James River (JRVR) 10-Q 4 May 18 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2018	May 01, 2018
Document And Entity Information [Abstract]
Entity Registrant Name	James River Group Holdings, Ltd.
Entity Central Index Key	1,620,459
Trading Symbol	jrvr
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		29,866,705
Document Type	10-Q
Document Period End Date	Mar. 31, 2018
Amendment Flag	false
Document Fiscal Period Focus	Q1
Document Fiscal Year Focus	2,018

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Fixed maturity securities:
Available-for-sale, at fair value (amortized cost: 2018 – $1,054,902; 2017 – $1,008,662)	$ 1,043,251	$ 1,016,098
Trading, at fair value (amortized cost: 2018 – $3,800; 2017 – $3,801)	3,805	3,808
Equity securities available-for-sale, at fair value (cost: 2018 – $80,464; 2017 – $75,318)	85,957	82,522
Bank loan participations held-for-investment, at amortized cost, net of allowance	257,426	238,214
Short-term investments	26,235	36,804
Other invested assets	74,974	70,208
Total invested assets	1,491,648	1,447,654
Cash and cash equivalents	151,046	163,495
Accrued investment income	8,713	8,381
Premiums receivable and agents’ balances, net	391,456	352,436
Reinsurance recoverable on unpaid losses	331,245	302,524
Reinsurance recoverable on paid losses	16,501	11,292
Prepaid reinsurance premiums	96,141	91,979
Deferred policy acquisition costs	70,769	72,365
Intangible assets, net	38,185	38,334
Goodwill	181,831	181,831
Other assets	84,475	86,404
Total assets	2,862,010	2,756,695
Liabilities:
Reserve for losses and loss adjustment expenses	1,369,548	1,292,349
Unearned premiums	432,248	418,114
Payables to reinsurers	59,138	56,268
Senior debt	98,300	98,300
Junior subordinated debt	104,055	104,055
Accrued expenses	35,138	39,295
Other liabilities	77,813	53,615
Total liabilities	2,176,240	2,061,996
Commitments and contingent liabilities
Shareholders’ equity:
Common Shares – 2018 and 2017: $0.0002 par value; 200,000,000 shares authorized; 29,866,705 and 29,696,682 shares issued and outstanding, respectively	6	6
Preferred Shares – 2018 and 2017: $0.00125 par value; 20,000,000 shares authorized; no shares issued and outstanding	0	0
Additional paid-in capital	639,183	636,149
Retained earnings	58,753	48,198
Accumulated other comprehensive (loss) income	(12,172)	10,346
Total shareholders’ equity	685,770	694,699
Total liabilities and shareholders’ equity	$ 2,862,010	$ 2,756,695

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Available-for-sale debt securities, amortized cost	$ 1,054,902	$ 1,008,662
Trading securities, debt, amortized cost	3,800	3,801
Available-for-sale equity securities, amortized cost	$ 80,464	$ 75,318
Common stock, par value (in dollars per share)	$ 0.0002	$ 0.0002
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	29,866,705	29,696,682
Common stock, shares outstanding	29,866,705	29,696,682
Preferred stock par value (in dollars per share)	$ 0.00125	$ 0.00125
Preferred stock, shares authorized	20,000,000	20,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0

Condensed Consolidated Statemen

Condensed Consolidated Statements of Income and Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues
Gross written premiums	$ 298,116	$ 224,179
Ceded written premiums	(87,138)	(66,269)
Net written premiums	210,978	157,910
Change in net unearned premiums	(10,036)	(3,223)
Net earned premiums	200,942	154,687
Net investment income	13,256	16,733
Net realized and unrealized (losses) gains on investments	(810)	1,047
Other income	4,956	3,935
Total revenues	218,344	176,402
Expenses
Losses and loss adjustment expenses	143,772	105,369
Other operating expenses	54,783	48,893
Other expenses	4	(114)
Interest expense	2,522	2,123
Amortization of intangible assets	149	149
Total expenses	201,230	156,420
Income before taxes	17,114	19,982
Income tax expense	1,481	1,532
Net income	15,633	18,450
Other comprehensive (loss) income:
Net unrealized (losses) gains, net of taxes of $(544) in 2018 and $1,514 in 2017	(18,547)	4,034
Total comprehensive (loss) income	$ (2,914)	$ 22,484
Per share data:
Basic earnings per share (in dollars per share)	$ 0.53	$ 0.63
Diluted earnings per share (in dollars per share)	0.52	0.61
Dividend declared per share (in dollars per share)	$ 0.30	$ 0.30
Weighted-average common shares outstanding:
Basic (in shares)	29,764,320	29,289,588
Diluted (in shares)	30,193,303	30,327,423

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Income and Comprehensive Income (Unaudited) (Parentheticals) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Tax on net unrealized gains (losses)	$ (544)	$ 1,514

Condensed Consolidated Stateme6

Condensed Consolidated Statements of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Shares	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income
Balance (in shares) at Dec. 31, 2016		29,257,566
Balance at Dec. 31, 2016	$ 693,221	$ 6	$ 636,856	$ 55,232	$ 1,127
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	18,450			18,450
Other comprehensive income	4,034				4,034
Dividends	(8,810)			(8,810)
Exercised (in shares)		63,467
Exercise of stock options	198		198
Vesting of RSUs (in shares)		23,294
Vesting of RSUs	(627)		(627)
Compensation expense under share incentive plans	1,794		1,794
Balance (in shares) at Mar. 31, 2017		29,344,327
Balance at Mar. 31, 2017	$ 708,260	$ 6	638,221	64,872	5,161
Balance (in shares) at Dec. 31, 2017	29,696,682	29,696,682
Balance at Dec. 31, 2017	$ 694,699	$ 6	636,149	48,198	10,346
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	15,633			15,633
Net income | ASU 2016-01				(1,400)
Other comprehensive income	(18,547)				(18,547)
Dividends	(9,049)			(9,049)
Exercised (in shares)		127,196
Exercise of stock options	2,355		2,355
Vesting of RSUs (in shares)		42,827
Vesting of RSUs	(776)		(776)
Compensation expense under share incentive plans	$ 1,455		1,455
Balance (in shares) at Mar. 31, 2018	29,866,705	29,866,705
Balance at Mar. 31, 2018	$ 685,770	$ 6	$ 639,183	58,753	(12,172)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of adoption of ASU | ASU 2016-01	0			4,682	(4,682)
Cumulative effect of adoption of ASU | ASU 2018-02	$ 0			$ (711)	$ 711

Condensed Consolidated Stateme7

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating activities
Net cash provided by operating activities	$ 48,461	$ 16,112
Securities available-for-sale:
Purchases – fixed maturity securities	(118,652)	(46,276)
Sales – fixed maturity securities	26,392	32,148
Maturities and calls – fixed maturity securities	45,245	15,406
Purchases – equity securities	(5,949)	0
Sales – equity securities	766	409
Bank loan participations:
Purchases	(66,059)	(75,983)
Sales	35,708	37,462
Maturities	11,427	18,840
Other invested assets:
Purchases	(4,992)	(250)
Short-term investments, net	10,569	(2,517)
Securities receivable or payable, net	12,576	(336)
Purchases of property and equipment	(275)	(970)
Net cash used in investing activities	(53,244)	(22,067)
Financing activities
Dividends paid	(9,074)	(8,885)
Issuance of common shares under equity incentive plans	2,862	303
Common share repurchases	(1,283)	(732)
Repayments of financing obligations net of proceeds	(171)	(291)
Net cash used in financing activities	(7,666)	(9,605)
Change in cash and cash equivalents	(12,449)	(15,560)
Cash and cash equivalents at beginning of period	163,495	109,784
Cash and cash equivalents at end of period	151,046	94,224
Supplemental information
Interest paid	$ 2,509	$ 2,101

Accounting Policies

Accounting Policies	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Accounting Policies	Accounting Policies Organization James River Group Holdings, Ltd. (referred to as “JRG Holdings” or, with its subsidiaries, the “Company”) is an exempted holding company registered in Bermuda, organized for the purpose of acquiring and managing insurance and reinsurance entities. The Company owns six insurance companies based in the United States (“U.S.”) focused on specialty insurance niches and two Bermuda-based reinsurance companies as described below: • James River Group Holdings UK Limited (“James River UK”) is an insurance holding company formed in 2015 in the United Kingdom (“U.K.”). JRG Holdings contributed James River Group, Inc. (“James River Group”), a U.S. insurance holding company, to James River UK in 2015. • James River Group is a Delaware domiciled insurance holding company formed in 2002 which owns all of the Company’s U.S.-based subsidiaries, either directly or indirectly through one of its wholly-owned U.S. subsidiaries. James River Group oversees the Company’s U.S. insurance operations and maintains all of the outstanding debt in the U.S. • James River Insurance Company is an Ohio domiciled excess and surplus lines insurance company that, with its wholly-owned insurance subsidiary, James River Casualty Company, is authorized to write business in every state and the District of Columbia. • Falls Lake National Insurance Company (“Falls Lake National”) is an Ohio domiciled insurance company which wholly owns Stonewood Insurance Company (“Stonewood Insurance”), a North Carolina domiciled company, Falls Lake General Insurance Company, an Ohio domiciled company, and Falls Lake Fire and Casualty Company, a California domiciled company. Falls Lake National began writing specialty admitted fronting and program business in late 2013. Falls Lake Fire and Casualty began operations in 2016. • JRG Reinsurance Company Ltd. (“JRG Re”) was formed in 2007 and commenced operations in 2008. JRG Re, a Bermuda domiciled reinsurer, primarily provides non-catastrophe casualty reinsurance to U.S. third parties. • Carolina Re Ltd (“Carolina Re”) was formed in 2018 and provides reinsurance to the Company’s U.S.-based insurance subsidiaries. Carolina Re has entered into a stop loss reinsurance treaty with JRG Re. Basis of Presentation The accompanying condensed consolidated financial statements and notes have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information and do not contain all of the information and footnotes required by U.S. GAAP for complete financial statements. The condensed consolidated financial statements include the results of the Company and its subsidiaries from their respective dates of inception or acquisition, as applicable. Readers are urged to review the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 for a more complete description of the Company’s business and accounting policies. In the opinion of management, all adjustments necessary for a fair presentation of the condensed consolidated financial statements have been included. Such adjustments consist only of normal recurring items. Interim results are not necessarily indicative of results of operations for the full year. The consolidated balance sheet as of December 31, 2017 was derived from the Company’s audited annual consolidated financial statements. Intercompany transactions and balances have been eliminated. Estimates and Assumptions Preparation of the condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the condensed consolidated financial statements and accompanying disclosures. Those estimates are inherently subject to change, and actual results may ultimately differ from those estimates. Variable Interest Entities Entities that do not have sufficient equity at risk to allow the entity to finance its activities without additional financial support or in which the equity investors, as a group, do not have the characteristic of a controlling financial interest are referred to as variable interest entities (“VIE”). A VIE is consolidated by the variable interest holder that is determined to have the controlling financial interest (primary beneficiary) as a result of having both the power to direct the activities of a VIE that most significantly impact the VIE’s economic performance and the obligation to absorb losses or the right to receive benefits from the VIE that could potentially be significant to the VIE. The Company determines whether it is the primary beneficiary of an entity subject to consolidation based on a qualitative assessment of the VIE’s capital structure, contractual terms, nature of the VIE’s operations and purpose, and the Company’s relative exposure to the related risks of the VIE on the date it becomes initially involved in the VIE. The Company reassesses its VIE determination with respect to an entity on an ongoing basis. The Company holds interests in VIEs through certain equity method investments included in “other invested assets” in the accompanying condensed consolidated balance sheets. The Company has determined that it should not consolidate any of the VIEs as it is not the primary beneficiary in any of the relationships. Although the investments resulted in the Company holding variable interests in the entities, they did not empower the Company to direct the activities that most significantly impact the economic performance of the entities. The Company’s investments related to these VIEs totaled $32.6 million and $32.1 million as of March 31, 2018 and December 31, 2017 , respectively, representing the Company’s maximum exposure to loss. Income Tax Expense Our effective tax rate fluctuates from period to period based on the relative mix of income reported by country and the respective tax rates imposed by each tax jurisdiction. For the three months ended March 31, 2018 and 2017 , our U.S. federal income tax expense was 8.7% and 7.7% of income before taxes, respectively. For U.S.-sourced income, the Company’s U.S. federal income tax expense differs from the amounts computed by applying the federal statutory income tax rate (21% in 2018 and 35% in 2017) to income before taxes due primarily to interest income on tax-advantaged state and municipal securities (state and municipal securities represent 12.4% and 10.9% of our available-for-sale securities at March 31, 2018 and 2017 , respectively), dividends received income, and excess tax benefits on share based compensation. Financial results reflect provisional amounts related to the December 2017 enactment of the Tax Cuts and Jobs Act of 2017 ( “ TCJA ” ). These provisional estimates are based on the Company’s initial analysis and current interpretation of the legislation. Given the complexity of the legislation, anticipated guidance from the U.S. Treasury, and the potential for additional guidance from the SEC or the Financial Accounting Standards Board ( “FASB”) , these estimates may be adjusted during 2018. Adopted Accounting Standards Effective January 1, 2018, the Company adopted Accounting Standards Update (“ASU”) 2014-09, Revenue from Contracts with Customers (Topic 606) . The guidance applies to all companies that either enter into contracts with customers to transfer goods or services or enter into contracts for the transfer of nonfinancial assets, unless those contracts are within the scope of other standards, such as insurance contracts. Under this guidance, a company will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. Judgments required in adopting this update may include identifying performance obligations in the contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. The adoption of ASU 2014-09 had no impact on reported fee income and there was no cumulative effect of initially applying the update. Effective January 1, 2018, the Company adopted ASU 2016-01, Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities . Among other things, this ASU 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. Upon adoption on January 1, 2018, the Company made a $4.7 million cumulative-effect adjustment to increase retained earnings and reduce accumulated other comprehensive income. The adoption of ASU 2016-01 did not materially impact the Company's financial position, cash flows, or total comprehensive income. The Company's results of operations were impacted as changes in fair value of equity instruments are now presented in net income rather than other comprehensive (loss) income. For the three months ended March 31, 2018, the impact was a $1.4 million reduction in net income and a $0.05 reduction in basic and diluted earnings per share. Effective January 1, 2018, the Company adopted ASU 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. This update was issued as a result of the enactment of the TCJA on December 22, 2017. The ASU allows for the option to reclassify the stranded tax effects resulting from the implementation of the TCJA out of accumulated other comprehensive income and into retained earnings. As the adoption of ASU 2016-01 in 2018 resulted in the reclassification of the entire unrealized balance on equity securities from accumulated other comprehensive income into retained earnings, only the stranded tax effects on the unrealized balances of fixed income securities were impacted by the adoption of ASU 2018-02. The reclassification resulted in a $711,000 decrease to the Company's retained earnings with a corresponding increase to accumulated other comprehensive income in the first quarter of 2018. Prospective Accounting Standards In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) . Under current guidance for lessees, leases are only included on the balance sheet if certain criteria, classifying the agreement as a capital lease, are met. This update will require the recognition of a right-of-use asset and a corresponding lease liability, discounted to the present value, for all leases that extend beyond 12 months. This ASU is effective for annual and interim reporting periods beginning after December 15, 2018. Upon adoption, leases will be recognized and measured at the beginning of the earliest period presented using a modified retrospective approach. The Company is currently evaluating ASU 2016-02 to determine the potential impact that adopting this standard will have on its financial statements. In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. Current GAAP delays the recognition of credit losses until it is probable a loss has been incurred. The update will require financial assets measured at amortized cost, such as bank loan participations held for investment, to be presented at the net amount expected to be collected by means of an allowance for credit losses that runs through net income. Credit losses relating to available-for-sale debt securities will also be recorded through an allowance for credit losses, with the amount of the allowance limited to the amount by which fair value is below amortized cost. This ASU is effective for annual and interim reporting periods beginning after December 15, 2019. Upon adoption, this ASU will be applied using the modified-retrospective approach, by which a cumulative-effect adjustment will be made to retained earnings as of the beginning of the first reporting period presented. The Company has not yet completed the analysis of how adopting this ASU will affect the Company’s financial statements.

