Fair Value Measurements (Assets and Liabilities Measured at Fair Value on a Recurring Basis Using Level 3 Inputs) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ (13,004)	$ 1,719
Total unrealized gains (losses)
Purchases		(13,444)
Settlements		(7,500)
Ending balance		(13,004)
Included in net investment income
Total unrealized gains (losses)
Included in income		(118)
Included in other income
Total unrealized gains (losses)
Included in income		6,339
Other assets and (liabilities)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	(13,004)	(5,899)
Total unrealized gains (losses)
Purchases	(354)	(13,444)
Settlements	(5,937)	0
Ending balance	(2,952)	(13,004)
Other assets and (liabilities) | Included in net investment income
Total unrealized gains (losses)
Included in income		0
Other assets and (liabilities) | Included in other income
Total unrealized gains (losses)
Included in income	3,761	6,339
Fixed maturity investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 0	7,618
Total unrealized gains (losses)
Purchases		0
Settlements		(7,500)
Ending balance		0
Fixed maturity investments | Included in net investment income
Total unrealized gains (losses)
Included in income		(118)
Fixed maturity investments | Included in other income
Total unrealized gains (losses)
Included in income		$ 0