Financial Derivatives (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Written credit derivative spread threshold	20.00%	20.00%
Credit Default Swap, Selling Protection [Member]
Derivative [Line Items]
Credit risk derivative in excess of threshold, at fair value, net	$ (0.2)	$ (1.0)
Total net up-front payments received	$ (2.0)	$ (2.0)
Minimum
Derivative [Line Items]
Spread on written credit derivatives	0.426%	0.218%
Upfront points on written credit derivative in excess of threshold	36.9	56.3
Maximum
Derivative [Line Items]
Spread on written credit derivatives	8.151%	19.56%
Upfront points on written credit derivative in excess of threshold	75.2	74.7