Investments (Securities Lending and Repurchase Agreement) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total cash collateral for loaned securities(1)	$ 7,835	$ 23,350
Overnight & Continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total cash collateral for loaned securities(1)	7,835	23,350
Up to 30 Days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total cash collateral for loaned securities(1)	0	0
Foreign government bonds
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total cash collateral for loaned securities(1)	83	10,712
Foreign government bonds | Overnight & Continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total cash collateral for loaned securities(1)	83	10,712
Foreign government bonds | Up to 30 Days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total cash collateral for loaned securities(1)	0	0
All other U.S. public corporate securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total cash collateral for loaned securities(1)	7,752	12,638
All other U.S. public corporate securities | Overnight & Continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total cash collateral for loaned securities(1)	7,752	12,638
All other U.S. public corporate securities | Up to 30 Days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total cash collateral for loaned securities(1)	0	0
All other foreign public corporate securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total cash collateral for loaned securities(1)	0	0
All other foreign public corporate securities | Overnight & Continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total cash collateral for loaned securities(1)	0	0
All other foreign public corporate securities | Up to 30 Days
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Total cash collateral for loaned securities(1)	$ 0	$ 0