Amortizable Intangible Assets - Amortizable Intangible Assets (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	$ 1,504,378	$ 1,494,561
Accumulated Amortization	(874,095)	(853,556)
Net Carrying Value	630,283	641,005
Purchased customer accounts
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	1,474,048	1,464,274
Accumulated Amortization	(844,901)	(824,584)
Net Carrying Value	$ 629,147	639,690
Weighted Average Life (Years)	15 years
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	$ 30,330	30,287
Accumulated Amortization	(29,194)	(28,972)
Net Carrying Value	$ 1,136	$ 1,315
Weighted Average Life (Years)	6 years 9 months 18 days