Components of Valuation and Qualifying Accounts (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for doubtful accounts and unbilled services
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of period	$ 178,819	$ 185,754	$ 144,825
Charged to Expense	15,386	8,912	15,564
Charged to Other Accounts	9,656	9,501	42,134
Deductions	23,174	25,348	16,769
Balance at End of Period	180,687	178,819	185,754
Valuation allowance for deferred tax asset
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of period	18,900	13,167	14,442
Charged to Expense	2,721	5,733	0
Charged to Other Accounts	0	0	0
Deductions	0	0	1,275
Balance at End of Period	$ 21,621	$ 18,900	$ 13,167