Disposition of Business - Additional Information (Detail) - USD ($) $ in Thousands		12 Months Ended
	May 22, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Pre-tax gain on disposal of business		$ 0	$ 0	$ 508,810
Disposal Group, Not Discontinued Operations | eLong, Inc
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Percentage of ownership sold	62.40%
Consideration of business sold	$ 671,000
Consideration of business sold, net of costs to sell	$ 666,000
Pre-tax gain on disposal of business				508,810
Gain on disposal of business, after-tax				395,000
Disposal Group, Not Discontinued Operations | eLong, Inc | Long-term investments and other assets
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Held in escrow				$ 67,000