Fair Value Measurements (Assets and Liabilities Measured at Fair Value on a Recurring Basis Using Level 3 Inputs) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of the period	$ (2,680)	$ 83,347	$ 1,719	$ 6,726
Total unrealized gains (losses)
Included in net investment income		(61)	(118)	(385)
Included in other income		(78)		(426)
Total realized gains (losses)
Included in other income	795	1,827	4,587	4,655
Total foreign exchange gains (losses)		7		7
Purchases	(10,127)	(498)	(10,700)	81,467
Settlements	0	0	(7,500)	(7,500)
Balance at end of the period	(12,012)	84,544	(12,012)	84,544
Net investment income
Total realized gains (losses)
Change in unrealized gains for the period included in earnings for assets held at the end of the period		(61)		(203)
Other income (loss)
Total realized gains (losses)
Change in unrealized gains for the period included in earnings for assets held at the end of the period		(78)		(426)
Fixed maturity investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of the period	0	7,660	7,618	15,660
Total unrealized gains (losses)
Included in net investment income		(65)	(118)	(565)
Included in other income		0		0
Total realized gains (losses)
Included in other income	0	0	0	0
Total foreign exchange gains (losses)		0		0
Purchases	0	0	0	0
Settlements	0	0	(7,500)	(7,500)
Balance at end of the period	0	7,595	0	7,595
Fixed maturity investments | Net investment income
Total realized gains (losses)
Change in unrealized gains for the period included in earnings for assets held at the end of the period		(65)		(383)
Fixed maturity investments | Other income (loss)
Total realized gains (losses)
Change in unrealized gains for the period included in earnings for assets held at the end of the period		0		0
Other assets and (liabilities)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of the period	(2,680)	75,687	(5,899)	(8,934)
Total unrealized gains (losses)
Included in net investment income		4	0	180
Included in other income		(78)		(426)
Total realized gains (losses)
Included in other income	795	1,827	4,587	4,655
Total foreign exchange gains (losses)		7		7
Purchases	(10,127)	(498)	(10,700)	81,467
Settlements	0	0	0	0
Balance at end of the period	$ (12,012)	76,949	$ (12,012)	76,949
Other assets and (liabilities) | Net investment income
Total realized gains (losses)
Change in unrealized gains for the period included in earnings for assets held at the end of the period		4		180
Other assets and (liabilities) | Other income (loss)
Total realized gains (losses)
Change in unrealized gains for the period included in earnings for assets held at the end of the period		$ (78)		$ (426)