Finance Receivable Sale Agreements - Narrative (Details)	3 Months Ended
	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Nov. 02, 2018 USD ($) multiplier	Nov. 03, 2017 USD ($)	Nov. 02, 2017 USD ($)	Dec. 31, 2016 USD ($)
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale [Line Items]
Purchase of finance receivables	$ 127,710,000	$ 0
Consumer Loan | Master Transfer Agreement
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale [Line Items]
Transfer of financial assets, accounted for as sales, maximum amount eligible to be sold				$ 357,100,000		$ 292,200,000
Consumer Loan | MPSA
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale [Line Items]
Transfer of financial assets, accounted for as sales, maximum amount eligible to be sold				$ 1,500,000,000	$ 375,000,000.0	$ 375,000,000.0
Receivable purchase agreement, remaining unused capacity	1,100,000,000
Commitment of purchaser, current availability financing, principal balances of finance receivables (up to)			$ 1,250,000,000
Transfer of financial assets accounted for as sales, amount derecognized	65,300,000	125,600,000
Consumer Loan | Master Transfer Agreement 2017
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale [Line Items]
Receivable purchase agreement, remaining unused capacity	396,200,000		$ 454,500,000
Purchase commitment multiplier | multiplier			3
Transfer of financial assets accounted for as sales, amount derecognized	58,300,000	85,500,000
Consumer Loan | Master Purchase And Sale Agreement And 2017 Master Transfer Agreement
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale [Line Items]
Gain on loan sales	$ 19,200,000	$ 9,900,000