Variable interest entities ("VIEs") (Details)	Dec. 31, 2023 USD ($) company	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Variable Interest Entity [Line Items]
Number of special purpose acquisition companies | company	2
Cash and cash equivalents	$ 28,835,000	$ 112,433,000	$ 213,759,000
Restricted cash	0	25,534,000	$ 127,765,000
Other assets	190,764,000	184,443,000
Total assets	2,874,816,000	2,714,392,000
Total liabilities	2,085,577,000	1,893,971,000
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Cash and cash equivalents	94,000	1,694,000
Restricted cash	0	25,535,000
Other assets	387,000	318,000
Total assets	481,000	27,547,000
Other Liabilities	171,000	828,000
Total liabilities	$ 171,000	$ 828,000