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, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Restricted Cash and Cash Equivalents Items [Line Items]
Document Period End Date	Mar. 31, 2019
Cash and cash equivalents	$ 322,477,000	$ 558,248,000	$ 438,961,000	$ 573,383,000
Restricted Cash and Cash Equivalents	302,410,000	268,129,000	338,635,000	250,705,000
Cash paid during the period for:
Interest	20,127,000	14,472,000
Income taxes	3,120,000	3,179,000
Significant non-cash investing and financing activities
Other payable issued for purchased customer accounts	608,000	1,690,000
Estimated acquisition earn-out payables and related charges	18,155,000	4,524,000
Cash and Cash Equivalents inclusive of Restricted Cash [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and Cash Equivalents, Period Increase (Decrease)	(152,709,000)	2,289,000
Cash and cash equivalents	$ 624,887,000	$ 826,377,000	$ 777,596,000	$ 824,088,000