Commitments and Contingencies (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Acquisition of mortgage loans
Loss Contingencies [Line Items]
Amount of purchase commitment	$ 171.5	$ 221.0
Purchase of limited partnerships and private placement investments
Loss Contingencies [Line Items]
Amount of purchase commitment	$ 612.4	$ 330.4