Employee Benefit Plans - Projected Benefit Obligation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Change in projected benefit obligation:
Benefit obligation at beginning of period	$ 31,911	$ 28,088
Interest costs	973	1,136
Actuarial losses/(gains)	2,672	4,131
Benefits paid	(1,497)	(1,444)
Projected benefit obligation at end of period	34,059	31,911
Change in plan assets:
Plan assets at fair value at beginning of period	0	0
Company contributions	1,497	1,444
Benefits paid	(1,497)	(1,444)
Plan assets at fair value at end of period	0	0
Unfunded status of the plans	(34,059)	(31,911)
Accrued salaries and benefits	(1,727)	(1,451)
Other liabilities	(32,332)	(30,460)
Amounts recognized in the balance sheet	(34,059)	(31,911)
Amounts recognized in accumulated other comprehensive income/(loss):
Unrecognized net actuarial loss	14,792	12,617
Unrecognized prior service credit	(180)	(1,077)
Pension and other postretirement benefit plans, amount recognized in accumulated other comprehensive income	$ 14,612	$ 11,540