Amortizable Intangible Assets - Amortizable Intangible Assets (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	$ 1,488,566		$ 1,477,348
Accumulated Amortization	(832,512)		(769,894)
Net Carrying Value	656,054		707,454
Purchased customer accounts
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	1,458,405		1,447,680
Accumulated Amortization	(803,764)		(741,770)
Net Carrying Value	$ 654,641		705,910
Weighted Average Life (Years)	15 years	15 years
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	$ 30,161		29,668
Accumulated Amortization	(28,748)		(28,124)
Net Carrying Value	$ 1,413		$ 1,544
Weighted Average Life (Years)	6 years 9 months 18 days	6 years 9 months 18 days