Investments

Investments	3 Months Ended
	Mar. 31, 2018
Investments [Abstract]
Investments	Investments The Company’s available-for-sale investments are summarized as follows: Cost or Gross Gross Fair (in thousands) March 31, 2018 Fixed maturity securities: State and municipal $ 137,478 $ 4,029 $ (1,782 ) $ 139,725 Residential mortgage-backed 186,279 509 (5,690 ) 181,098 Corporate 445,058 3,054 (8,486 ) 439,626 Commercial mortgage and asset-backed 192,941 173 (2,310 ) 190,804 Obligations of U.S. government corporations and agencies 7,804 — (29 ) 7,775 U.S. Treasury securities and obligations guaranteed by the U.S. government 83,317 73 (1,171 ) 82,219 Redeemable preferred stock 2,025 — (21 ) 2,004 Total fixed maturity securities 1,054,902 7,838 (19,489 ) 1,043,251 Equity securities 80,464 6,845 (1,352 ) 85,957 Total investments available-for-sale $ 1,135,366 $ 14,683 $ (20,841 ) $ 1,129,208 December 31, 2017 Fixed maturity securities: State and municipal $ 139,382 $ 5,587 $ (603 ) $ 144,366 Residential mortgage-backed 160,379 723 (2,441 ) 158,661 Corporate 408,857 7,503 (2,639 ) 413,721 Commercial mortgage and asset-backed 182,595 714 (698 ) 182,611 Obligations of U.S. government corporations and agencies 35,948 — (101 ) 35,847 U.S. Treasury securities and obligations guaranteed by the U.S. government 79,476 37 (639 ) 78,874 Redeemable preferred stock 2,025 — (7 ) 2,018 Total fixed maturity securities 1,008,662 14,564 (7,128 ) 1,016,098 Equity securities 75,318 7,830 (626 ) 82,522 Total investments available-for-sale $ 1,083,980 $ 22,394 $ (7,754 ) $ 1,098,620 The amortized cost and fair value of available-for-sale investments in fixed maturity securities at March 31, 2018 are summarized, by contractual maturity, as follows: Cost or Fair (in thousands) One year or less $ 33,850 $ 33,743 After one year through five years 327,069 323,368 After five years through ten years 185,400 181,026 After ten years 127,338 131,208 Residential mortgage-backed 186,279 181,098 Commercial mortgage and asset-backed 192,941 190,804 Redeemable preferred stock 2,025 2,004 Total $ 1,054,902 $ 1,043,251 Actual maturities may differ for some securities because borrowers have the right to call or prepay obligations with or without penalties. The following table shows the Company’s gross unrealized losses and fair value for available-for-sale securities aggregated by investment category and the length of time that individual securities have been in a continuous unrealized loss position: Less Than 12 Months 12 Months or More Total Fair Gross Fair Gross Fair Gross (in thousands) March 31, 2018 Fixed maturity securities: State and municipal $ 61,275 $ (1,325 ) $ 10,454 $ (457 ) $ 71,729 $ (1,782 ) Residential mortgage-backed 90,188 (1,743 ) 79,455 (3,947 ) 169,643 (5,690 ) Corporate 260,523 (5,309 ) 64,506 (3,177 ) 325,029 (8,486 ) Commercial mortgage and asset-backed 94,429 (1,578 ) 22,658 (732 ) 117,087 (2,310 ) Obligations of U.S. government corporations and agencies — — 7,775 (29 ) 7,775 (29 ) U.S. Treasury securities and obligations guaranteed by the U.S. government 53,118 (913 ) 18,080 (258 ) 71,198 (1,171 ) Redeemable preferred stock 2,004 (21 ) — — 2,004 (21 ) Total fixed maturity securities 561,537 (10,889 ) 202,928 (8,600 ) 764,465 (19,489 ) Equity securities 17,816 (811 ) 5,685 (541 ) 23,501 (1,352 ) Total investments available-for-sale $ 579,353 $ (11,700 ) $ 208,613 $ (9,141 ) $ 787,966 $ (20,841 ) December 31, 2017 Fixed maturity securities: State and municipal $ 40,117 $ (318 ) $ 10,662 $ (285 ) $ 50,779 $ (603 ) Residential mortgage-backed 50,447 (261 ) 84,193 (2,180 ) 134,640 (2,441 ) Corporate 113,464 (846 ) 66,954 (1,793 ) 180,418 (2,639 ) Commercial mortgage and asset-backed 53,965 (244 ) 25,299 (454 ) 79,264 (698 ) Obligations of U.S. government corporations and agencies 3,024 (1 ) 32,154 (100 ) 35,178 (101 ) U.S. Treasury securities and obligations guaranteed by the U.S. government 50,760 (430 ) 26,707 (209 ) 77,467 (639 ) Redeemable preferred stock 2,018 (7 ) — — 2,018 (7 ) Total fixed maturity securities 313,795 (2,107 ) 245,969 (5,021 ) 559,764 (7,128 ) Equity securities 5,859 (65 ) 5,665 (561 ) 11,524 (626 ) Total investments available-for-sale $ 319,654 $ (2,172 ) $ 251,634 $ (5,582 ) $ 571,288 $ (7,754 ) The Company held securities of 205 issuers that were in an unrealized loss position at March 31, 2018 with a total fair value of $788.0 million and gross unrealized losses of $20.8 million. None of the fixed maturity securities with unrealized losses has ever missed, or been delinquent on, a scheduled principal or interest payment. At March 31, 2018 , 99.9% of the Company’s fixed maturity security portfolio was rated “BBB-” or better (“investment grade”) by Standard & Poor’s or received an equivalent rating from another nationally recognized rating agency. Fixed maturity securities with ratings below investment grade by Standard & Poor’s or another nationally recognized rating agency at March 31, 2018 had an aggregate fair value of $868,000 and an aggregate net unrealized loss of $26,000 . Management concluded that none of the fixed maturity securities with an unrealized loss at March 31, 2018 or December 31, 2017 experienced an other-than-temporary impairment. Management does not intend to sell available-for-sale securities in an unrealized loss position, and it is not “more likely than not” that the Company will be required to sell these securities before a recovery in their value to their amortized cost basis occurs. A t December 31, 2017 , management concluded that one equity security, based on the severity and duration of the impairment, had experienced an other-than-temporary impairment. Accordingly, the Company recorded an impairment loss of $1.5 million in 2017. Management concluded that none of the other equity securities with an unrealized loss at December 31, 2017 experienced an other-than-temporary impairment. At December 31, 2017 , the Company held a participation in a loan with unpaid principal of $807,000 issued by a company that produces and supplies power to Puerto Rico through a power purchase agreement with Puerto Rico Electric Power Authority (“PREPA”), a public corporation and governmental agency of the Commonwealth of Puerto Rico. Management concluded that an allowance for credit losses should be established on the loan at December 31, 2017 to reduce its carrying value to $0 . In the first quarter of 2018, the full outstanding principal on the loan was repaid and the Company recognized a realized gain of $807,000 on the repayment. The Company’s bank loan portfolio includes loans to oil and gas companies in the energy sector. The market values of these loans were previously impacted by declining energy prices. At March 31, 2018 , the Company’s oil and gas exposure in the bank loan portfolio was in three loans with a carrying value of $4.7 million and an unrealized loss of $143,000 . All of the loans were current at March 31, 2018 . Management concluded that two of these loans were impaired as of March 31, 2018 . At March 31, 2018 , the two impaired loans had a carrying value of $1.7 million , unpaid principal of $2.1 million and an allowance for credit losses of $300,000 . At December 31, 2017 , three loans were impaired with a carrying value of $4.6 million , unpaid principal of $6.9 million and an allowance for credit losses of $2.3 million . Management concluded that one non-energy sector loan was impaired at December 31, 2017 . At December 31, 2017 , the impaired loan had a carrying value of $561,000 , unpaid principal of $706,000 , and an allowance for credit losses of $145,000 . The aggregate allowance for credit losses was $300,000 at March 31, 2018 on impaired loans from two issuers with a total carrying value of $1.7 million and unpaid principal of $2.1 million . At December 31, 2017 , the aggregate allowance for credit losses was $3.2 million on impaired loans from five issuers with a total carrying value of $5.1 million and unpaid principal of $8.4 million . The aggregate allowance for credit losses on impaired loans was $639,000 at March 31, 2017 and $943,000 at December 31, 2016. Bank loan participations generally have a credit rating that is below investment grade (i.e. below “BBB-” for Standard & Poor’s) at the date of purchase. These bank loans are primarily senior, secured floating-rate debt rated “BB”, “B”, or “CCC” by Standard & Poor’s or an equivalent rating from another nationally recognized rating agency. These bank loans include assignments of, and participations in, performing and non-performing senior corporate debt generally acquired through primary bank syndications and in secondary markets. Bank loans consist of, but are not limited to, term loans, the funded and unfunded portions of revolving credit loans, and other similar loans and investments. Management believed that it was probable at the time that these loans were acquired that the Company would be able to collect all contractually required payments receivable. Generally, the accrual of interest on a bank loan participation is discontinued when the contractual payment of principal or interest has become 90 days past due or management has serious doubts about further collectability of principal or interest. A bank loan participation may remain on accrual status if it is in the process of collection and is either guaranteed or well secured. Generally, bank loan participations are restored to accrual status when the obligation is brought current, has performed in accordance with the contractual terms for a reasonable period of time, and the ultimate collectability of the total contractual principal and interest is no longer in doubt. Interest received on nonaccrual loans generally is reported as investment income. There were no bank loans on nonaccrual status at March 31, 2018 or December 31, 2017 . The allowance for credit losses is maintained at a level believed adequate by management to absorb estimated probable credit losses. Management’s periodic evaluation of the adequacy of the allowance is based on consultations and a dvice of the Company’s independent investment manager, known and inherent risks in the portfolio, adverse situations that may affect the borrower’s ability to repay, the estimated value of any underlying collateral, current economic conditions, and other relevant factors. The Company generally records an allowance equal to the difference between the fair value and the amortized cost of bank loans that it has determined to be impaired as a practical expedient for an estimate of probable future cash flows to be collected on those bank loans. Bank loans are charged off against the allowance after all means of collection have been exhausted and the potential for recovery is considered remote. The average recorded investment in impaired bank loans was $3.4 million and $5.3 million during the three months ended March 31, 2018 and 2017 , respectively. Investment income of $20,000 and $84,000 , respectively, was recognized during the time within those periods that the loans were impaired. The Company recorded net realized investment gains of $3,000 and $177,000 in the three months ended March 31, 2018 and 2017 , respectively, for changes in the fair value of impaired bank loans. Changes in unrealized gains or losses on securities held for trading are recorded as trading gains or losses within net investment income. Net investment income for the three months ended March 31, 2018 includes $3,000 of net trading losses, all relating to securities still held at March 31, 2018 . The Company’s realized gains and losses are summarized as follows: Three Months Ended 2018 2017 (in thousands) Fixed maturity securities: Gross realized gains $ 22 $ 338 Gross realized losses (223 ) (296 ) (201 ) 42 Bank loan participations: Gross realized gains 1,220 1,136 Gross realized losses (100 ) (539 ) 1,120 597 Equity securities: Gross realized gains — 409 Gross realized losses (15 ) — Changes in fair values of equity securities (1,710 ) — (1,725 ) 409 Short-term investments and other: Gross realized gains — — Gross realized losses (4 ) (1 ) (4 ) (1 ) Total $ (810 ) $ 1,047 Realized investment gains or losses are determined on a specific identification basis. The Company invests selectively in private debt and equity opportunities. These investments, which together comprise the Company’s other invested assets, are primarily focused in renewable energy, limited partnerships, and bank holding companies. Carrying Value Investment Income March 31, December 31, Three Months Ended 2018 2017 2018 2017 (in thousands) Renewable energy LLCs (a) $ 32,592 $ 32,063 $ 1,211 $ 5,594 Renewable energy notes receivable ( b) 8,750 7,278 297 — Limited partnerships (c) 29,132 26,367 226 382 Bank holding companies (d) 4,500 4,500 86 86 Total other invested assets $ 74,974 $ 70,208 $ 1,820 $ 6,062 (a) The Company’s Corporate and Other segment owns equity interests ranging from 2.6% to 32.8% in various LLCs whose principal objective is capital appreciation and income generation from owning and operating renewable energy production facilities (wind and solar). The LLCs are managed by an affiliate of the Company’s largest shareholder and the Company’s Non-Exucitive Chairman has invested in certain of these LLCs. The equity method is used to account for the Company’s LLC investments. Income for the LLCs primarily reflects adjustments to the carrying values of investments in renewable energy projects to their determined fair values. The fair value adjustments are included in revenues for the LLCs. Expenses for the LLCs are not significant and are comprised of administrative and interest expenses. The Company received cash distributions from these investments totaling $1.2 million and $1.6 million in the three months ended March 31, 2018 and 2017 , respectively. (b) The Company has invested in notes receivable for renewable energy projects. At March 31, 2018 , the Company holds an $8.8 million note issued by an affiliate of the Company’s largest shareholder. Interest on the note, which matures in 2021, is fixed at 15.0% . Interest income on the note was $297,000 for the three months ended March 31, 2018 . (c) The Company owns investments in limited partnerships that invest in concentrated portfolios including publicly-traded small cap equities, loans of middle market private equity sponsored companies, equity tranches of collateralized loan obligations ( “ CLOs ” ), and tranches of distressed home loans. Income f rom the partnerships is recognized under the equity method of accounting. The Company’s Corporate and Other segment held an investment in a limited partnership with a carrying value of $2.9 million at March 31, 2018 . The Company recognized investment losses of $125,000 and investment income of $68,000 on the investment for the three months ended March 31, 2018 and 2017 , respectively. The Company’s Excess and Surplus Lines segment holds investments in limited partnerships of $26.3 million at March 31, 2018 . Investment income of $351,000 and $314,000 was recognized on the investments for the three months ended March 31, 2018 and 2017 , respectively. At March 31, 2018 , the Company’s Excess and Surplus Lines segment has outstanding commitments to invest another $2.6 million in these limited partnerships. (d) The Company holds $4.5 million of subordinated notes issued by a bank holding company. Interest on the notes, which mature on August 12, 2023, is fixed at 7.6% per annum. Interest income on the notes was $86,000 in both three months ended March 31, 2018 and 2017 . The Company’s Chairman was previously the Lead Independent Director of the bank holding company and an investor in the bank holding company. Additionally, one of the Company’s directors was an investor in the bank holding company and is currently a lender to the bank holding company. At March 31, 2018 , the Company held an investment in a CLO where one of the underlying loans was issued by the bank holding company. The investment, with a carrying value of $4.7 million at March 31, 2018 , is classified as an available-for-sale fixed maturity. The Company previously held common shares issued by the bank holding company. Realized investments gains of $409,000 were recognized in the three months ended March 31, 2017 related to the sale of common shares of the bank holding company. The Company holds a $1.0 million certificate of deposit issued by the bank holding company. The certificate of deposit, which matures on December 19, 2018, is carried as a short-term investment. Interest income of $0 and $1,000 was recognized on this investment for the three months ended March 31, 2018 and 2017 , respectively.

