Commitments And Contingencies (Ground Lease Agreements) (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Commitments And Contingencies [Abstract]
Ground lease expense incurred	$ 2.3	$ 2.6	$ 1.5

Operating Lease, Expense, Including Sublease Rentals

No definition available.

Name:	cli_OperatingLeaseExpenseIncludingSubleaseRentals
Namespace Prefix:	cli_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration