Pension plan and 401(k) Program - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Expected future employer contributions, next fiscal year	$ 1,300
Employer's matching contribution, percent of match	50.00%
Employer's matching contribution, percent of employee's gross pay	6.00%
Employers matching contribution vesting percentage after two years of credited service	50.00%
Employers matching contribution vesting percentage after three years of credited service	100.00%
401k plan expense	$ 2,600	$ 2,600	$ 2,200
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 23,610	$ 24,281