Related Party Transactions (Narrative) (Details) $ in Thousands	1 Months Ended				3 Months Ended		9 Months Ended		12 Months Ended
	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jun. 30, 2015 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) policy	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)	Apr. 01, 2016 USD ($)	Oct. 31, 2013 USD ($)
Related Party Transaction [Line Items]
Other long-term investments			$ 379,237		$ 327,010		$ 327,010		$ 379,237
Net investment income					103,743	$ 102,215	287,814	$ 307,121
Contributed capital							205,000	0
Prudential Insurance
Related Party Transaction [Line Items]
Contributed capital	$ 200,000	$ 5,000					205,000		0
Dividend			200,000	$ 230,000			2,600,000
Prudential Insurance and Prudential FInancial
Related Party Transaction [Line Items]
Life Insurance, Corporate or Bank Owned, amount			2,873,000		3,317,000		3,317,000		2,873,000
Fees related to Life Insurance, Corporate or Bank Owned, amount					10,000	13,000	31,000	34,000
Maximum amount of mortality risk											$ 3,500
Prudential Insurance
Related Party Transaction [Line Items]
Stock option program plan expense					300	300	900	900
Deferred compensation program expense					2,000	1,000	6,000	5,000
Pension plan expense					6,000	5,000	17,000	16,000
Welfare plan expense					7,000	7,000	$ 21,000	19,000
Defined contribution plan, employer matching contribution, percent (up to)							4.00%
Defined contribution plan, cost recognized					2,000	2,000	$ 7,000	6,000
Number of Corporate Owned Life Insurance policies sold | policy							5
Prudential Financial
Related Party Transaction [Line Items]
Number of Corporate Owned Life Insurance policies sold | policy							1
Affiliated Entity
Related Party Transaction [Line Items]
Accrued interested receivable related to long-tern notes receivable			1,000		1,000		$ 1,000		1,000
Revenues related to long-term notes receivable					1,000	2,000	4,000	6,000
Line of credit facility, maximum borrowing capacity					2,200,000		2,200,000
Prepaid debt										$ 125,000
Interest expense related to loans payable					0	13,000	13,000	39,000
Affiliated Entity | PAD
Related Party Transaction [Line Items]
Commissions and certain other fees					182,000	177,000	546,000	592,000
Affiliated Entity | ASTISI and Prudential Investments
Related Party Transaction [Line Items]
Revenue administrative sharing agreement					76,000	81,000	218,000	274,000
Affiliated Entity | Prudential Investments
Related Party Transaction [Line Items]
Revenue administrative sharing agreement					3,000	3,000	10,000	10,000
Affiliated Entity | PGIM
Related Party Transaction [Line Items]
Net investment income					3,000	4,000	12,000	$ 13,000
Prudential Financial Joint Ventures
Related Party Transaction [Line Items]
Other long-term investments			$ 146,000		96,000		96,000		146,000
Net investment income					$ 3,000	$ (5,000)	$ (100)		$ 0