401(k) Savings Plan (Details) - Other Pension, Postretirement and Supplemental Plans [Member] - 401K Savings Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Contribution Plan Disclosure [Line Items]
Percent of employer's match of the employee's first 1% of eligible pay	100.00%
Percent of employee eligible pay (first 1%)	1.00%
Percent of employer's match of the employee's next 5% of eligible pay	50.00%
Percent of employee eligible pay (next 5%)	5.00%
Maximum employer matching, percent	3.50%
Annual vesting percentage	25.00%
Employer's match after two years (fully vested)	100.00%
Number of years until employer matches 100%	2 years
401(k) matching contributions	$ 1,105	$ 1,056	$ 1,014