Employee Benefit Plans (Details) - Employee Stock Ownership and Profit Sharing Plan $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) h shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($)
Employee benefit plans
Minimum service period required to participate in Plan	90 days
Percentage of employee's deferred compensation up to which the employer matches (as a percent)	4.00%
Employer's matching contribution on the next 2% of employee contribution (as a percent)	50.00%
Employee contribution after matching contribution of employer (as a percent)	2.00%
Employee's eligible compensation on which employer pays fixed contribution (as a percent)	2.00%
Common stock held in relation to employee benefit plans (in shares) | shares	824,466	852,128
Minimum service period required to be eligible to get employer's contribution	5 years
Minimum working hours required per year to be eligible to get employer's contribution | h	1,000
Employee deferral that is always vested (as a percent)	100.00%
Contribution expense | $	$ 5,700	$ 5,480	$ 4,870