Commitments and Contingencies - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Loss Contingencies [Line Items]
Rent expense	$ 4.1	$ 4.1	$ 3.8
Loan Purchase Commitments [Member]
Loss Contingencies [Line Items]
Long-term Purchase Commitment, Amount	602.0	221.0
Investment Purchase Commitment [Member]
Loss Contingencies [Line Items]
Long-term Purchase Commitment, Amount	$ 455.9	$ 330.4