Goodwill and Intangible Assets

Goodwill and Intangible Assets	3 Months Ended
	Mar. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	Goodwill and Intangible Assets On December 11, 2007, the Company completed an acquisition of James River Group by acquiring 100% of the outstanding shares of James River Group common stock, referred to herein as the “Merger”. The transaction was accounted for under the purchase method of accounting, and goodwill and intangible assets were recognized by the Company as a result of the transaction. Goodwill resulting from the Merger was $181.8 million at March 31, 2018 and December 31, 2017 . The gross carrying amounts and accumulated amortization for each major specifically identifiable intangible asset class were as follows: March 31, 2018 December 31, 2017 Life Gross Accumulated Gross Accumulated ($ in thousands) Intangible Assets Trademarks Indefinite $ 22,200 $ — $ 22,200 $ — Insurance licenses and authorities Indefinite 9,164 — 9,164 — Identifiable intangibles not subject to amortization 31,364 — 31,364 — Broker relationships 24.6 11,611 4,790 11,611 4,641 Identifiable intangible assets subject to amortization 11,611 4,790 11,611 4,641 $ 42,975 $ 4,790 $ 42,975 $ 4,641

Earnings Per Share

Earnings Per Share	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Earnings Per Share	Earnings Per Share The following represents a reconciliation of the numerator and denominator of the basic and diluted earnings per share computations contained in the condensed consolidated financial statements: Three Months Ended 2018 2017 (in thousands, except share and per share amounts) Net income to shareholders $ 15,633 $ 18,450 Weighted average common shares outstanding: Basic 29,764,320 29,289,588 Common share equivalents 428,983 1,037,835 Diluted 30,193,303 30,327,423 Earnings per share: Basic $ 0.53 $ 0.63 Common share equivalents (0.01 ) (0.02 ) Diluted $ 0.52 $ 0.61 Common share equivalents relate to stock options and restricted share units (“RSU’s”). For the three months ended March 31, 2018 and 2017, common share equivalents of 192,817 and 97,755 shares, respectively, were excluded from the calculations of diluted earnings per share as their effects were anti-dilutive.

Reserve for Losses and Loss Adj

Reserve for Losses and Loss Adjustment Expenses	3 Months Ended
	Mar. 31, 2018
Liability for Claims and Claims Adjustment Expense [Abstract]
Reserve for Losses and Loss Adjustment Expenses	Reserve for Losses and Loss Adjustment Expenses The following table provides a reconciliation of the beginning and ending reserve balances for losses and loss adjustment expenses, net of reinsurance, to the gross amounts reported in the condensed consolidated balance sheets: Three Months Ended 2018 2017 (in thousands) Reserve for losses and loss adjustment expenses net of reinsurance recoverables at beginning of period $ 989,825 $ 761,128 Add: Incurred losses and loss adjustment expenses net of reinsurance: Current year 146,382 108,783 Prior years (2,610 ) (3,414 ) Total incurred losses and loss and adjustment expenses 143,772 105,369 Deduct: Loss and loss adjustment expense payments net of reinsurance: Current year 12,177 3,698 Prior years 83,117 71,018 Total loss and loss adjustment expense payments 95,294 74,716 Reserve for losses and loss adjustment expenses net of reinsurance recoverables at end of period 1,038,303 791,781 Add: Reinsurance recoverables on unpaid losses and loss adjustment expenses at end of period 331,245 188,782 Reserve for losses and loss adjustment expenses gross of reinsurance recoverables on unpaid losses and loss adjustment expenses at end of period $ 1,369,548 $ 980,563 The Company experienced $2.6 million of favorable reserve development in the three months ended March 31, 2018 on the reserve for losses and loss adjustment expenses held at December 31, 2017 . This reserve development included $1.1 million of favorable development in the Excess and Surplus Lines segment, primarily from the 2016 and 2017 accident years. This favorable development occurred because our actuarial studies at March 31, 2018 for the Excess and Surplus Lines segment indicated that our loss experience on our casualty business continues to be below our initial expected loss ratios. The Specialty Admitted Insurance segment experienced $1.3 million of favorable development, primarily due to favorable development in the workers' compensation business for the 2014 through 2016 accident years. The Company also experienced $176,000 of favorable development in the Casualty Reinsurance segment. The Company experienced $3.4 million of favorable reserve development in the three months ended March 31, 2017 on the reserve for losses and loss adjustment expenses held at December 31, 2016 . This reserve development included $3.2 million of favorable development in the Excess and Surplus Lines segment, primarily from the 2016 and 2014 accident years which were partially offset by adverse development in the 2006 accident year. This favorable development occurred because our actuarial studies at March 31, 2017 for the Excess and Surplus Lines segment indicated that our loss experience on our casualty business continues to be below our initial expected loss ratios. In addition, the Specialty Admitted Insurance segment experienced $42,000 of favorable development and the Casualty Reinsurance segment experienced $145,000 of favorable development.

Other Comprehensive Income

Other Comprehensive Income	3 Months Ended
	Mar. 31, 2018
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Other Comprehensive Income	Other Comprehensive (Loss) Income The following table summarizes the components of other comprehensive income: Three Months Ended 2018 2017 (in thousands) Unrealized (losses) gains arising during the period, before U.S. income taxes $ (19,292 ) $ 5,998 U.S. income taxes 544 (1,636 ) Unrealized (losses) gains arising during the period, net of U.S. income taxes (18,748 ) 4,362 Less reclassification adjustment: Net realized investment (losses) gains (201 ) 450 U.S. income tax expenses — (122 ) Reclassification adjustment for investment (losses) gains realized in net income (201 ) 328 Other comprehensive (loss) income $ (18,547 ) $ 4,034

Contingent Liabilities

Contingent Liabilities	3 Months Ended
	Mar. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Contingent Liabilities	Contingent Liabilities The Company is a party to various lawsuits arising in the ordinary course of its operations. The Company believes that the ultimate resolution of these matters will not materially impact its financial position, cash flows, or results of operations. The Company’s reinsurance subsidiary, JRG Re, has entered into three letter of credit facilities with banks as security to third-party reinsureds on reinsurance assumed by JRG Re. JRG Re has established custodial accounts to secure these letters of credit. Under a $100.0 million facility, $52.2 million of letters of credit were issued through March 31, 2018 which were secured by deposits of $64.2 million . Under a $102.5 million facility, $98.6 million of letters of credit were issued through March 31, 2018 which were secured by deposits of $125.9 million . Under a $100.0 million facility, $6.9 million of letters of credit were issued through March 31, 2018 which were secured by deposits of $10.0 million . JRG Re has also established trust accounts to secure its obligations to selected reinsureds. The total amount deposited in the trust accounts for the benefit of third-party reinsureds was $283.1 million at March 31, 2018 . The Company is also exposed to credit risk relating to a set of insurance contracts with an insured group of companies under which the Company pays losses and loss adjustment expenses on the contract. The Company has indemnity agreements with this group of insured parties (non-insurance entities) and is contractually entitled to receive reimbursement for a significant portion of the losses and loss adjustment expenses paid on behalf of the insured parties and other expenses incurred by the Company. The insured parties are required to collateralize all amounts currently due to the Company and to provide additional collateral sufficient to cover the amounts that may be recoverable under the indemnity agreement, including among other things case loss and loss adjustment expense reserves, IBNR loss and loss adjustment expense reserves, extra contractual obligations and excess of policy limits liabilities. This collateral is currently provided through a collateral trust arrangement established in favor of the Company by a captive insurance company affiliate of the insured group. At March 31, 2018 , the cash equivalent collateral held in the collateral trust arrangement was approximately $860.6 million , which exceeds the amount of claims receivable and unpaid reported losses and loss adjustment expenses outstanding. This is a rapidly growing relationship, and as such, there is ongoing exposure to estimated losses and expenses on these contracts growing at a faster pace than growth in our collateral balances. In addition, we have credit exposure if our estimates of future losses and loss adjustment expenses and other amounts recoverable, which are the basis for establishing collateral balances, are lower than actual amounts paid or payable. The amount of our credit exposure in any of these instances could be material. To mitigate these risks, we closely and frequently monitor our exposure compared to our collateral held, and we request additional collateral when our analysis indicates that we have uncollateralized exposure.

Segment Information

Segment Information	3 Months Ended
	Mar. 31, 2018
Segment Reporting [Abstract]
Segment Information	Segment Information The Company has four reportable segments: the Excess and Surplus Lines segment, the Specialty Admitted Insurance segment, the Casualty Reinsurance segment, and the Corporate and Other segment. Segment profit (loss) is measured by underwriting profit (loss), which is generally defined as net earned premiums less loss and loss adjustment expenses and other operating expenses of the operating segments. Gross fee income of the Excess and Surplus Lines segment is included in that segment’s underwriting profit. For the three months ended March 31, 2018 and 2017 , gross fee income of $4.8 million and $3.8 million , respectively, was included in underwriting profit. Segment results are reported prior to the effects of intercompany reinsurance agreements among the Company’s insurance subsidiaries. The following table summarizes the Company’s segment results: Excess and Specialty Casualty Corporate Total (in thousands) Three Months Ended March 31, 2018 Gross written premiums $ 167,486 $ 87,401 $ 43,229 $ — $ 298,116 Net earned premiums 129,971 13,340 57,631 — 200,942 Underwriting profit of insurance segments 11,299 1,623 1,744 — 14,666 Net investment income 3,042 711 8,017 1,486 13,256 Interest expense — — — 2,522 2,522 Segment revenues 137,327 13,955 65,526 1,536 218,344 Segment goodwill 181,831 — — — 181,831 Segment assets 909,963 495,096 1,368,872 88,079 2,862,010 Three Months Ended March 31, 2017 Gross written premiums $ 108,995 $ 72,464 $ 42,720 $ — $ 224,179 Net earned premiums 93,849 16,253 44,585 — 154,687 Underwriting profit of insurance segments 8,800 842 1,093 — 10,735 Net investment income 3,183 636 7,124 5,790 16,733 Interest expense — — — 2,123 2,123 Segment revenues 101,090 16,924 52,146 6,242 176,402 Segment goodwill 181,831 — — — 181,831 Segment assets 749,617 335,806 1,211,896 114,006 2,411,325 The following table reconciles the underwriting profit of the operating segments by individual segment to consolidated income before taxes: Three Months Ended 2018 2017 (in thousands) Underwriting profit of the insurance segments: Excess and Surplus Lines $ 11,299 $ 8,800 Specialty Admitted Insurance 1,623 842 Casualty Reinsurance 1,744 1,093 Total underwriting profit of insurance segments 14,666 10,735 Other operating expenses of the Corporate and Other segment (7,431 ) (6,461 ) Underwriting profit 7,235 4,274 Net investment income 13,256 16,733 Net realized investment (losses) gains (810 ) 1,047 Amortization of intangible assets (149 ) (149 ) Other income and expenses 104 200 Interest expense (2,522 ) (2,123 ) Income before taxes $ 17,114 $ 19,982

Other Operating Expenses and Ot

Other Operating Expenses and Other Expenses	3 Months Ended
	Mar. 31, 2018
Other Operating Expenses And Other Expenses [Abstract]
Other Operating Expenses and Other Expenses	Other Operating Expenses and Other Expenses Other operating expenses consist of the following: Three Months Ended 2018 2017 (in thousands) Amortization of policy acquisition costs $ 30,198 $ 27,638 Other underwriting expenses of the operating segments 17,154 14,794 Other operating expenses of the Corporate and Other segment 7,431 6,461 Total $ 54,783 $ 48,893

