Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

Subsequent events - Narrative (Details) - Secured debt - USD ($) $ in Millions	Apr. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Senior Secured Credit Facility
Subsequent Event [Line Items]
Current borrowing capacity		$ 950.0
Senior Secured Credit Facility \| Subsequent Event
Subsequent Event [Line Items]
Current borrowing capacity	$ 725.0
Letter of Credit
Subsequent Event [Line Items]
Letters of credit outstanding		$ 14.7	$ 14.7
Letter of Credit \| Subsequent Event
Subsequent Event [Line Items]
Letters of credit outstanding	$ 44.1