Supplemental Disclosures of Cash Flow Information and Non-Cash Financing and Investing Activities - Significant Non-Cash Investing and Financing Activities (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted Cash and Cash Equivalents	$ 250,705,000	$ 265,637,000	$ 229,753,000
Cash and Cash Equivalents, at Carrying Value	573,383,000	515,646,000	443,420,000
Cash paid during the period for:
Interest	36,172,000	37,652,000	37,542,000
Income taxes	152,024,000	143,111,000	132,874,000
Significant non-cash investing and financing activities
Other payables issued for purchased customer accounts	11,708,000	10,664,000	10,029,000
Estimated acquisition earn-out payables and related charges	6,921,000	4,463,000	36,899,000
Notes Assumed	0	492,000	0
Notes received on the sale of fixed assets and customer accounts	0	22,000	7,755,000
Cash and Cash Equivalents inclusive of Restricted Cash [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and Cash Equivalents, at Carrying Value	$ 824,088,000	$ 781,283,000	$ 673,173,000