Pension plan and 401(k) Program - Aggregate Information of Projected Benefit in Excess of Benefit Obligation (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Retirement Benefits [Abstract]
Projected benefit obligation	$ 30,772	$ 30,185
Accumulated benefit obligation	$ 30,583	$ 29,985

Amount of accumulated benefit obligation for defined benefit pension plan with projected benefit obligation in excess of plan assets.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e2417-114920

Name:	us-gaap_DefinedBenefitPlanPensionPlanWithProjectedBenefitObligationInExcessOfPlanAssetsAccumulatedBenefitObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant