interest expense	0	0
Income tax benefit (expense)	(6)	7
Segment operating results	(2,234)	(359)
Depreciation and amortization, net of accretion	(1)	(3)
Operating Segments | Corporate
Segment Reporting Information [Line Items]
Net premiums earned	0	0
Net investment income	21,276	22,814
Equity in earnings (loss) of unconsolidated subsidiaries	1,640	1,808
Net realized gains (losses)	(12,463)	13,253
Other income (expense)	943	173
Net losses and loss adjustment expenses	0	0
Underwriting, policy acquisition and operating expenses	(4,678)	(8,315)
Segregated portfolio cells dividend (expense) income	117	(1,229)
Interest expense	(3,705)	(4,133)
Income tax benefit (expense)	3,428	1,217
Segment operating results	6,558	25,588
Depreciation and amortization, net of accretion	3,257	5,058
Inter-segment Eliminations
Segment Reporting Information [Line Items]
Net premiums earned	0	0
Net investment income	0	0
Equity in earnings (loss) of unconsolidated subsidiaries	0	0
Net realized gains (losses)	0	0
Other income (expense)	(173)	(86)
Net losses and loss adjustment expenses	0	0
Underwriting, policy acquisition and operating expenses	173	86
Segregated portfolio cells dividend (expense) income	0	0
Interest expense	0	0
Income tax benefit (expense)	0	0
Segment operating results	0	0
Depreciation and amortization, net of accretion	$ 0	$ 0

Segment Information (Gross Prem

Segment Information (Gross Premiums Earned by Product and Reconciliation to Net Premiums) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Net premiums earned	$ 187,159	$ 182,903
Specialty P&C
Segment Reporting Information [Line Items]
Ceded premiums earned	(17,422)	(18,724)
Net premiums earned	116,276	113,058
Specialty P&C | Healthcare professional liability
Segment Reporting Information [Line Items]
Gross premiums earned	118,685	117,051
Specialty P&C | Legal professional liability
Segment Reporting Information [Line Items]
Gross premiums earned	6,391	6,317
Specialty P&C | Medical technology liability
Segment Reporting Information [Line Items]
Gross premiums earned	8,512	8,312
Specialty P&C | Other
Segment Reporting Information [Line Items]
Gross premiums earned	110	102
Workers' Compensation
Segment Reporting Information [Line Items]
Ceded premiums earned	(7,004)	(5,931)
Net premiums earned	58,407	55,283
Workers' Compensation | Traditional business
Segment Reporting Information [Line Items]
Gross premiums earned	46,030	41,768
Workers' Compensation | Alternative market business
Segment Reporting Information [Line Items]
Gross premiums earned	19,381	19,446
Lloyd's Syndicate
Segment Reporting Information [Line Items]
Ceded premiums earned	(5,491)	(2,623)
Net premiums earned	12,476	14,562
Lloyd's Syndicate | Property and casualty
Segment Reporting Information [Line Items]
Gross premiums earned	$ 17,967	$ 17,185