Amortizable Intangible Assets - Amortizable Intangible Assets (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	$ 1,890,206	$ 1,837,873
Accumulated Amortization	(990,623)	(939,066)
Net Carrying Value	899,583	898,807
Purchased customer accounts
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	1,856,534	1,804,404
Accumulated Amortization	(960,399)	(909,415)
Net Carrying Value	$ 896,135	$ 894,989
Weighted Average Life (Years)	15 years	14 years 10 months 24 days
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	$ 33,672	$ 33,469
Accumulated Amortization	(30,224)	(29,651)
Net Carrying Value	$ 3,448	$ 3,818
Weighted Average Life (Years)	4 years 6 months	4 years 6 months