Asset-Backed Financing - Quarterly Transfer Information (Details) - Secured Debt - Consolidated VIEs - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jul. 01, 2018	Apr. 01, 2018	Jun. 30, 2019	Jul. 01, 2018
Asset-backed U.S. commercial paper conduit facilities | U.S. Line of Credit
Variable Interest Entity
Transfers	$ 0	$ 0	$ 59,100	$ 32,900	$ 0	$ 92,000
Proceeds	0	0	53,300	29,300	0	82,600
Asset-backed Canadian commercial paper conduit facility | Foreign Line of Credit
Variable Interest Entity
Transfers	28,200	0	38,900	7,600	28,200	46,500
Proceeds	$ 23,400	$ 0	$ 32,200	$ 6,200	$ 23,400	$ 38,400