Investment in Securities, Securities in Continuous Unrealized Loss Position (Details)
$ in Thousands
 12 Months Ended
Dec. 31, 2016
USD ($)
Security
Dec. 31, 2015
USD ($)
Security
Dec. 31, 2014
USD ($)
Available-for-sale securities, continuous unrealized loss position, estimated fair value [Abstract]      
Less than 12 months $ 274,219 $ 240,407  
12 months or longer 784 0  
Total 275,003 240,407  
Available-for-sale securities, continuous unrealized loss position, gross unrealized loss [Abstract]      
Less than 12 months (2,002) (1,460)  
12 months or longer (3) 0  
Total $ (2,005) $ (1,460)  
Available-for-sale, securities in unrealized loss positions, number of securities [Abstract]      
Less than 12 months | Security 54 29  
12 months or longer | Security 1 0  
Total | Security 55 29  
Minimum percentage of gross unrealized investment losses as cost 20.00%    
Minimum unrealized loss of investment as indicator of other-than-temporary impairment $ 100    
Estimated Fair Value 1,151,643 $ 1,133,645  
Impairment losses from other-than-temporary impairments 1,434 5,212 $ 1,170
Obligations of Government-sponsored Enterprises [Member]      
Available-for-sale securities, continuous unrealized loss position, estimated fair value [Abstract]      
Less than 12 months 9,483 18,989  
12 months or longer 0 0  
Total 9,483 18,989  
Available-for-sale securities, continuous unrealized loss position, gross unrealized loss [Abstract]      
Less than 12 months (15) (26)  
12 months or longer 0 0  
Total $ (15) $ (26)  
Available-for-sale, securities in unrealized loss positions, number of securities [Abstract]      
Less than 12 months | Security 1 1  
12 months or longer | Security 0 0  
Total | Security 1 1  
Estimated Fair Value $ 41,514 $ 116,240  
U.S. Treasury Securities and Obligations of U.S. Government Instrumentalities [Member]      
Available-for-sale securities, continuous unrealized loss position, estimated fair value [Abstract]      
Less than 12 months 12,937 130,996  
12 months or longer 0 0  
Total 12,937 130,996  
Available-for-sale securities, continuous unrealized loss position, gross unrealized loss [Abstract]      
Less than 12 months (9) (286)  
12 months or longer 0 0  
Total $ (9) $ (286)  
Available-for-sale, securities in unrealized loss positions, number of securities [Abstract]      
Less than 12 months | Security 1 5  
12 months or longer | Security 0 0  
Total | Security 1 5  
Estimated Fair Value $ 85,800 $ 163,270  
Obligations of the Commonwealth of Puerto Rico and its instrumentalities [Member]      
Available-for-sale securities, continuous unrealized loss position, estimated fair value [Abstract]      
Less than 12 months 7,758    
12 months or longer 0    
Total 7,758    
Available-for-sale securities, continuous unrealized loss position, gross unrealized loss [Abstract]      
Less than 12 months (68)    
12 months or longer 0    
Total $ (68)    
Available-for-sale, securities in unrealized loss positions, number of securities [Abstract]      
Less than 12 months | Security 5    
12 months or longer | Security 0    
Total | Security 5    
Estimated Fair Value $ 20,051 25,619  
Municipal Securities [Member]      
Available-for-sale securities, continuous unrealized loss position, estimated fair value [Abstract]      
Less than 12 months 84,252 43,937  
12 months or longer 0 0  
Total 84,252 43,937  
Available-for-sale securities, continuous unrealized loss position, gross unrealized loss [Abstract]      
Less than 12 months (559) (197)  
12 months or longer 0 0  
Total $ (559) $ (197)  
Available-for-sale, securities in unrealized loss positions, number of securities [Abstract]      
Less than 12 months | Security 13 11  
12 months or longer | Security 0 0  
Total | Security 13 11  
Estimated Fair Value $ 683,803 $ 647,446  
Corporate Bonds [Member]      
Available-for-sale securities, continuous unrealized loss position, estimated fair value [Abstract]      
Less than 12 months 105,054 35,718  
12 months or longer 0 0  
Total 105,054 35,718  
Available-for-sale securities, continuous unrealized loss position, gross unrealized loss [Abstract]      
Less than 12 months (661) (572)  
12 months or longer 0 0  
Total $ (661) $ (572)  
Available-for-sale, securities in unrealized loss positions, number of securities [Abstract]      
Less than 12 months | Security 22 9  
12 months or longer | Security 0 0  
Total | Security 22 9  
Estimated Fair Value $ 274,872 $ 157,408  
Collateralized Mortgage Obligations [Member]      
Available-for-sale securities, continuous unrealized loss position, estimated fair value [Abstract]      
Less than 12 months 32,120 1,448  
12 months or longer 784 0  
Total 32,904 1,448  
Available-for-sale securities, continuous unrealized loss position, gross unrealized loss [Abstract]      
Less than 12 months (239) (6)  
12 months or longer (3) 0  
Total $ (242) $ (6)  
Available-for-sale, securities in unrealized loss positions, number of securities [Abstract]      
Less than 12 months | Security 8 1  
12 months or longer | Security 1 0  
Total | Security 9 1  
Estimated Fair Value $ 44,885 $ 22,725  
Fixed Maturities Securities [Member]      
Available-for-sale securities, continuous unrealized loss position, estimated fair value [Abstract]      
Less than 12 months 251,604 231,088  
12 months or longer 784 0  
Total 252,388 231,088  
Available-for-sale securities, continuous unrealized loss position, gross unrealized loss [Abstract]      
Less than 12 months (1,551) (1,087)  
12 months or longer (3) 0  
Total $ (1,554) $ (1,087)  
Available-for-sale, securities in unrealized loss positions, number of securities [Abstract]      
Less than 12 months | Security 50 27  
12 months or longer | Security 1 0  
Total | Security 51 27  
Impairment losses from other-than-temporary impairments $ 0 $ 4,267 1,170
Mutual Funds [Member]      
Available-for-sale securities, continuous unrealized loss position, estimated fair value [Abstract]      
Less than 12 months 22,615 9,319  
12 months or longer 0 0  
Total 22,615 9,319  
Available-for-sale securities, continuous unrealized loss position, gross unrealized loss [Abstract]      
Less than 12 months (451) (373)  
12 months or longer 0 0  
Total $ (451) $ (373)  
Available-for-sale, securities in unrealized loss positions, number of securities [Abstract]      
Less than 12 months | Security 4 2  
12 months or longer | Security 0 0  
Total | Security 4 2  
Estimated Fair Value $ 11,582 $ 13,189 0
Impairment losses from other-than-temporary impairments 1,434 945 0
Escrow Bonds [Member]      
Available-for-sale, securities in unrealized loss positions, number of securities [Abstract]      
Estimated Fair Value 7,758    
Gross unrealized gains (losses) (68)    
Cofina Bonds [Member]      
Available-for-sale, securities in unrealized loss positions, number of securities [Abstract]      
Estimated Fair Value 12,293    
Impairment losses from other-than-temporary impairments 0 $ 4,267 $ 1,170
Gross unrealized gains (losses) $ 2,189