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Three levels of inputs are used to measure fair value of financial instruments: (1) Level 1: quoted price (unadjusted) in active markets for identical assets, (2) Level 2: inputs to the valuation methodology include quoted prices for similar assets and liabilities in active markets, and inputs that are observable for the asset or liability, either directly or indirectly, for substantially the full term of the instrument, and (3) Level 3: inputs to the valuation methodology are unobservable for the asset or liability. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability in the principal or most advantageous market in an orderly transaction between market participants on the measurement date. To measure fair value, the Company obtains quoted market prices for its investment securities from its outside investment managers. If a quoted market price is not available, the Company uses prices of similar securities. Values for U.S. Treasury and publicly-traded equity securities are generally based on Level 1 inputs which use the market approach valuation technique. The values for all other fixed maturity securities (including state and municipal securities and obligations of U.S. government corporations and agencies) generally incorporate significant Level 2 inputs, and in some cases, Level 3 inputs, using the market approach and income approach valuation techniques. There have been no changes in the Company’s use of valuation techniques since December 31, 2016. The Company reviews fair value prices provided by its outside investment managers for reasonableness by comparing the fair values provided by the managers to those provided by its investment custodian. The Company also reviews and monitors changes in unrealized gains and losses. The Company has not historically adjusted security prices. The Company obtains an understanding of the methods, models and inputs used by the investment managers and independent pricing services, and controls are in place to validate that prices provided represent fair values. The Company’s control process includes, but is not limited to, initial and ongoing evaluation of the methodologies used, a review of specific securities and an assessment for proper classification within the fair value hierarchy, and obtaining and reviewing internal control reports for our investment manager that obtains fair values from independent pricing services. Assets measured at fair value on a recurring basis as of March 31, 2018 are summarized below: Fair Value Measurements Using Quoted Prices Significant Significant Total (in thousands) Available-for-sale securities: Fixed maturity securities: State and municipal $ — $ 139,725 $ — $ 139,725 Residential mortgage-backed — 181,098 — 181,098 Corporate — 439,626 — 439,626 Commercial mortgage and asset-backed — 186,124 4,680 190,804 Obligations of U.S. government corporations and agencies — 7,775 — 7,775 U.S. Treasury securities and obligations guaranteed by the U.S. government 81,640 579 — 82,219 Redeemable preferred stock — 2,004 — 2,004 Total fixed maturity securities 81,640 956,931 4,680 1,043,251 Equity securities: Preferred stock — 67,709 — 67,709 Common stock 14,732 3,516 — 18,248 Total equity securities 14,732 71,225 — 85,957 Total available-for-sale securities $ 96,372 $ 1,028,156 $ 4,680 $ 1,129,208 Trading securities: Fixed maturity securities $ — $ 3,805 $ — $ 3,805 Short-term investments $ 1,000 $ 25,235 $ — $ 26,235 Assets measured at fair value on a recurring basis as of December 31, 2017 are summarized below: Fair Value Measurements Using Quoted Prices Significant Significant Total (in thousands) Available-for-sale securities: Fixed maturity securities: State and municipal $ — $ 144,366 $ — $ 144,366 Residential mortgage-backed — 158,661 — 158,661 Corporate — 413,721 — 413,721 Commercial mortgage and asset-backed — 177,931 4,680 182,611 Obligations of U.S. government corporations and agencies — 35,847 — 35,847 U.S. Treasury securities and obligations guaranteed by the U.S. government 78,265 609 — 78,874 Redeemable preferred stock — 2,018 — 2,018 Total fixed maturity securities 78,265 933,153 4,680 1,016,098 Equity securities: Preferred stock — 66,281 — 66,281 Common stock 15,507 734 — 16,241 Total equity securities 15,507 67,015 — 82,522 Total available-for-sale securities $ 93,772 $ 1,000,168 $ 4,680 $ 1,098,620 Trading securities: Fixed maturity securities $ — $ 3,808 $ — $ 3,808 Short-term investments $ 1,000 $ 35,804 $ — $ 36,804 The beginning and ending balances of assets and liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3) consist of one available-for-sale fixed maturity security with a fair value of $4.7 million , and there was no activity (purchases, sales, transfers) involving Level 3 securities for the three months ended March 31, 2018 and 2017 . A market approach using prices in trades of comparable securities was utilized to determine the fair value for this security at March 31, 2018 and December 31, 2017 . Transfers out of Level 3 occur when the Company is able to obtain reliable prices from pricing vendors for securities for which the Company was previously unable to obtain reliable prices. Transfers in to Level 3 occur when the Company is unable to obtain reliable prices for securities from pricing vendors and instead must use broker price quotes to value the securities. There were no transfers between Level 1 and Level 2 during the three months ended March 31, 2018 or 2017 . The Company recognizes transfers between levels at the beginning of the reporting period. There were no realized gains or losses included in earnings for the three months ended March 31, 2018 attributable to the change in unrealized gains or losses relating to Level 3 assets valued at fair value on a recurring basis that are still held at March 31, 2018 . The Company measures certain bank loan participations at fair value on a non-recurring basis during the year as part of the Company’s impairment evaluation when loans are determined by management to be impaired. Assets measured at fair value on a nonrecurring basis are summarized below: Fair Value Measurements Using Quoted Prices Significant Significant Total (in thousands) March 31, 2018 Bank loan participations held-for-investment $ — $ — $ 1,741 $ 1,741 December 31, 2017 Bank loan participations held-for-investment $ — $ — $ 5,111 $ 5,111 Bank loan participations held-for-investment that were determined to be impaired were written down to their fair value of $1.7 million at March 31, 2018 and $5.1 million at December 31, 2017 . In the determination of the fair value for bank loan participations and certain high yield bonds, the Company’s investment manager endeavors to obtain data from multiple external pricing sources. External pricing sources may include brokers, dealers and price data vendors that provide a composite price based on prices from multiple dealers. Such external pricing sources typically provide valuations for normal institutional size trading units of such securities using methods based on market transactions for comparable securities, and various relationships between securities, as generally recognized by institutional dealers. For investments in which the investment manager determines that only one external pricing source is appropriate or if only one external price is available, the relevant investment is generally recorded at fair value based on such price. Investments for which external sources are not available or are determined by the investment manager not to be representative of fair value are recorded at fair value as determined by the Company, with input from its investment managers and valuation specialists as considered necessary. In determining the fair value of such investments, the Company considers one or more of the following factors: type of security held, convertibility or exchangeability of the security, redeemability of the security (including the timing of redemptions), application of industry accepted valuation models, recent trading activity, liquidity, estimates of liquidation value, purchase cost, and prices received for securities with similar terms of the same issuer or similar issuers. At March 31, 2018 , there were no investments for which external sources were unavailable to determine fair value. At December 31, 2017 , there was one bank loan participation with an unpaid principal balance of $807,000 and a carrying value of zero for which external sources were unavailable to determine fair value. The carrying values and fair values of financial instruments are summarized below: March 31, 2018 December 31, 2017 Carrying Fair Value Carrying Fair Value (in thousands) Assets Available-for-sale: Fixed maturity securities $ 1,043,251 $ 1,043,251 $ 1,016,098 $ 1,016,098 Equity securities 85,957 85,957 82,522 82,522 Trading: Fixed maturity securities 3,805 3,805 3,808 3,808 Bank loan participations held-for-investment 257,426 257,840 238,214 236,532 Cash and cash equivalents 151,046 151,046 163,495 163,495 Short-term investments 26,235 26,235 36,804 36,804 Other invested assets – notes receivable 13,250 19,056 11,778 17,104 Liabilities Senior debt 98,300 98,871 98,300 97,884 Junior subordinated debt 104,055 118,752 104,055 116,569 The fair values of fixed maturity securities and equity securities have been determined using quoted market prices for securities traded in the public market or prices using bid or closing prices for securities not traded in the public marketplace. The fair values of cash and cash equivalents and short-term investments approximate their carrying values due to their short-term maturity. The fair values of other invested assets-notes receivable, senior debt, and junior subordinated debt at March 31, 2018 and December 31, 2017 were determined by calculating the present value of expected future cash flows under the terms of the note agreements or debt agreements, as applicable, discounted at an estimated market rate of interest at March 31, 2018 and December 31, 2017 , respectively. The fair values of bank loan participations held-for-investment, senior debt, and junior subordinated debt at March 31, 2018 and December 31, 2017 were determined using inputs to the valuation methodology that are unobservable (Level 3).

Capital Stock and Equity Awards

Capital Stock and Equity Awards	3 Months Ended
	Mar. 31, 2018
Stockholders' Equity Note [Abstract]
Capital Stock and Equity Awards	Capital Stock and Equity Awards The Company issued 170,023 common shares in the three months ended March 31, 2018 with 127,196 new shares related to stock option exercises and 42,827 new shares related to vesting of RSUs. The total common shares outstanding increased from 29,696,682 at December 31, 2017 to 29,866,705 at March 31, 2018 . The Company declared the following dividends during the first three months of 2018 and 2017: Date of Declaration Dividend per Common Share Payable to Shareholders of Record on Payment Date Total Amount 2018 February 22, 2018 $ 0.30 March 12, 2018 March 30, 2018 $ 9.0 million 2017 February 14, 2017 $ 0.30 March 13, 2017 March 31, 2017 $ 8.9 million Included in the dividends are $99,000 and $77,000 of dividend equivalents on RSUs, respectively. The balance of dividends payable was $409,000 at March, 31, 2018 and $434,000 at December 31, 2017. Equity Incentive Plans The Company’s shareholders have approved various equity incentive plans, including the Amended and Restated 2009 Equity Incentive Plan (the “Legacy Plan”), the 2014 Long Term Incentive Plan (“2014 LTIP”), and the 2014 Non-Employee Director Incentive Plan (“2014 Director Plan”) (collectively, the “Plans”). All awards issued under the Plans are issued at the discretion of the Board of Directors. Under the Legacy Plan, employees received non-qualified stock options. Options are outstanding under the Legacy Plan; however, no additional awards may be granted. Employees are eligible to receive non-qualified stock options, incentive stock options, share appreciation rights, performance shares, restricted shares, RSUs, and other awards under the 2014 LTIP. The maximum number of shares available for issuance under the 2014 LTIP is 4,171,150 , and at March 31, 2018 , 1,658,715 shares are available for grant. Non-employee directors of the Company are eligible to receive non-qualified stock options, share appreciation rights, performance shares, restricted shares, restricted share units, and other awards under the 2014 Director Plan. The maximum number of shares available for issuance under the 2014 Director Plan is 50,000 , and at March 31, 2018 , 21,663 shares are available for grant. Generally, awards issued under the 2014 LTIP and 2014 Director Plan vest immediately in the event that an award recipient is terminated without Cause (as defined), and in the case of the 2014 LTIP for Good Reason (as defined), at any time following a Change in Control (as defined in the applicable plans). Options The following table summarizes the option activity for the three months ended March 31, 2018 and 2017: Three Months Ended March 31, 2018 2017 Shares Weighted- Shares Weighted- Outstanding: Beginning of period 1,479,236 $ 27.81 2,234,699 $ 22.84 Granted — $ — 195,509 $ 42.17 Exercised (142,129 ) $ 20.14 (97,211 ) $ 17.23 Forfeited — $ — (50,062 ) $ 27.97 End of period 1,337,107 $ 28.63 2,282,935 $ 24.62 Exercisable, end of period 983,508 $ 26.06 1,334,756 $ 20.47 All of the outstanding options vest over three or four years and have a contractual life of seven years from the original date of grant. All of the outstanding options have an exercise price greater than or equal to the fair value of the underlying shares at the date of grant. The weighted-average remaining contractual life of the options outstanding and options exercisable was 4.4 years and 4.0 years, respectively. RSUs The following table summarizes the RSU activity for the three months ended March 31, 2018 and 2017: Three Months Ended March 31, 2018 2017 Shares Weighted- Shares Weighted- Unvested, beginning of period 178,882 $ 37.93 196,800 $ 24.38 Granted 214,907 $ 39.81 117,879 $ 42.17 Vested (62,714 ) $ 40.90 (37,485 ) $ 32.07 Forfeited — $ — (19,743 ) $ 24.06 Unvested, end of period 331,075 $ 38.59 257,451 $ 31.43 The vesting period of RSUs granted to employees range from one to five years and vest ratably over the respective vesting period, and the majority vest in three years. All RSUs granted to date to non-employee directors had a one year vesting period. The holders of RSUs are entitled to dividend equivalents. The dividend equivalents are settled in cash at the same time that the underlying RSUs vest and are subject to the same risk of forfeiture as the underlying shares. The fair value of the RSUs granted is based on the market price of the underlying shares. Compensation Expense Share based compensation expense is recognized on a straight line basis over the vesting period. The amount of expense and related tax benefit is summarized below: Three Months Ended 2018 2017 (in thousands) Share based compensation expense $ 1,455 $ 1,794 U.S. tax benefit on share based compensation expense 173 469 As of March 31, 2018 , the Company had $14.0 million of unrecognized share based compensation expense expected to be charged to earnings over a weighted-average period of 2.3 years.

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2018
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events On May 1, 2018 , the Board of Directors declared a cash dividend of $0.30 per common share. The dividend is payable on June 29, 2018 to shareholders of record on June 11, 2018 .

