Other income and operating expenses - Paycheck Protection Program (Details) $ in Thousands		1 Months Ended	3 Months Ended	12 Months Ended
	Apr. 28, 2020	Apr. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) item	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Paycheck Protection Program (PPP)
Number of non-bank SBA lenders | item				14
Origination costs				$ 19,815	$ 10,168	$ 7,752
Deferred servicing and forgiveness fees				10,700
PPP Loans
Paycheck Protection Program (PPP)
Loans funded		$ 114,700		2,700,000
PPP processing fees		$ 5,200
Deferred servicing and forgiveness fees				10,700
Lender Service Provider Agreement
Paycheck Protection Program (PPP)
Fees received as a percentage of total fees received by third party from SBA	50.00%
Lender Service Provider Agreement | PPP Loans
Paycheck Protection Program (PPP)
Amount of PPP loans underwritten and sold to third party			$ 2,500,000
Cash proceeds from origination and servicing fees			43,300
Origination fee and fee income			27,800
Deferred servicing and forgiveness fees			$ 15,500	$ 10,700