401(k) Plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Employer matching contribution, percent	6.00%
Vesting period	5 years
Employer matching contribution, amount	$ 726,000	$ 683,000	$ 671,000
Discretionary contributions	$ 0	$ 0	$ 0