Benefit Plans - Multiemployer Defined Benefit Pension Plans (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Multiemployer plans
Expenses for contributions not reimbursed by clients and related to multiemployer defined benefit and defined contribution plans	$ 2.0	$ 2.1	$ 2.0
Multiemployer defined benefit pension plans \| Teamsters Local Union 727
Multiemployer plans
Pension Protection Zone Status	Green	Green	Green
Contributions	$ 3.1	$ 3.2	$ 3.4
Multiemployer defined benefit pension plans \| Local 272 Labor Management
Multiemployer plans
Pension Protection Zone Status	Green	Green	Green
Contributions	$ 1.3	$ 1.5	$ 1.6

Indicate the multiemployer plan's certified zone status as currently required by the Pension Protection Act of 2006 or a subsequent amendment thereof. The zone status categories are red (critical status), orange (seriously endangered), yellow (endangered), and green (none of the above). The acceptable values are "red", "orange", "yellow", "green", "other", and "NA". A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 5
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450657-114947

Name:	us-gaap_MultiemployerPlansCertifiedZoneStatus
Namespace Prefix:	us-gaap_
Data Type:	us-types:zoneStatusItemType
Balance Type:	na
Period Type:	duration