Accounting Policies (Policies)

Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed consolidated financial statements and notes have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information and do not contain all of the information and footnotes required by U.S. GAAP for complete financial statements. The condensed consolidated financial statements include the results of the Company and its subsidiaries from their respective dates of inception or acquisition, as applicable. Readers are urged to review the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 for a more complete description of the Company’s business and accounting policies. In the opinion of management, all adjustments necessary for a fair presentation of the condensed consolidated financial statements have been included. Such adjustments consist only of normal recurring items. Interim results are not necessarily indicative of results of operations for the full year. The consolidated balance sheet as of December 31, 2017 was derived from the Company’s audited annual consolidated financial statements. Intercompany transactions and balances have been eliminated.
Estimates and Assumptions	Estimates and Assumptions Preparation of the condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the condensed consolidated financial statements and accompanying disclosures. Those estimates are inherently subject to change, and actual results may ultimately differ from those estimates.
Variable Interest Entities	Variable Interest Entities Entities that do not have sufficient equity at risk to allow the entity to finance its activities without additional financial support or in which the equity investors, as a group, do not have the characteristic of a controlling financial interest are referred to as variable interest entities (“VIE”). A VIE is consolidated by the variable interest holder that is determined to have the controlling financial interest (primary beneficiary) as a result of having both the power to direct the activities of a VIE that most significantly impact the VIE’s economic performance and the obligation to absorb losses or the right to receive benefits from the VIE that could potentially be significant to the VIE. The Company determines whether it is the primary beneficiary of an entity subject to consolidation based on a qualitative assessment of the VIE’s capital structure, contractual terms, nature of the VIE’s operations and purpose, and the Company’s relative exposure to the related risks of the VIE on the date it becomes initially involved in the VIE. The Company reassesses its VIE determination with respect to an entity on an ongoing basis. The Company holds interests in VIEs through certain equity method investments included in “other invested assets” in the accompanying condensed consolidated balance sheets. The Company has determined that it should not consolidate any of the VIEs as it is not the primary beneficiary in any of the relationships. Although the investments resulted in the Company holding variable interests in the entities, they did not empower the Company to direct the activities that most significantly impact the economic performance of the entities.
Income Tax Expense	Income Tax Expense Our effective tax rate fluctuates from period to period based on the relative mix of income reported by country and the respective tax rates imposed by each tax jurisdiction. For the three months ended March 31, 2018 and 2017 , our U.S. federal income tax expense was 8.7% and 7.7% of income before taxes, respectively. For U.S.-sourced income, the Company’s U.S. federal income tax expense differs from the amounts computed by applying the federal statutory income tax rate (21% in 2018 and 35% in 2017) to income before taxes due primarily to interest income on tax-advantaged state and municipal securities (state and municipal securities represent 12.4% and 10.9% of our available-for-sale securities at March 31, 2018 and 2017 , respectively), dividends received income, and excess tax benefits on share based compensation.
Adopted Accounting Standards	Adopted Accounting Standards Effective January 1, 2018, the Company adopted Accounting Standards Update (“ASU”) 2014-09, Revenue from Contracts with Customers (Topic 606) . The guidance applies to all companies that either enter into contracts with customers to transfer goods or services or enter into contracts for the transfer of nonfinancial assets, unless those contracts are within the scope of other standards, such as insurance contracts. Under this guidance, a company will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. Judgments required in adopting this update may include identifying performance obligations in the contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. The adoption of ASU 2014-09 had no impact on reported fee income and there was no cumulative effect of initially applying the update. Effective January 1, 2018, the Company adopted ASU 2016-01, Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities . Among other things, this ASU 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. Upon adoption on January 1, 2018, the Company made a $4.7 million cumulative-effect adjustment to increase retained earnings and reduce accumulated other comprehensive income. The adoption of ASU 2016-01 did not materially impact the Company's financial position, cash flows, or total comprehensive income. The Company's results of operations were impacted as changes in fair value of equity instruments are now presented in net income rather than other comprehensive (loss) income. For the three months ended March 31, 2018, the impact was a $1.4 million reduction in net income and a $0.05 reduction in basic and diluted earnings per share. Effective January 1, 2018, the Company adopted ASU 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. This update was issued as a result of the enactment of the TCJA on December 22, 2017. The ASU allows for the option to reclassify the stranded tax effects resulting from the implementation of the TCJA out of accumulated other comprehensive income and into retained earnings. As the adoption of ASU 2016-01 in 2018 resulted in the reclassification of the entire unrealized balance on equity securities from accumulated other comprehensive income into retained earnings, only the stranded tax effects on the unrealized balances of fixed income securities were impacted by the adoption of ASU 2018-02. The reclassification resulted in a $711,000 decrease to the Company's retained earnings with a corresponding increase to accumulated other comprehensive income in the first quarter of 2018.
Prospective Accounting Standards	Prospective Accounting Standards In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) . Under current guidance for lessees, leases are only included on the balance sheet if certain criteria, classifying the agreement as a capital lease, are met. This update will require the recognition of a right-of-use asset and a corresponding lease liability, discounted to the present value, for all leases that extend beyond 12 months. This ASU is effective for annual and interim reporting periods beginning after December 15, 2018. Upon adoption, leases will be recognized and measured at the beginning of the earliest period presented using a modified retrospective approach. The Company is currently evaluating ASU 2016-02 to determine the potential impact that adopting this standard will have on its financial statements. In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. Current GAAP delays the recognition of credit losses until it is probable a loss has been incurred. The update will require financial assets measured at amortized cost, such as bank loan participations held for investment, to be presented at the net amount expected to be collected by means of an allowance for credit losses that runs through net income. Credit losses relating to available-for-sale debt securities will also be recorded through an allowance for credit losses, with the amount of the allowance limited to the amount by which fair value is below amortized cost. This ASU is effective for annual and interim reporting periods beginning after December 15, 2019. Upon adoption, this ASU will be applied using the modified-retrospective approach, by which a cumulative-effect adjustment will be made to retained earnings as of the beginning of the first reporting period presented. The Company has not yet completed the analysis of how adopting this ASU will affect the Company’s financial statements.

Investments (Tables)

Investments (Tables)	3 Months Ended
	Mar. 31, 2018
Investments [Abstract]
Schedule of summary of available-for-sale investments	The Company’s available-for-sale investments are summarized as follows: Cost or Gross Gross Fair (in thousands) March 31, 2018 Fixed maturity securities: State and municipal $ 137,478 $ 4,029 $ (1,782 ) $ 139,725 Residential mortgage-backed 186,279 509 (5,690 ) 181,098 Corporate 445,058 3,054 (8,486 ) 439,626 Commercial mortgage and asset-backed 192,941 173 (2,310 ) 190,804 Obligations of U.S. government corporations and agencies 7,804 — (29 ) 7,775 U.S. Treasury securities and obligations guaranteed by the U.S. government 83,317 73 (1,171 ) 82,219 Redeemable preferred stock 2,025 — (21 ) 2,004 Total fixed maturity securities 1,054,902 7,838 (19,489 ) 1,043,251 Equity securities 80,464 6,845 (1,352 ) 85,957 Total investments available-for-sale $ 1,135,366 $ 14,683 $ (20,841 ) $ 1,129,208 December 31, 2017 Fixed maturity securities: State and municipal $ 139,382 $ 5,587 $ (603 ) $ 144,366 Residential mortgage-backed 160,379 723 (2,441 ) 158,661 Corporate 408,857 7,503 (2,639 ) 413,721 Commercial mortgage and asset-backed 182,595 714 (698 ) 182,611 Obligations of U.S. government corporations and agencies 35,948 — (101 ) 35,847 U.S. Treasury securities and obligations guaranteed by the U.S. government 79,476 37 (639 ) 78,874 Redeemable preferred stock 2,025 — (7 ) 2,018 Total fixed maturity securities 1,008,662 14,564 (7,128 ) 1,016,098 Equity securities 75,318 7,830 (626 ) 82,522 Total investments available-for-sale $ 1,083,980 $ 22,394 $ (7,754 ) $ 1,098,620
Schedule of summary of available-for-sale investments by contractual maturity	The amortized cost and fair value of available-for-sale investments in fixed maturity securities at March 31, 2018 are summarized, by contractual maturity, as follows: Cost or Fair (in thousands) One year or less $ 33,850 $ 33,743 After one year through five years 327,069 323,368 After five years through ten years 185,400 181,026 After ten years 127,338 131,208 Residential mortgage-backed 186,279 181,098 Commercial mortgage and asset-backed 192,941 190,804 Redeemable preferred stock 2,025 2,004 Total $ 1,054,902 $ 1,043,251
Schedule of gross unrealized losses and fair value for available-for-sale securities	The following table shows the Company’s gross unrealized losses and fair value for available-for-sale securities aggregated by investment category and the length of time that individual securities have been in a continuous unrealized loss position: Less Than 12 Months 12 Months or More Total Fair Gross Fair Gross Fair Gross (in thousands) March 31, 2018 Fixed maturity securities: State and municipal $ 61,275 $ (1,325 ) $ 10,454 $ (457 ) $ 71,729 $ (1,782 ) Residential mortgage-backed 90,188 (1,743 ) 79,455 (3,947 ) 169,643 (5,690 ) Corporate 260,523 (5,309 ) 64,506 (3,177 ) 325,029 (8,486 ) Commercial mortgage and asset-backed 94,429 (1,578 ) 22,658 (732 ) 117,087 (2,310 ) Obligations of U.S. government corporations and agencies — — 7,775 (29 ) 7,775 (29 ) U.S. Treasury securities and obligations guaranteed by the U.S. government 53,118 (913 ) 18,080 (258 ) 71,198 (1,171 ) Redeemable preferred stock 2,004 (21 ) — — 2,004 (21 ) Total fixed maturity securities 561,537 (10,889 ) 202,928 (8,600 ) 764,465 (19,489 ) Equity securities 17,816 (811 ) 5,685 (541 ) 23,501 (1,352 ) Total investments available-for-sale $ 579,353 $ (11,700 ) $ 208,613 $ (9,141 ) $ 787,966 $ (20,841 ) December 31, 2017 Fixed maturity securities: State and municipal $ 40,117 $ (318 ) $ 10,662 $ (285 ) $ 50,779 $ (603 ) Residential mortgage-backed 50,447 (261 ) 84,193 (2,180 ) 134,640 (2,441 ) Corporate 113,464 (846 ) 66,954 (1,793 ) 180,418 (2,639 ) Commercial mortgage and asset-backed 53,965 (244 ) 25,299 (454 ) 79,264 (698 ) Obligations of U.S. government corporations and agencies 3,024 (1 ) 32,154 (100 ) 35,178 (101 ) U.S. Treasury securities and obligations guaranteed by the U.S. government 50,760 (430 ) 26,707 (209 ) 77,467 (639 ) Redeemable preferred stock 2,018 (7 ) — — 2,018 (7 ) Total fixed maturity securities 313,795 (2,107 ) 245,969 (5,021 ) 559,764 (7,128 ) Equity securities 5,859 (65 ) 5,665 (561 ) 11,524 (626 ) Total investments available-for-sale $ 319,654 $ (2,172 ) $ 251,634 $ (5,582 ) $ 571,288 $ (7,754 )
Schedule of summary of realized gains and losses	The Company’s realized gains and losses are summarized as follows: Three Months Ended 2018 2017 (in thousands) Fixed maturity securities: Gross realized gains $ 22 $ 338 Gross realized losses (223 ) (296 ) (201 ) 42 Bank loan participations: Gross realized gains 1,220 1,136 Gross realized losses (100 ) (539 ) 1,120 597 Equity securities: Gross realized gains — 409 Gross realized losses (15 ) — Changes in fair values of equity securities (1,710 ) — (1,725 ) 409 Short-term investments and other: Gross realized gains — — Gross realized losses (4 ) (1 ) (4 ) (1 ) Total $ (810 ) $ 1,047
Schedule of other invested assets	The Company invests selectively in private debt and equity opportunities. These investments, which together comprise the Company’s other invested assets, are primarily focused in renewable energy, limited partnerships, and bank holding companies. Carrying Value Investment Income March 31, December 31, Three Months Ended 2018 2017 2018 2017 (in thousands) Renewable energy LLCs (a) $ 32,592 $ 32,063 $ 1,211 $ 5,594 Renewable energy notes receivable ( b) 8,750 7,278 297 — Limited partnerships (c) 29,132 26,367 226 382 Bank holding companies (d) 4,500 4,500 86 86 Total other invested assets $ 74,974 $ 70,208 $ 1,820 $ 6,062 (a) The Company’s Corporate and Other segment owns equity interests ranging from 2.6% to 32.8% in various LLCs whose principal objective is capital appreciation and income generation from owning and operating renewable energy production facilities (wind and solar). The LLCs are managed by an affiliate of the Company’s largest shareholder and the Company’s Non-Exucitive Chairman has invested in certain of these LLCs. The equity method is used to account for the Company’s LLC investments. Income for the LLCs primarily reflects adjustments to the carrying values of investments in renewable energy projects to their determined fair values. The fair value adjustments are included in revenues for the LLCs. Expenses for the LLCs are not significant and are comprised of administrative and interest expenses. The Company received cash distributions from these investments totaling $1.2 million and $1.6 million in the three months ended March 31, 2018 and 2017 , respectively. (b) The Company has invested in notes receivable for renewable energy projects. At March 31, 2018 , the Company holds an $8.8 million note issued by an affiliate of the Company’s largest shareholder. Interest on the note, which matures in 2021, is fixed at 15.0% . Interest income on the note was $297,000 for the three months ended March 31, 2018 . (c) The Company owns investments in limited partnerships that invest in concentrated portfolios including publicly-traded small cap equities, loans of middle market private equity sponsored companies, equity tranches of collateralized loan obligations ( “ CLOs ” ), and tranches of distressed home loans. Income f rom the partnerships is recognized under the equity method of accounting. The Company’s Corporate and Other segment held an investment in a limited partnership with a carrying value of $2.9 million at March 31, 2018 . The Company recognized investment losses of $125,000 and investment income of $68,000 on the investment for the three months ended March 31, 2018 and 2017 , respectively. The Company’s Excess and Surplus Lines segment holds investments in limited partnerships of $26.3 million at March 31, 2018 . Investment income of $351,000 and $314,000 was recognized on the investments for the three months ended March 31, 2018 and 2017 , respectively. At March 31, 2018 , the Company’s Excess and Surplus Lines segment has outstanding commitments to invest another $2.6 million in these limited partnerships. (d) The Company holds $4.5 million of subordinated notes issued by a bank holding company. Interest on the notes, which mature on August 12, 2023, is fixed at 7.6% per annum. Interest income on the notes was $86,000 in both three months ended March 31, 2018 and 2017 . The Company’s Chairman was previously the Lead Independent Director of the bank holding company and an investor in the bank holding company. Additionally, one of the Company’s directors was an investor in the bank holding company and is currently a lender to the bank holding company.

