Loans Held-for-Investment - Troubled Debt Restructurings, Narrative (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) loan	Dec. 31, 2018 USD ($) loan	Dec. 31, 2017 USD ($) loan
Receivables [Abstract]
Loans modified in the preceding 12 months that subsequently defaulted | loan	0	0	1
Modifications subsequent to default (less than)	$ 0	$ 0	$ 1,000,000
Increase (decrease) in allowance associated with TDRs at subsequent default	$ 0