Bank segment - Available-for-sale securities, narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Bank Subsidiary [Abstract]
Proceeds from sale of available-for-sale investment securities	$ 0	$ 19,800,000	$ 169,157,000	$ 19,810,000
Gross realized gains on available-for-sale securities	0	700,000	9,300,000	700,000
Gross realized losses on available-for-sale securities	0	0	0	0
Tax expense on realized gains	$ 0	$ 200,000	$ 2,500,000	$ 200,000