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	3 Months Ended
	Mar. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of gross carrying amounts and accumulated amortization	The gross carrying amounts and accumulated amortization for each major specifically identifiable intangible asset class were as follows: March 31, 2018 December 31, 2017 Life Gross Accumulated Gross Accumulated ($ in thousands) Intangible Assets Trademarks Indefinite $ 22,200 $ — $ 22,200 $ — Insurance licenses and authorities Indefinite 9,164 — 9,164 — Identifiable intangibles not subject to amortization 31,364 — 31,364 — Broker relationships 24.6 11,611 4,790 11,611 4,641 Identifiable intangible assets subject to amortization 11,611 4,790 11,611 4,641 $ 42,975 $ 4,790 $ 42,975 $ 4,641

Earnings Per Share (Tables)

Earnings Per Share (Tables)	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Schedule of reconciliation of numerator and denominator of basic and diluted earnings per share	The following represents a reconciliation of the numerator and denominator of the basic and diluted earnings per share computations contained in the condensed consolidated financial statements: Three Months Ended 2018 2017 (in thousands, except share and per share amounts) Net income to shareholders $ 15,633 $ 18,450 Weighted average common shares outstanding: Basic 29,764,320 29,289,588 Common share equivalents 428,983 1,037,835 Diluted 30,193,303 30,327,423 Earnings per share: Basic $ 0.53 $ 0.63 Common share equivalents (0.01 ) (0.02 ) Diluted $ 0.52 $ 0.61

Reserve for Losses and Loss A24

Reserve for Losses and Loss Adjustment Expenses (Tables)	3 Months Ended
	Mar. 31, 2018
Liability for Claims and Claims Adjustment Expense [Abstract]
Schedule of reconciliation of beginning and ending reserve balances for losses and loss adjustment expenses	The following table provides a reconciliation of the beginning and ending reserve balances for losses and loss adjustment expenses, net of reinsurance, to the gross amounts reported in the condensed consolidated balance sheets: Three Months Ended 2018 2017 (in thousands) Reserve for losses and loss adjustment expenses net of reinsurance recoverables at beginning of period $ 989,825 $ 761,128 Add: Incurred losses and loss adjustment expenses net of reinsurance: Current year 146,382 108,783 Prior years (2,610 ) (3,414 ) Total incurred losses and loss and adjustment expenses 143,772 105,369 Deduct: Loss and loss adjustment expense payments net of reinsurance: Current year 12,177 3,698 Prior years 83,117 71,018 Total loss and loss adjustment expense payments 95,294 74,716 Reserve for losses and loss adjustment expenses net of reinsurance recoverables at end of period 1,038,303 791,781 Add: Reinsurance recoverables on unpaid losses and loss adjustment expenses at end of period 331,245 188,782 Reserve for losses and loss adjustment expenses gross of reinsurance recoverables on unpaid losses and loss adjustment expenses at end of period $ 1,369,548 $ 980,563

Other Comprehensive Income (Tab

Other Comprehensive Income (Tables)	3 Months Ended
	Mar. 31, 2018
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Schedule of components of comprehensive income	The following table summarizes the components of other comprehensive income: Three Months Ended 2018 2017 (in thousands) Unrealized (losses) gains arising during the period, before U.S. income taxes $ (19,292 ) $ 5,998 U.S. income taxes 544 (1,636 ) Unrealized (losses) gains arising during the period, net of U.S. income taxes (18,748 ) 4,362 Less reclassification adjustment: Net realized investment (losses) gains (201 ) 450 U.S. income tax expenses — (122 ) Reclassification adjustment for investment (losses) gains realized in net income (201 ) 328 Other comprehensive (loss) income $ (18,547 ) $ 4,034

Segment Information (Tables)

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2018
Segment Reporting [Abstract]
Schedule of summary of company's segment results	The following table summarizes the Company’s segment results: Excess and Specialty Casualty Corporate Total (in thousands) Three Months Ended March 31, 2018 Gross written premiums $ 167,486 $ 87,401 $ 43,229 $ — $ 298,116 Net earned premiums 129,971 13,340 57,631 — 200,942 Underwriting profit of insurance segments 11,299 1,623 1,744 — 14,666 Net investment income 3,042 711 8,017 1,486 13,256 Interest expense — — — 2,522 2,522 Segment revenues 137,327 13,955 65,526 1,536 218,344 Segment goodwill 181,831 — — — 181,831 Segment assets 909,963 495,096 1,368,872 88,079 2,862,010 Three Months Ended March 31, 2017 Gross written premiums $ 108,995 $ 72,464 $ 42,720 $ — $ 224,179 Net earned premiums 93,849 16,253 44,585 — 154,687 Underwriting profit of insurance segments 8,800 842 1,093 — 10,735 Net investment income 3,183 636 7,124 5,790 16,733 Interest expense — — — 2,123 2,123 Segment revenues 101,090 16,924 52,146 6,242 176,402 Segment goodwill 181,831 — — — 181,831 Segment assets 749,617 335,806 1,211,896 114,006 2,411,325
Schedule of underwriting profit of operating segments by individual segment and reconciliation to consolidated income before taxes	The following table reconciles the underwriting profit of the operating segments by individual segment to consolidated income before taxes: Three Months Ended 2018 2017 (in thousands) Underwriting profit of the insurance segments: Excess and Surplus Lines $ 11,299 $ 8,800 Specialty Admitted Insurance 1,623 842 Casualty Reinsurance 1,744 1,093 Total underwriting profit of insurance segments 14,666 10,735 Other operating expenses of the Corporate and Other segment (7,431 ) (6,461 ) Underwriting profit 7,235 4,274 Net investment income 13,256 16,733 Net realized investment (losses) gains (810 ) 1,047 Amortization of intangible assets (149 ) (149 ) Other income and expenses 104 200 Interest expense (2,522 ) (2,123 ) Income before taxes $ 17,114 $ 19,982

Other Operating Expenses and 27

Other Operating Expenses and Other Expenses (Tables)	3 Months Ended
	Mar. 31, 2018
Other Operating Expenses And Other Expenses [Abstract]
Schedule of other operating expenses	Other operating expenses consist of the following: Three Months Ended 2018 2017 (in thousands) Amortization of policy acquisition costs $ 30,198 $ 27,638 Other underwriting expenses of the operating segments 17,154 14,794 Other operating expenses of the Corporate and Other segment 7,431 6,461 Total $ 54,783 $ 48,893

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Schedule of assets measured at fair value on a recurring basis	Assets measured at fair value on a recurring basis as of March 31, 2018 are summarized below: Fair Value Measurements Using Quoted Prices Significant Significant Total (in thousands) Available-for-sale securities: Fixed maturity securities: State and municipal $ — $ 139,725 $ — $ 139,725 Residential mortgage-backed — 181,098 — 181,098 Corporate — 439,626 — 439,626 Commercial mortgage and asset-backed — 186,124 4,680 190,804 Obligations of U.S. government corporations and agencies — 7,775 — 7,775 U.S. Treasury securities and obligations guaranteed by the U.S. government 81,640 579 — 82,219 Redeemable preferred stock — 2,004 — 2,004 Total fixed maturity securities 81,640 956,931 4,680 1,043,251 Equity securities: Preferred stock — 67,709 — 67,709 Common stock 14,732 3,516 — 18,248 Total equity securities 14,732 71,225 — 85,957 Total available-for-sale securities $ 96,372 $ 1,028,156 $ 4,680 $ 1,129,208 Trading securities: Fixed maturity securities $ — $ 3,805 $ — $ 3,805 Short-term investments $ 1,000 $ 25,235 $ — $ 26,235 Assets measured at fair value on a recurring basis as of December 31, 2017 are summarized below: Fair Value Measurements Using Quoted Prices Significant Significant Total (in thousands) Available-for-sale securities: Fixed maturity securities: State and municipal $ — $ 144,366 $ — $ 144,366 Residential mortgage-backed — 158,661 — 158,661 Corporate — 413,721 — 413,721 Commercial mortgage and asset-backed — 177,931 4,680 182,611 Obligations of U.S. government corporations and agencies — 35,847 — 35,847 U.S. Treasury securities and obligations guaranteed by the U.S. government 78,265 609 — 78,874 Redeemable preferred stock — 2,018 — 2,018 Total fixed maturity securities 78,265 933,153 4,680 1,016,098 Equity securities: Preferred stock — 66,281 — 66,281 Common stock 15,507 734 — 16,241 Total equity securities 15,507 67,015 — 82,522 Total available-for-sale securities $ 93,772 $ 1,000,168 $ 4,680 $ 1,098,620 Trading securities: Fixed maturity securities $ — $ 3,808 $ — $ 3,808 Short-term investments $ 1,000 $ 35,804 $ — $ 36,804
Schedule of assets measured at fair value on a nonrecurring basis	Assets measured at fair value on a nonrecurring basis are summarized below: Fair Value Measurements Using Quoted Prices Significant Significant Total (in thousands) March 31, 2018 Bank loan participations held-for-investment $ — $ — $ 1,741 $ 1,741 December 31, 2017 Bank loan participations held-for-investment $ — $ — $ 5,111 $ 5,111
Schedule of carrying value and fair value	The carrying values and fair values of financial instruments are summarized below: March 31, 2018 December 31, 2017 Carrying Fair Value Carrying Fair Value (in thousands) Assets Available-for-sale: Fixed maturity securities $ 1,043,251 $ 1,043,251 $ 1,016,098 $ 1,016,098 Equity securities 85,957 85,957 82,522 82,522 Trading: Fixed maturity securities 3,805 3,805 3,808 3,808 Bank loan participations held-for-investment 257,426 257,840 238,214 236,532 Cash and cash equivalents 151,046 151,046 163,495 163,495 Short-term investments 26,235 26,235 36,804 36,804 Other invested assets – notes receivable 13,250 19,056 11,778 17,104 Liabilities Senior debt 98,300 98,871 98,300 97,884 Junior subordinated debt 104,055 118,752 104,055 116,569

Capital Stock and Equity Awar29

Capital Stock and Equity Awards (Tables)	3 Months Ended
	Mar. 31, 2018
Stockholders' Equity Note [Abstract]
Schedule of dividends	The Company declared the following dividends during the first three months of 2018 and 2017: Date of Declaration Dividend per Common Share Payable to Shareholders of Record on Payment Date Total Amount 2018 February 22, 2018 $ 0.30 March 12, 2018 March 30, 2018 $ 9.0 million 2017 February 14, 2017 $ 0.30 March 13, 2017 March 31, 2017 $ 8.9 million
Schedule of summary of option activity	The following table summarizes the option activity for the three months ended March 31, 2018 and 2017: Three Months Ended March 31, 2018 2017 Shares Weighted- Shares Weighted- Outstanding: Beginning of period 1,479,236 $ 27.81 2,234,699 $ 22.84 Granted — $ — 195,509 $ 42.17 Exercised (142,129 ) $ 20.14 (97,211 ) $ 17.23 Forfeited — $ — (50,062 ) $ 27.97 End of period 1,337,107 $ 28.63 2,282,935 $ 24.62 Exercisable, end of period 983,508 $ 26.06 1,334,756 $ 20.47
Schedule of summary of RSU activity	The following table summarizes the RSU activity for the three months ended March 31, 2018 and 2017: Three Months Ended March 31, 2018 2017 Shares Weighted- Shares Weighted- Unvested, beginning of period 178,882 $ 37.93 196,800 $ 24.38 Granted 214,907 $ 39.81 117,879 $ 42.17 Vested (62,714 ) $ 40.90 (37,485 ) $ 32.07 Forfeited — $ — (19,743 ) $ 24.06 Unvested, end of period 331,075 $ 38.59 257,451 $ 31.43
Schedule of summary of amount of expense and related tax benefit	Share based compensation expense is recognized on a straight line basis over the vesting period. The amount of expense and related tax benefit is summarized below: Three Months Ended 2018 2017 (in thousands) Share based compensation expense $ 1,455 $ 1,794 U.S. tax benefit on share based compensation expense 173 469

Accounting Policies - Narrative

Accounting Policies - Narrative (Details) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)company$ / shares	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of insurance companies based in the United States | company	6
Investment in variable interest entities	$ 32,600		$ 32,100
Effective U.S. federal income tax expense rate	8.70%	7.70%
Percentage of available for sale securities	12.40%	10.90%
Net income	$ (15,633)	$ (18,450)
ASU 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of adoption of ASU	0
ASU 2018-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of adoption of ASU	0
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net income	(15,633)	$ (18,450)
Retained Earnings | ASU 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of adoption of ASU	4,682
Net income	$ 1,400
Reduction in basic and diluted earnings per share | $ / shares	$ 0.05
Retained Earnings | ASU 2018-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of adoption of ASU	$ (711)

Investments - Narrative (Detail

Investments - Narrative (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018USD ($)issuerloan	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)loan	Dec. 31, 2016USD ($)
Gain (Loss) on Investments [Line Items]
Number of available-for-sale securities held in an unrealized loss position | issuer	205
Total fair value of unrealized loss position securities	$ 787,966		$ 571,288
Total gross unrealized losses of unrealized loss position securities	$ 20,841		7,754
Percentage of available for sale securities	12.40%	10.90%
Fair value	$ 1,129,208		1,098,620
Impairment loss			1,500
Unpaid principal on impaired loans	2,100		8,400
Carrying value of loan	257,426		238,214
Allowance for credit losses on impaired loans	$ 300	$ 639	$ 3,200	$ 943
Number of impaired loans held | loan	2		5
Carrying value of impaired loans	$ 1,700		$ 5,100
Average recorded investment in impaired bank loans	3,400	5,300
Investment income during period loans were impaired	20	84
Net realized gain (loss) on changes in fair value of impaired bank loans	3	177
Net trading gains (losses) still held	3
Carrying value of collateralized loan obligation held	4,700
Net realized investment (losses) gains	(810)	1,047
Investment income	1,820	6,062
Bank Holding Company
Gain (Loss) on Investments [Line Items]
Net realized investment (losses) gains	409
Investment in certificate of deposit	1,000
Interest income	0	1
Fixed maturity securities
Gain (Loss) on Investments [Line Items]
Total fair value of unrealized loss position securities	764,465		559,764
Total gross unrealized losses of unrealized loss position securities	19,489		7,128
Fair value	1,043,251		1,016,098
Net realized investment (losses) gains	(201)	$ 42
Puerto Rico loan
Gain (Loss) on Investments [Line Items]
Unpaid principal on impaired loans	807
Carrying value of loan	0
Net realized investment (losses) gains	807
Oil and gas companies loan
Gain (Loss) on Investments [Line Items]
Unpaid principal on impaired loans	2,100		6,900
Carrying value of loan	4,700
Allowance for credit losses on impaired loans	$ 300		$ 2,300
Number of loans | loan	3
Bank loan participations gross unrealized losses	$ 143
Number of impaired loans held | loan	2		3
Carrying value of impaired loans	$ 1,700		$ 4,600
Non-energy sector loan
Gain (Loss) on Investments [Line Items]
Unpaid principal on impaired loans			706
Allowance for credit losses on impaired loans			$ 145
Number of impaired loans held | loan			1
Carrying value of impaired loans			$ 561
BBB- or better | Fixed maturity securities
Gain (Loss) on Investments [Line Items]
Percentage of available for sale securities	99.90%
Fair value	$ 868
Aggregate net unrealized gain (loss)	$ (26)

