Supplemental Disclosures of Cash Flow Information and Non-Cash Financing and Investing Activities - Significant Non-Cash Investing and Financing Activities (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Restricted Cash and Cash Equivalents Items [Line Items]
Document Period End Date	Mar. 31, 2018
Cash and cash equivalents	$ 558,248,000	$ 546,721,000	$ 573,383,000	$ 515,646,000
Restricted Cash and Cash Equivalents	268,129,000	279,368,000	250,705,000	265,637,000
Cash paid during the period for:
Interest	14,472,000	14,531,000
Income taxes	3,179,000	2,704,000
Significant non-cash investing and financing activities
Other payable issued for purchased customer accounts	1,690,000	0
Estimated acquisition earn-out payables and related charges	4,524,000	(211,000)
Cash and Cash Equivalents inclusive of Restricted Cash [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 826,377,000	$ 826,089,000	$ 824,088,000	$ 781,283,000