Commitments and Contingencies - Additional Information (Detail) $ in Millions		1 Months Ended		6 Months Ended	12 Months Ended
	May 15, 2017 USD ($)	Sep. 30, 2015 USD ($)	May 31, 2014 USD ($)	Jun. 30, 2018 USD ($) LegalMatter	Dec. 31, 2013 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2017 USD ($)
Litigation relating to occupancy tax
Commitment And Contingencies [Line Items]
Number of lawsuits filed | LegalMatter				96
Number of lawsuits currently active | LegalMatter				13
Number of lawsuits dismissed to date | LegalMatter				43
Number of dismissals based on finding that defendant was not subject to local hotel occupancy tax or the local government lacked standing to pursue claims | LegalMatter				29
Reserve for legal contingencies				$ 39.0			$ 43.0
Colorado | Litigation related to other taxes
Commitment And Contingencies [Line Items]
Possible tax assessment payments for litigation				23.0
Hawaii | Litigation related to other taxes
Commitment And Contingencies [Line Items]
Pay-to-play occupancy and other tax payments					$ 171.0
Tax refunds received		$ 132.0
Tax paid, net of refunds				44.0
Hawaii | Litigation related to other taxes | Orbitz Worldwide, Inc.
Commitment And Contingencies [Line Items]
Tax refunds received		$ 22.0
Hawaii | Hawaii Litigation Related to Other Taxes, Merchant Model Car
Commitment And Contingencies [Line Items]
Pay-to-play occupancy and other tax payments	$ 16.7
City of San Francisco
Commitment And Contingencies [Line Items]
Pay-to-play occupancy and other tax payments			$ 25.5			$ 48.0
City of San Francisco | Orbitz Worldwide, Inc.
Commitment And Contingencies [Line Items]
Pay-to-play occupancy and other tax payments, paid to date				$ 4.6