Amortizable Intangible Assets - Amortizable Intangible Assets (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	$ 1,535,316	$ 1,494,561
Accumulated Amortization	(894,762)	(853,556)
Net Carrying Value	640,554	641,005
Purchased customer accounts
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	1,504,859	1,464,274
Accumulated Amortization	(865,347)	(824,584)
Net Carrying Value	$ 639,512	639,690
Weighted Average Life (Years)	15 years
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	$ 30,457	30,287
Accumulated Amortization	(29,415)	(28,972)
Net Carrying Value	$ 1,042	$ 1,315
Weighted Average Life (Years)	6 years 9 months 18 days