Investments (Realized and unrealized gains (losses)) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fixed maturities, short-term and other investments
Net realized gains on investments	$ 9,220	$ 4,397	$ 2,724	$ (584)	$ (2,928)	$ (1,187)	$ 2,244	$ 4,169	$ 15,757	$ 2,298	$ 14,917
Change in net unrealized gains (losses) on managed investments (a)	$ (67,460)	$ 5,459	$ 31,428	$ 47,444	$ (34,862)	$ 3,916	$ (34,676)	$ 33,227	16,871	(32,395)	(2,842)
Total net realized gains and change in net unrealized gains (losses) gains on investments									32,628	(30,097)	12,075
Managed investments
Fixed maturities, short-term and other investments
Gross realized gains									22,491	15,678	20,201
Gross realized (losses)									(7,811)	(13,980)	(8,041)
Net realized gains on investments									14,680	1,698	12,160
Change in net unrealized gains (losses) on managed investments (a)									14,106	(32,007)	(1,030)
Total net realized gains and change in net unrealized gains (losses) gains on investments									28,786	(30,309)	11,130
Non-managed investments
Fixed maturities, short-term and other investments
Gross realized gains									1,086	611	2,757
Gross realized (losses)									(9)	(11)	0
Net realized gains on investments									1,077	600	2,757
Change in net unrealized gains (losses) on managed investments (a)									2,765	(388)	(1,812)
Total net realized gains and change in net unrealized gains (losses) gains on investments									$ 3,842	$ 212	$ 945