Income Taxes (Details) - USD ($)
$ in Thousands
 4 Months Ended 12 Months Ended
Oct. 31, 2014
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Income Tax Examination [Line Items]        
Limit on income tax credit for regular income tax in excess of alternative minimum income tax paid   25.00%    
Federal income tax   $ 733 $ 574 $ 451
Total outside basis difference   26,000 59,000  
One-time charge to operations   6,300    
Components of income tax expense (benefit) [Abstract]        
Current income tax expense   1,981 10,169 22,551
Deferred income tax benefit   (8,326) (5,070) (21,806)
Total income tax (benefit) expense   (6,345) 5,099 745
Income tax (benefit) expense reconciliation [Abstract]        
Income before taxes   $ 11,086 $ 57,131 $ 66,051
Statutory tax rate   39.00% 39.00% 39.00%
Income tax expense at statutory rate   $ 4,324 $ 22,281 $ 25,760
Increase (decrease) in taxes resulting from [Abstract]        
Exempt interest income, net   (5,158) (6,041) (7,139)
Effect of taxing life insurance operations as a qualified domestic life insurance company instead of as a regular corporation   (5,033) (4,936) (5,572)
Effect of taxing capital gains at a preferential rate   (3,799) (7,432) (14,248)
Dividends received deduction   0 270 173
Adjustment to deferred tax assets and liabilities for changes in effective tax rates   1,669 (1,576) 5,466
Other adjustments to deferred tax assets and liabilities   2,852 (58) (707)
Effect of extraordinary dividend distribution from the Association - reported net of taxes in other income   (151) (875) 0
Tax credit benefit   (709) (537) (1,482)
Tax returns to provision true up   (181) (1,084) 0
Effect of reassessment of unused credits for alternative minimum taxes paid   0 0 (6,486)
Subtotal   (10,510) (22,269) (29,995)
Other permanent disallowances, net [Abstract]        
Disallowed resolution agreements expense   0 1,716 0
Disallowance of expenses related to exempt interest income   58 0 46
Disallowed dividend received deduction   0 3,598 4,815
Disallowed interest expense   8 12 21
Other   0 61 282
Total other permanent differences   66 5,387 5,164
Other adjustments   (225) (300) (184)
Total income tax (benefit) expense   (6,345) 5,099 $ 745
Deferred tax assets [Abstract]        
Allowance for doubtful receivables   10,070 13,434  
Liability for pension benefits   10,624 21,416  
Employee benefits plan   1,580 3,177  
Postretirement benefits   772 1,252  
Deferred compensation   2,041 1,818  
Accumulated depreciation   1,137 1,240  
Impairment loss on investments   2,035 1,749  
Contingency reserves   0 30  
Share-based compensation   4,393 4,875  
Alternative minimum income tax credit   1,991 2,066  
Purchased tax credits   6,062 931  
Net operating loss   33,081 12,721  
Difference in tax basis of investments portfolio   3,049 6,843  
Accrued liabilities   2,133 2,402  
Other   772 591  
Gross deferred tax assets   79,740 74,545  
Less: valuation allowance   (8,016) (7,839)  
Deferred tax assets   71,724 66,706  
Deferred tax liabilities [Abstract]        
Deferred policy acquisition costs   (6,621) (3,673)  
Catastrophe loss reserve   (8,020) (7,664)  
Unrealized gain on securities available for sale   (15,804) (15,021)  
Unamortized debt issue costs   (152) (29)  
Intangible asset   (2,195) (3,013)  
Accumulated depreciation   (14) (15)  
Gross deferred tax liabilities   (32,806) (29,415)  
Net deferred tax asset   38,918 37,291  
Deferred tax assets, net   57,768 52,361  
Deferred tax liabilities, net   $ 18,850 15,070  
Puerto Rico [Member]        
Income Tax Examination [Line Items]        
Percentage of premium tax on policies underwritten   5.00%    
Income tax prepayments at reduced rate 12.00%      
Components of income tax expense (benefit) [Abstract]        
Total income tax (benefit) expense     2,524  
Other permanent disallowances, net [Abstract]        
Total income tax (benefit) expense     $ 2,524  
Deferred tax liabilities [Abstract]        
Operating loss carryforwards   $ 75,000    
Puerto Rico [Member] | Minimum [Member]        
Income Tax Examination [Line Items]        
Changes to the corporate tax   15.00%    
Puerto Rico [Member] | Maximum [Member]        
Income Tax Examination [Line Items]        
Changes to the corporate tax   20.00%