Benefit Plans - 401(k) Savings Plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
401(k) Savings Plan
Maximum discretionary contribution matched by employer for each employee's contribution	$ 3,000	$ 2,500
Contribution expense	$ 934,000	$ 749,000	$ 535,000