Amortizable Intangible Assets - Amortizable Intangible Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	$ 1,837,873	$ 1,494,561
Accumulated Amortization	(939,066)	(853,556)
Net Carrying Value	898,807	641,005
Purchased customer accounts
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	1,804,404	1,464,274
Accumulated Amortization	(909,415)	(824,584)
Net Carrying Value	$ 894,989	$ 639,690
Weighted Average Life (Years)	14 years 10 months 24 days	15 years
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	$ 33,469	$ 30,287
Accumulated Amortization	(29,651)	(28,972)
Net Carrying Value	$ 3,818	$ 1,315
Weighted Average Life (Years)	4 years 6 months	4 years 7 months 6 days