Investments - Schedule of Avail

Investments - Schedule of Available-for-Sale Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	$ 1,135,366	$ 1,083,980
Gross Unrealized Gains	14,683	22,394
Gross Unrealized Losses	(20,841)	(7,754)
Fair Value	1,129,208	1,098,620
Fixed maturity securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	1,054,902	1,008,662
Gross Unrealized Gains	7,838	14,564
Gross Unrealized Losses	(19,489)	(7,128)
Fair Value	1,043,251	1,016,098
State and municipal
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	137,478	139,382
Gross Unrealized Gains	4,029	5,587
Gross Unrealized Losses	(1,782)	(603)
Fair Value	139,725	144,366
Residential mortgage-backed
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	186,279	160,379
Gross Unrealized Gains	509	723
Gross Unrealized Losses	(5,690)	(2,441)
Fair Value	181,098	158,661
Corporate
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	445,058	408,857
Gross Unrealized Gains	3,054	7,503
Gross Unrealized Losses	(8,486)	(2,639)
Fair Value	439,626	413,721
Commercial mortgage and asset-backed
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	192,941	182,595
Gross Unrealized Gains	173	714
Gross Unrealized Losses	(2,310)	(698)
Fair Value	190,804	182,611
Obligations of U.S. government corporations and agencies
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	7,804	35,948
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(29)	(101)
Fair Value	7,775	35,847
U.S. Treasury securities and obligations guaranteed by the U.S. government
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	83,317	79,476
Gross Unrealized Gains	73	37
Gross Unrealized Losses	(1,171)	(639)
Fair Value	82,219	78,874
Redeemable preferred stock
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	2,025	2,025
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(21)	(7)
Fair Value	2,004	2,018
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	80,464	75,318
Gross Unrealized Gains	6,845	7,830
Gross Unrealized Losses	(1,352)	(626)
Fair Value	$ 85,957	$ 82,522

Investments - Schedule of Contr

Investments - Schedule of Contract Maturities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Cost or Amortized Cost
One year or less	$ 33,850
After one year through five years	327,069
After five years through ten years	185,400
After ten years	127,338
Residential mortgage-backed	186,279
Commercial mortgage and asset-backed	192,941
Redeemable preferred stock	2,025
Total	1,054,902	$ 1,008,662
Fair Value
One year or less	33,743
After one year through five years	323,368
After five years through ten years	181,026
After ten years	131,208
Residential mortgage-backed	181,098
Commercial mortgage and asset-backed	190,804
Redeemable preferred stock	2,004
Total	$ 1,043,251	$ 1,016,098

Investments - Schedule of Gross

Investments - Schedule of Gross Unrealized Losses and Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	$ 579,353	$ 319,654
Less Than 12 Months, Gross Unrealized Losses	(11,700)	(2,172)
12 Months or More, Fair Value	208,613	251,634
12 Months or More, Gross Unrealized Losses	(9,141)	(5,582)
Total, Fair Value	787,966	571,288
Total, Gross Unrealized Losses	(20,841)	(7,754)
Fixed maturity securities
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	561,537	313,795
Less Than 12 Months, Gross Unrealized Losses	(10,889)	(2,107)
12 Months or More, Fair Value	202,928	245,969
12 Months or More, Gross Unrealized Losses	(8,600)	(5,021)
Total, Fair Value	764,465	559,764
Total, Gross Unrealized Losses	(19,489)	(7,128)
State and municipal
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	61,275	40,117
Less Than 12 Months, Gross Unrealized Losses	(1,325)	(318)
12 Months or More, Fair Value	10,454	10,662
12 Months or More, Gross Unrealized Losses	(457)	(285)
Total, Fair Value	71,729	50,779
Total, Gross Unrealized Losses	(1,782)	(603)
Residential mortgage-backed
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	90,188	50,447
Less Than 12 Months, Gross Unrealized Losses	(1,743)	(261)
12 Months or More, Fair Value	79,455	84,193
12 Months or More, Gross Unrealized Losses	(3,947)	(2,180)
Total, Fair Value	169,643	134,640
Total, Gross Unrealized Losses	(5,690)	(2,441)
Corporate
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	260,523	113,464
Less Than 12 Months, Gross Unrealized Losses	(5,309)	(846)
12 Months or More, Fair Value	64,506	66,954
12 Months or More, Gross Unrealized Losses	(3,177)	(1,793)
Total, Fair Value	325,029	180,418
Total, Gross Unrealized Losses	(8,486)	(2,639)
Commercial mortgage and asset-backed
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	94,429	53,965
Less Than 12 Months, Gross Unrealized Losses	(1,578)	(244)
12 Months or More, Fair Value	22,658	25,299
12 Months or More, Gross Unrealized Losses	(732)	(454)
Total, Fair Value	117,087	79,264
Total, Gross Unrealized Losses	(2,310)	(698)
Obligations of U.S. government corporations and agencies
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	0	3,024
Less Than 12 Months, Gross Unrealized Losses	0	(1)
12 Months or More, Fair Value	7,775	32,154
12 Months or More, Gross Unrealized Losses	(29)	(100)
Total, Fair Value	7,775	35,178
Total, Gross Unrealized Losses	(29)	(101)
U.S. Treasury securities and obligations guaranteed by the U.S. government
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	53,118	50,760
Less Than 12 Months, Gross Unrealized Losses	(913)	(430)
12 Months or More, Fair Value	18,080	26,707
12 Months or More, Gross Unrealized Losses	(258)	(209)
Total, Fair Value	71,198	77,467
Total, Gross Unrealized Losses	(1,171)	(639)
Redeemable preferred stock
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	2,004	2,018
Less Than 12 Months, Gross Unrealized Losses	(21)	(7)
12 Months or More, Fair Value	0	0
12 Months or More, Gross Unrealized Losses	0	0
Total, Fair Value	2,004	2,018
Total, Gross Unrealized Losses	(21)	(7)
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	17,816	5,859
Less Than 12 Months, Gross Unrealized Losses	(811)	(65)
12 Months or More, Fair Value	5,685	5,665
12 Months or More, Gross Unrealized Losses	(541)	(561)
Total, Fair Value	23,501	11,524
Total, Gross Unrealized Losses	$ (1,352)	$ (626)

Investments - Summary of Realiz

Investments - Summary of Realized Gains and Losses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Net realized investment gains	$ (810)	$ 1,047
Fixed maturity securities
Schedule of Available-for-sale Securities [Line Items]
Gross realized gains	22	338
Gross realized losses	(223)	(296)
Net realized investment gains	(201)	42
Bank loan participations
Schedule of Available-for-sale Securities [Line Items]
Gross realized gains	1,220	1,136
Gross realized losses	(100)	(539)
Net realized investment gains	1,120	597
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Gross realized gains	0	409
Gross realized losses	(15)	0
Changes in fair values of equity securities	(1,710)	0
Net realized investment gains	(1,725)	409
Short-term investments and other
Schedule of Available-for-sale Securities [Line Items]
Gross realized gains	0	0
Gross realized losses	(4)	(1)
Net realized investment gains	$ (4)	$ (1)

Investments - Summary of Privat

Investments - Summary of Private Debt and Equity (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Net Investment Income [Line Items]
Net realized gain (loss) on changes in fair value of impaired bank loans	$ 3	$ 177
Total other invested assets	74,974		$ 70,208
Investment income	1,820	6,062
Renewable energy LLCs
Net Investment Income [Line Items]
Total other invested assets	32,592		32,063
Investment income	1,211	5,594
Renewable energy bridge financing notes
Net Investment Income [Line Items]
Total other invested assets	8,750		7,278
Investment income	$ 297	0
Rate of interest	15.00%
Interest income	$ 297
Limited partnerships
Net Investment Income [Line Items]
Total other invested assets	29,132		26,367
Investment income	226	382
Bank holding companies
Net Investment Income [Line Items]
Total other invested assets	4,500		$ 4,500
Investment income	86	86
Interest income	$ 86	86
Bank Holding Company
Net Investment Income [Line Items]
Rate of interest	7.60%
Interest income	$ 0	1
Investment in private subordinated notes	4,500
Corporate and other | Limited partnerships
Net Investment Income [Line Items]
Carrying values of limited partnerships held	2,900
Investment income (loss)	125	68
Corporate and other | Investment in LLC
Net Investment Income [Line Items]
Cash distributions from LLCs	1,200	1,600
Excess and Surplus Lines | Limited partnerships
Net Investment Income [Line Items]
Carrying values of limited partnerships held	26,300
Investment income (loss)	351	$ 314
Commitment to investment in limited partnership	$ 2,600
Minimum | Corporate and other | Investment in LLC
Net Investment Income [Line Items]
Ownership percentage	2.60%
Maximum | Corporate and other | Investment in LLC
Net Investment Income [Line Items]
Ownership percentage	32.80%

Goodwill and Intangible Asset37

Goodwill and Intangible Assets - Narrative (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 11, 2007
Business Acquisition [Line Items]
Goodwill	$ 181,831	$ 181,831	$ 181,831
James River Group, Inc.
Business Acquisition [Line Items]
Percentage of outstanding shares				100.00%

Goodwill and Intangible Asset38

Goodwill and Intangible Assets - Schedule of Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Acquired Intangible Assets [Line Items]
Identifiable intangibles not subject to amortization	$ 31,364	$ 31,364
Identifiable intangible assets subject to amortization
Gross Carrying Amount	11,611	11,611
Accumulated Amortization	4,790	4,641
Total Intangible Assets, Gross	42,975	42,975
Trademarks
Acquired Intangible Assets [Line Items]
Identifiable intangibles not subject to amortization	22,200	22,200
Insurance licenses and authorities
Acquired Intangible Assets [Line Items]
Identifiable intangibles not subject to amortization	9,164	9,164
Broker relationships
Identifiable intangible assets subject to amortization
Gross Carrying Amount	11,611	11,611
Accumulated Amortization	$ 4,790	$ 4,641
Life (Years)	24 years 7 months 6 days

Earnings Per Share - Narrative

Earnings Per Share - Narrative (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Stock options and restricted share units ("RSU's")
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of securities excluded from the calculations of diluted earnings per share	192,817	97,755

Earnings Per Share - Basic and

Earnings Per Share - Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Net income to shareholders	$ 15,633	$ 18,450
Weighted average common shares outstanding:
Basic (in shares)	29,764,320	29,289,588
Common share equivalents (in shares)	428,983	1,037,835
Diluted (in shares)	30,193,303	30,327,423
Earnings per share:
Basic (in dollars per share)	$ 0.53	$ 0.63
Common share equivalents (in dollars per share)	(0.01)	(0.02)
Diluted (in dollars per share)	$ 0.52	$ 0.61

Reserve for Losses and Loss A41

Reserve for Losses and Loss Adjustment Expenses - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Favorable development on prior year loss reserves
Reserve for losses and loss adjustment expenses	$ 2,610	$ 3,414
Excess and Surplus Lines | Prior accident years | From accident years 2016 and 2014
Favorable development on prior year loss reserves
Reserve for losses and loss adjustment expenses		3,200
Excess and Surplus Lines | Prior accident years | From the 2014-2016 accident years
Favorable development on prior year loss reserves
Reserve for losses and loss adjustment expenses	1,100
Specialty Admitted Insurance | Prior accident years | From accident years 2015, 2014 and prior accident years
Favorable development on prior year loss reserves
Reserve for losses and loss adjustment expenses		42
Specialty Admitted Insurance | Prior accident years | From the 2014-2016 accident years
Favorable development on prior year loss reserves
Reserve for losses and loss adjustment expenses	1,300
Casualty Reinsurance | Prior accident years
Favorable development on prior year loss reserves
Reserve for losses and loss adjustment expenses	$ 176	$ 145

Reserve for Losses and Loss A42

Reserve for Losses and Loss Adjustment Expenses - Reconciliation of Losses and Loss Adjustment Balances (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease) [Abstract]
Reserve for losses and loss adjustment expenses net of reinsurance recoverables at beginning of period	$ 989,825	$ 761,128
Add: Incurred losses and loss adjustment expenses net of reinsurance:
Current year	146,382	108,783
Prior years	(2,610)	(3,414)
Total incurred losses and loss and adjustment expenses	143,772	105,369
Deduct: Loss and loss adjustment expense payments net of reinsurance:
Current year	12,177	3,698
Prior years	83,117	71,018
Total loss and loss adjustment expense payments	95,294	74,716
Reserve for losses and loss adjustment expenses net of reinsurance recoverables at end of period	1,038,303	791,781
Add: Reinsurance recoverables on unpaid losses and loss adjustment expenses at end of period	331,245	188,782	$ 302,524
Reserve for losses and loss adjustment expenses gross of reinsurance recoverables on unpaid losses and loss adjustment expenses at end of period	$ 1,369,548	$ 980,563	$ 1,292,349

Other Comprehensive Income - Su

Other Comprehensive Income - Summary of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Unrealized (losses) gains arising during the period, before U.S. income taxes	$ (19,292)	$ 5,998
U.S. income taxes	544	(1,636)
Unrealized (losses) gains arising during the period, net of U.S. income taxes	(18,748)	4,362
Less reclassification adjustment:
Net realized investment (losses) gains	(201)	450
U.S. income tax expenses	0	(122)
Reclassification adjustment for investment (losses) gains realized in net income	(201)	328
Other comprehensive (loss) income	$ (18,547)	$ 4,034

Contingent Liabilities - Narrat

Contingent Liabilities - Narrative (Details) $ in Millions	Mar. 31, 2018USD ($)
JRG Reinsurance Company, Ltd. | Letter of credit 100 Million
Contingent Liabilities [Line Items]
Letters of credit facility, amount	$ 100
Amount of letters of credit issued	52.2
Assets deposited for securing letters of credit	64.2
JRG Reinsurance Company, Ltd. | Letter of credit 102.5 Million
Contingent Liabilities [Line Items]
Letters of credit facility, amount	102.5
Amount of letters of credit issued	98.6
Assets deposited for securing letters of credit	125.9
JRG Reinsurance Company, Ltd. | Letter of credit 100 Million one
Contingent Liabilities [Line Items]
Letters of credit facility, amount	100
Amount of letters of credit issued	6.9
Assets deposited for securing letters of credit	10
James River Insurance Co
Contingent Liabilities [Line Items]
Total amount deposited in trust accounts	860.6
Third-party Reinsureds | JRG Reinsurance Company, Ltd.
Contingent Liabilities [Line Items]
Total amount deposited in trust accounts	$ 283.1

Segment Information - Narrative

Segment Information - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)segment	Mar. 31, 2017USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment	4
Fee income in Excess and Surplus Lines segment | $	$ 4.8	$ 3.8

