Borrowing Arrangements (Details) - USD ($) $ in Thousands		9 Months Ended	12 Months Ended
		Sep. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Other borrowings		$ 20,724	$ 23,172
FHLB borrowings		659,204	832,527
Other borrowings:
Debt Instrument [Line Items]
Other borrowings		20,724	23,172
Average amount outstanding during the period	[1]	22,387	91,940
Maximum amount outstanding during the period	[2]	$ 24,549	$ 219,259
Weighted average interest rate during the period	[3]	0.20%	0.40%
Interest rate at end of the period	[4]	0.20%	0.10%
FHLB borrowings:
Debt Instrument [Line Items]
FHLB borrowings		$ 659,204	$ 832,527
Average amount outstanding during the period	[1]	684,280	1,032,269
Maximum amount outstanding during the period	[2]	$ 723,584	$ 1,274,370
Weighted average interest rate during the period	[3]	1.10%	1.10%
Interest rate at end of the period	[5]	1.10%	1.00%

[1] The average amount outstanding during the period was computed by dividing the total daily outstanding principal balances by the number of days in the period.

[2] The maximum amount outstanding at any month-end during the period.

[3] The weighted average interest rate during the period was computed by dividing the actual interest expense (annualized for interim periods) by the average amount outstanding during the period. The weighted average interest rate on the FHLB borrowings includes the effect of interest rate swaps.

[4] Stated rate.

[5] The interest rate on the FHLB borrowings includes the effect of interest rate swaps.