Supplemental Disclosures of Cash Flow Information and Non-Cash Financing and Investing Activities - Significant Non-Cash Investing and Financing Activities (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Restricted Cash and Cash Equivalents Items [Line Items]
Document Period End Date	Sep. 30, 2017
Cash and cash equivalents	$ 546,520,000	$ 488,683,000	$ 515,646,000	$ 443,420,000
Restricted Cash and Cash Equivalents	276,687,000	278,279,000	265,637,000	229,753,000
Cash paid during the period for:
Interest	32,504,000	33,122,000
Income taxes	110,853,000	104,739,000
Significant non-cash investing and financing activities
Other payable issued for purchased customer accounts	11,395,000	10,505,000
Estimated acquisition earn-out payables and related charges	1,332,000	3,828,000
Business Acquisition Cost of Entity Note Payable	0	492,000
Cash and Cash Equivalents inclusive of Restricted Cash [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 823,207,000	$ 766,962,000	$ 781,283,000	$ 673,173,000