Fair Value Measurements - Long-term Debt (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Carrying Value	$ 1,008.3	$ 659.3
Senior Loans [Member]
Debt Instrument [Line Items]
Carrying Value	460.1	484.2
Junior Loans [Member]
Debt Instrument [Line Items]
Carrying Value	48.9	54.3
Equipment Notes, Series A [Member]
Debt Instrument [Line Items]
Carrying Value	394.8	95.8
Equipment Notes, Series B [Member]
Debt Instrument [Line Items]
Carrying Value	104.5	25.0
Estimated Fair Value [Member]
Debt Instrument [Line Items]
Estimated Fair Value	1,036.7	652.4
Estimated Fair Value [Member] | Level 3 [Member] | Senior Loans [Member]
Debt Instrument [Line Items]
Estimated Fair Value	477.4	477.8
Estimated Fair Value [Member] | Level 3 [Member] | Junior Loans [Member]
Debt Instrument [Line Items]
Estimated Fair Value	50.5	54.6
Estimated Fair Value [Member] | Level 2 [Member] | Equipment Notes, Series A [Member]
Debt Instrument [Line Items]
Estimated Fair Value	402.7	94.8
Estimated Fair Value [Member] | Level 2 [Member] | Equipment Notes, Series B [Member]
Debt Instrument [Line Items]
Estimated Fair Value	$ 106.1	$ 25.2