Other income and operating expenses - Income and Expenses Related to Activities (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended								12 Months Ended
	Apr. 30, 2020	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Other income
LSP origination fees										$ 40,836	$ 5,860	$ 4,590
Interest income										258,636	229,916	169,499
Interest and Fee Income										243,648	218,267	159,957
Other operating expenses
Direct operating expenses										19,815	10,168	7,752
R&D reserve										(4,133)	345	163
Interest expense										175,481	151,880	109,238
Total other operating expenses										54,369	33,162	28,747
Net income (loss)		$ 27,559	$ 35,363	$ 34,663	$ (51,516)	$ 20,934	$ 12,427	$ 11,245	$ 30,450	46,069	$ 75,056	$ 61,457
PPP Loans
Other income
PPP processing fees	$ 5,200
Interest and Fee Income										38,498
Other operating expenses
Total other operating expenses										15,079
Net income (loss)										23,419
PPP Loans | Other Income
Other income
LSP origination fees										27,768
PPP processing fees										5,162
Other operating expenses
R&D reserve										3,305
PPP Loans | Servicing income
Other income
LSP fee income										4,829
PPP Loans | Interest income
Other income
Interest income										739
PPP Loans | Other operating expenses
Other operating expenses
Direct operating expenses										9,600
PPP Loans | Interest expense
Other operating expenses
Interest expense										$ 2,174