Segment Information - Summary o

Segment Information - Summary of Segment Results (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Gross written premiums	$ 298,116	$ 224,179
Net earned premiums	200,942	154,687
Underwriting profit (loss) of insurance segments	14,666	10,735
Net investment income	13,256	16,733
Interest expense	2,522	2,123
Segment revenues	218,344	176,402
Segment goodwill	181,831	181,831	$ 181,831
Segment assets	2,862,010	2,411,325	$ 2,756,695
Reportable segments | Excess and Surplus Lines
Segment Reporting Information [Line Items]
Gross written premiums	167,486	108,995
Net earned premiums	129,971	93,849
Underwriting profit (loss) of insurance segments	11,299	8,800
Net investment income	3,042	3,183
Interest expense	0	0
Segment revenues	137,327	101,090
Segment goodwill	181,831	181,831
Segment assets	909,963	749,617
Reportable segments | Specialty Admitted Insurance
Segment Reporting Information [Line Items]
Gross written premiums	87,401	72,464
Net earned premiums	13,340	16,253
Underwriting profit (loss) of insurance segments	1,623	842
Net investment income	711	636
Interest expense	0	0
Segment revenues	13,955	16,924
Segment goodwill	0	0
Segment assets	495,096	335,806
Reportable segments | Casualty Reinsurance
Segment Reporting Information [Line Items]
Gross written premiums	43,229	42,720
Net earned premiums	57,631	44,585
Underwriting profit (loss) of insurance segments	1,744	1,093
Net investment income	8,017	7,124
Interest expense	0	0
Segment revenues	65,526	52,146
Segment goodwill	0	0
Segment assets	1,368,872	1,211,896
Corporate and Other | Corporate and other
Segment Reporting Information [Line Items]
Gross written premiums	0	0
Net earned premiums	0	0
Underwriting profit (loss) of insurance segments	0	0
Net investment income	1,486	5,790
Interest expense	2,522	2,123
Segment revenues	1,536	6,242
Segment goodwill	0	0
Segment assets	$ 88,079	$ 114,006

Segment Information - Reconcili

Segment Information - Reconciliation of Operating Segments by Individual Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Total underwriting profit of insurance segments	$ 14,666	$ 10,735
Other operating expenses of the Corporate and Other segment	(7,431)	(6,461)
Underwriting profit	7,235	4,274
Net investment income	13,256	16,733
Net realized investment (losses) gains	(810)	1,047
Amortization of intangible assets	(149)	(149)
Other income and expenses	104	200
Interest expense	(2,522)	(2,123)
Income before taxes	17,114	19,982
Reportable segments | Excess and Surplus Lines
Segment Reporting Information [Line Items]
Total underwriting profit of insurance segments	11,299	8,800
Net investment income	3,042	3,183
Interest expense	0	0
Reportable segments | Specialty Admitted Insurance
Segment Reporting Information [Line Items]
Total underwriting profit of insurance segments	1,623	842
Net investment income	711	636
Interest expense	0	0
Reportable segments | Casualty Reinsurance
Segment Reporting Information [Line Items]
Total underwriting profit of insurance segments	1,744	1,093
Net investment income	8,017	7,124
Interest expense	$ 0	$ 0

Other Operating Expenses and 48

Other Operating Expenses and Other Expenses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Other Operating Expenses And Other Expenses [Abstract]
Amortization of policy acquisition costs	$ 30,198	$ 27,638
Other underwriting expenses of the operating segments	17,154	14,794
Other operating expenses of the Corporate and Other segment	7,431	6,461
Total	$ 54,783	$ 48,893

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities	$ 1,129,208,000	$ 1,098,620,000
Impaired bank loan participations held for investment	1,700,000	5,100,000
Unpaid principal on bank loan participations for which external sources were unavailable to determine fair value		807,000
Carrying value of bank loan participations for which external sources were unavailable to determine fair value		$ 0
Market approach | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale securities	$ 4,700,000

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Assets Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	$ 1,129,208	$ 1,098,620
Trading securities:
Fixed maturity securities	3,805	3,808
Short-term investments	26,235	36,804
Fixed maturity securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	1,043,251	1,016,098
State and municipal
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	139,725	144,366
Residential mortgage-backed
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	181,098	158,661
Corporate
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	439,626	413,721
Commercial mortgage and asset-backed
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	190,804	182,611
Obligations of U.S. government corporations and agencies
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	7,775	35,847
U.S. Treasury securities and obligations guaranteed by the U.S. government
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	82,219	78,874
Redeemable preferred stock
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	2,004	2,018
Equity securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	85,957	82,522
Recurring basis
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	1,129,208	1,098,620
Trading securities:
Fixed maturity securities	3,805	3,808
Short-term investments	26,235	36,804
Recurring basis | Fixed maturity securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	1,043,251	1,016,098
Recurring basis | State and municipal
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	139,725	144,366
Recurring basis | Residential mortgage-backed
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	181,098	158,661
Recurring basis | Corporate
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	439,626	413,721
Recurring basis | Commercial mortgage and asset-backed
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	190,804	182,611
Recurring basis | Obligations of U.S. government corporations and agencies
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	7,775	35,847
Recurring basis | U.S. Treasury securities and obligations guaranteed by the U.S. government
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	82,219	78,874
Recurring basis | Redeemable preferred stock
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	2,004	2,018
Recurring basis | Equity securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	85,957	82,522
Recurring basis | Preferred stock
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	67,709	66,281
Recurring basis | Common stock
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	18,248	16,241
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	96,372	93,772
Trading securities:
Fixed maturity securities	0	0
Short-term investments	1,000	1,000
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | Fixed maturity securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	81,640	78,265
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | State and municipal
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	0	0
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | Residential mortgage-backed
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	0	0
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | Corporate
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	0	0
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | Commercial mortgage and asset-backed
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	0	0
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | Obligations of U.S. government corporations and agencies
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	0	0
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | U.S. Treasury securities and obligations guaranteed by the U.S. government
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	81,640	78,265
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | Redeemable preferred stock
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	0	0
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | Equity securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	14,732	15,507
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | Preferred stock
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	0	0
Recurring basis | Quoted Prices in Active Markets for Identical Assets Level 1 | Common stock
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	14,732	15,507
Recurring basis | Significant Other Observable Inputs Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	1,028,156	1,000,168
Trading securities:
Fixed maturity securities	3,805	3,808
Short-term investments	25,235	35,804
Recurring basis | Significant Other Observable Inputs Level 2 | Fixed maturity securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	956,931	933,153
Recurring basis | Significant Other Observable Inputs Level 2 | State and municipal
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	139,725	144,366
Recurring basis | Significant Other Observable Inputs Level 2 | Residential mortgage-backed
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	181,098	158,661
Recurring basis | Significant Other Observable Inputs Level 2 | Corporate
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	439,626	413,721
Recurring basis | Significant Other Observable Inputs Level 2 | Commercial mortgage and asset-backed
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	186,124	177,931
Recurring basis | Significant Other Observable Inputs Level 2 | Obligations of U.S. government corporations and agencies
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	7,775	35,847
Recurring basis | Significant Other Observable Inputs Level 2 | U.S. Treasury securities and obligations guaranteed by the U.S. government
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	579	609
Recurring basis | Significant Other Observable Inputs Level 2 | Redeemable preferred stock
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	2,004	2,018
Recurring basis | Significant Other Observable Inputs Level 2 | Equity securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	71,225	67,015
Recurring basis | Significant Other Observable Inputs Level 2 | Preferred stock
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	67,709	66,281
Recurring basis | Significant Other Observable Inputs Level 2 | Common stock
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	3,516	734
Recurring basis | Significant Unobservable Inputs Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	4,680	4,680
Trading securities:
Fixed maturity securities	0	0
Short-term investments	0	0
Recurring basis | Significant Unobservable Inputs Level 3 | Fixed maturity securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	4,680	4,680
Recurring basis | Significant Unobservable Inputs Level 3 | State and municipal
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	0	0
Recurring basis | Significant Unobservable Inputs Level 3 | Residential mortgage-backed
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	0	0
Recurring basis | Significant Unobservable Inputs Level 3 | Corporate
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	0	0
Recurring basis | Significant Unobservable Inputs Level 3 | Commercial mortgage and asset-backed
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	4,680	4,680
Recurring basis | Significant Unobservable Inputs Level 3 | Obligations of U.S. government corporations and agencies
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	0	0
Recurring basis | Significant Unobservable Inputs Level 3 | U.S. Treasury securities and obligations guaranteed by the U.S. government
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	0	0
Recurring basis | Significant Unobservable Inputs Level 3 | Redeemable preferred stock
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	0	0
Recurring basis | Significant Unobservable Inputs Level 3 | Equity securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	0	0
Recurring basis | Significant Unobservable Inputs Level 3 | Preferred stock
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	0	0
Recurring basis | Significant Unobservable Inputs Level 3 | Common stock
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	$ 0	$ 0

Fair Value Measurements - Sum51

Fair Value Measurements - Summary of Assets Fair Value on a Nonrecurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Bank loan participations held-for-investment	$ 1,700	$ 5,100
Nonrecurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Bank loan participations held-for-investment	1,741	5,111
Nonrecurring basis | Quoted Prices in Active Markets for Identical Assets Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Bank loan participations held-for-investment	0	0
Nonrecurring basis | Significant Other Observable Inputs Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Bank loan participations held-for-investment	0	0
Nonrecurring basis | Significant Unobservable Inputs Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Bank loan participations held-for-investment	$ 1,741	$ 5,111

Fair Value Measurements - Sum52

Fair Value Measurements - Summary of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Available-for-sale:
Fixed maturity securities	$ 1,043,251	$ 1,016,098
Equity securities	85,957	82,522
Trading:
Bank loan participations held-for-investment, at amortized cost, net of allowance	257,426	238,214
Cash and cash equivalents	151,046	163,495	$ 94,224	$ 109,784
Short-term investments	26,235	36,804
Liabilities
Senior debt	98,300	98,300
Junior subordinated debt	104,055	104,055
Carrying Value
Available-for-sale:
Fixed maturity securities	1,043,251	1,016,098
Equity securities	85,957	82,522
Trading:
Fixed maturity securities	3,805	3,808
Bank loan participations held-for-investment, at amortized cost, net of allowance	257,426	238,214
Cash and cash equivalents	151,046	163,495
Short-term investments	26,235	36,804
Other invested assets – notes receivable	13,250	11,778
Liabilities
Senior debt	98,300	98,300
Junior subordinated debt	104,055	104,055
Fair Value
Available-for-sale:
Fixed maturity securities	1,043,251	1,016,098
Equity securities	85,957	82,522
Trading:
Fixed maturity securities	3,805	3,808
Bank loan participations held-for-investment, at amortized cost, net of allowance	257,840	236,532
Cash and cash equivalents	151,046	163,495
Short-term investments	26,235	36,804
Other invested assets – notes receivable	19,056	17,104
Liabilities
Senior debt	98,871	97,884
Junior subordinated debt	$ 118,752	$ 116,569

Capital Stock and Equity Awar53

Capital Stock and Equity Awards - Commons Shares (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares outstanding	29,866,705	29,696,682
Common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common shares issued during period	170,023
Common stock, shares outstanding	29,866,705	29,696,682	29,344,327	29,257,566
Options | Common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common shares issued during period	127,196
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock unit dividend equivalents	$ 99		$ 77
Dividends payable	$ 409	$ 434
RSUs | Common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common shares issued during period	42,827

Capital Stock and Equity Awar54

Capital Stock and Equity Awards - Schedule of Dividends (Details) - USD ($) $ / shares in Units, $ in Millions	Mar. 30, 2018	Feb. 22, 2018	Mar. 31, 2017	Feb. 14, 2017	Mar. 31, 2018	Mar. 31, 2017
Stockholders' Equity Note [Abstract]
Dividend declared per share (in dollars per share)		$ 0.30		$ 0.30	$ 0.30	$ 0.30
Total Amount	$ 9		$ 8.9

Capital Stock and Equity Awar55

Capital Stock and Equity Awards - Equity Incentive Plans (Details)	Mar. 31, 2018shares
2014 LTIP | Non-qualified stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares available for issuance	4,171,150
Number of shares available for grant	1,658,715
2014 Director Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares available for issuance	50,000
Number of shares available for grant	21,663

Capital Stock and Equity Awar56

Capital Stock and Equity Awards - Summary of Option Activity (Details) - Options - $ / shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Shares
Beginning of period (in shares)	1,479,236	2,234,699
Granted (in shares)	0	195,509
Exercised (in shares)	(142,129)	(97,211)
Forfeited (in shares)	0	(50,062)
End of period (in shares)	1,337,107	2,282,935
Exercisable, end of period (in shares)	983,508	1,334,756
Weighted- Average Exercise Price
Beginning of period (in dollars per share)	$ 27.81	$ 22.84
Granted (in dollars per share)	0	42.17
Exercised (in dollars per share)	20.14	17.23
Forfeited (in dollars per share)	0	27.97
End of period (in dollars per share)	28.63	24.62
Exercisable, end of period (in dollars per share)	$ 26.06	$ 20.47
Vesting period (in years)	7 years
Minimum
Weighted- Average Exercise Price
Vesting period (in years)	3 years
Maximum
Weighted- Average Exercise Price
Vesting period (in years)	4 years

Capital Stock and Equity Awar57

Capital Stock and Equity Awards - Summary of RSU Activity (Details) - RSUs - $ / shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Shares
Unvested, beginning of period (in shares)	178,882	196,800
Granted (in shares)	214,907	117,879
Vested (in shares)	(62,714)	(37,485)
Forfeited (in shares)	0	(19,743)
Unvested, end of period (in shares)	331,075	257,451
Shares
Unvested, beginning of period (in dollars per share)	$ 37.93	$ 24.38
Granted (in dollars per share)	39.81	42.17
Vested (in dollars per share)	40.90	32.07
Forfeited (in dollars per share)	0	24.06
Unvested, end of period (in dollars per share)	$ 38.59	$ 31.43
Vesting period (in years)	3 years
Non-employee directors
Shares
Vesting period (in years)	1 year
Minimum
Shares
Vesting period (in years)	1 year
Maximum
Shares
Vesting period (in years)	5 years

Capital Stock and Equity Awar58

Capital Stock and Equity Awards - Summary of Share Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Stockholders' Equity Note [Abstract]
Share based compensation expense	$ 1,455	$ 1,794
U.S. tax benefit on share based compensation expense	$ 173	$ 469

Capital Stock and Equity Awar59

Capital Stock and Equity Awards - Compensation Expense (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)
Equity [Abstract]
Unrecognized share based compensation expense	$ 14
Weighted-average period of unrecognized share based compensation expense (in years)	2 years 3 months 18 days
Weighted-average remaining contractual life of options outstanding (in years)	4 years 4 months 24 days
Weighted-average remaining contractual life of options exercisable (in years)	4 years

Subsequent Events (Details)

Subsequent Events (Details) - Subsequent event - $ / shares	Jun. 29, 2018	Jun. 11, 2018	May 01, 2018
Subsequent Event [Line Items]
Dividends payable, date declared			May 1, 2018
Cash dividend declared (in dollars per share)			$ 0.30
Dividends payable, date to be paid	Jun. 29, 2018
Dividend payable, record date		Jun. 11, 2018