Investment securities - Schedule of Gross Unrealized Losses (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Abstract]
Debt securities, available-for-sale, unrealized loss, less than 12 months, fair value	$ 63,074	$ 87,858
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months, accumulated loss	(394)	(844)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, fair value	175,730	369,343
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(1,497)	(14,247)
Debt securities, available-for-sale, continuous unrealized loss position, fair value	238,804	457,201
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(1,891)	(15,091)
U.S. government agency securities
Debt Securities, Available-for-sale [Abstract]
Debt securities, available-for-sale, unrealized loss, less than 12 months, fair value		0
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months, accumulated loss		0
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, fair value		989
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss		(11)
Debt securities, available-for-sale, continuous unrealized loss position, fair value		989
Debt securities, available-for-sale, unrealized loss position, accumulated loss		(11)
Mortgage-backed securities - residential
Debt Securities, Available-for-sale [Abstract]
Debt securities, available-for-sale, unrealized loss, less than 12 months, fair value	47,641	60,347
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months, accumulated loss	(164)	(478)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, fair value	175,730	335,769
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(1,497)	(12,787)
Debt securities, available-for-sale, continuous unrealized loss position, fair value	223,371	396,116
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(1,661)	(13,265)
Municipals, tax exempt
Debt Securities, Available-for-sale [Abstract]
Debt securities, available-for-sale, unrealized loss, less than 12 months, fair value	15,433	27,511
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months, accumulated loss	(230)	(366)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, fair value	0	25,343
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	0	(1,306)
Debt securities, available-for-sale, continuous unrealized loss position, fair value	15,433	52,854
Debt securities, available-for-sale, unrealized loss position, accumulated loss	$ (230)	(1,672)
Treasury securities
Debt Securities, Available-for-sale [Abstract]
Debt securities, available-for-sale, unrealized loss, less than 12 months, fair value		0
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months, accumulated loss		0
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, fair value		7,242
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss		(143)
Debt securities, available-for-sale, continuous unrealized loss position, fair value		7,242
Debt securities, available-for-sale, unrealized loss position, accumulated loss		$ (143)

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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