Investments at fair value Investments at fair value - Schedule of Debt and Equity Securities (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale, Amortized Cost [Abstract]
Available-for-sale Debt Securities, Amortized Cost Basis	$ 230,408	$ 147,386
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	1,643	250
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(366)	(825)
Available-for-sale Securities [Abstract]
Debt Securities	231,685
Investments at fair value	231,685	146,811
Interest and Dividend Income, Securities, Operating, Available-for-sale	300
Beneficial interests in securitization trusts
Debt Securities, Available-for-sale, Amortized Cost [Abstract]
Available-for-sale Securities, Amortized Cost Basis	57,954	22,086
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Available-for-sale Securities [Abstract]
Available-for-sale Securities	57,954	22,086
Accumulated Net Investment Gain (Loss) Attributable to Noncontrolling Interest
Debt Securities, Available-for-sale, Amortized Cost [Abstract]
Available-for-sale Securities, Amortized Cost Basis	288,362	169,472
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		825
Available-for-sale Securities [Abstract]
Available-for-sale Securities	289,639	168,897
Debt securities due April 2058
Debt Securities, Available-for-sale, Amortized Cost [Abstract]
Available-for-sale Debt Securities, Amortized Cost Basis	6,855	7,896
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(9)	(315)
Available-for-sale Securities [Abstract]
Investments at fair value	6,846	7,581
Debt securities due February 2057
Debt Securities, Available-for-sale, Amortized Cost [Abstract]
Available-for-sale Debt Securities, Amortized Cost Basis	7,324	11,813
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(1)	(203)
Available-for-sale Securities [Abstract]
Investments at fair value	7,323	11,610
Debt securities due September 2059
Debt Securities, Available-for-sale, Amortized Cost [Abstract]
Available-for-sale Debt Securities, Amortized Cost Basis	37,843
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(356)
Available-for-sale Securities [Abstract]
Investments at fair value	37,487
Debt securities due June 2058
Debt Securities, Available-for-sale, Amortized Cost [Abstract]
Available-for-sale Debt Securities, Amortized Cost Basis		18,702
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax		(3)
Available-for-sale Securities [Abstract]
Investments at fair value		18,699
Debt securities due August 2058
Debt Securities, Available-for-sale, Amortized Cost [Abstract]
Available-for-sale Debt Securities, Amortized Cost Basis		16,143
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax		(297)
Available-for-sale Securities [Abstract]
Investments at fair value		15,846
Debt securities due November 2058
Debt Securities, Available-for-sale, Amortized Cost [Abstract]
Available-for-sale Debt Securities, Amortized Cost Basis		45,680
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax		(7)
Available-for-sale Securities [Abstract]
Investments at fair value		45,673
Debt securities basis
Debt Securities, Available-for-sale, Amortized Cost [Abstract]
Available-for-sale Securities, Amortized Cost Basis	52,022	100,234
Debt securities carrying value
Available-for-sale Securities [Abstract]
Available-for-sale Securities	51,656	$ 99,409
Debt Securities Gross Unrealized Gain (Losses)
Available-for-sale Securities, Gross Unrealized Gain (Loss) [Abstract]
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 366

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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-Publisher FASB
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