Business Combinations - Estimated Fair Values of Aggregate Assets and Liabilities Acquired (Details) $ in Thousands	Sep. 30, 2019 USD ($)
Fair Value Of Assets And Liabilities Statement [Line Items]
Cash	$ 3,217
Other current assets	9,063
Fixed assets	395
Goodwill	275,307
Other assets	55
Total assets acquired	393,279
Other current liabilities	(336)
Other liabilities	(407)
Total liabilities assumed	(743)
Net assets acquired	392,536
Purchased Customer Accounts
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	104,930
Non-compete Agreements
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	312
Smith
Fair Value Of Assets And Liabilities Statement [Line Items]
Other current assets	473
Fixed assets	39
Goodwill	16,249
Total assets acquired	23,302
Other current liabilities	(469)
Total liabilities assumed	(469)
Net assets acquired	22,833
Smith | Purchased Customer Accounts
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	6,500
Smith | Non-compete Agreements
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	41
Pipino
Fair Value Of Assets And Liabilities Statement [Line Items]
Other current assets	819
Fixed assets	112
Goodwill	16,765
Other assets	772
Total assets acquired	29,839
Other current liabilities	(3,463)
Total liabilities assumed	(3,463)
Net assets acquired	26,376
Pipino | Purchased Customer Accounts
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	11,360
Pipino | Non-compete Agreements
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	11
Cossio
Fair Value Of Assets And Liabilities Statement [Line Items]
Other current assets	17
Fixed assets	29
Goodwill	11,319
Total assets acquired	15,710
Net assets acquired	15,710
Cossio | Purchased Customer Accounts
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	4,324
Cossio | Non-compete Agreements
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	21
Medval
Fair Value Of Assets And Liabilities Statement [Line Items]
Cash	3,217
Other current assets	1,708
Fixed assets	50
Goodwill	19,108
Other assets	15
Total assets acquired	31,399
Other current liabilities	(480)
Other liabilities	(29)
Total liabilities assumed	(509)
Net assets acquired	30,890
Medval | Purchased Customer Accounts
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	7,300
Medval | Non-compete Agreements
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	1
United
Fair Value Of Assets And Liabilities Statement [Line Items]
Other current assets	477
Fixed assets	20
Goodwill	15,111
Total assets acquired	22,684
Other current liabilities	(41)
Total liabilities assumed	(41)
Net assets acquired	22,643
United | Purchased Customer Accounts
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	7,065
United | Non-compete Agreements
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	11
Twinbrook
Fair Value Of Assets And Liabilities Statement [Line Items]
Fixed assets	85
Goodwill	19,839
Total assets acquired	28,493
Other current liabilities	(277)
Total liabilities assumed	(277)
Net assets acquired	28,216
Twinbrook | Purchased Customer Accounts
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	8,557
Twinbrook | Non-compete Agreements
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	12
IRS
Fair Value Of Assets And Liabilities Statement [Line Items]
Other current assets	1,200
Fixed assets	11
Goodwill	24,040
Total assets acquired	34,508
Other current liabilities	(126)
Total liabilities assumed	(126)
Net assets acquired	34,382
IRS | Purchased Customer Accounts
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	9,246
IRS | Non-compete Agreements
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	11
Other
Fair Value Of Assets And Liabilities Statement [Line Items]
Other current assets	(6,173)
Fixed assets	(166)
Goodwill	23,523
Other assets	(732)
Total assets acquired	27,312
Other current liabilities	5,556
Total liabilities assumed	5,556
Net assets acquired	32,868
Other | Purchased Customer Accounts
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	10,732
Other | Non-compete Agreements
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	128
WBR
Fair Value Of Assets And Liabilities Statement [Line Items]
Other current assets	169
Fixed assets	10
Goodwill	9,376
Total assets acquired	13,611
Other current liabilities	(166)
Other liabilities	(378)
Total liabilities assumed	(544)
Net assets acquired	13,067
WBR | Purchased Customer Accounts
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	4,022
WBR | Non-compete Agreements
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	34
Yozell
Fair Value Of Assets And Liabilities Statement [Line Items]
Other current assets	1,473
Fixed assets	12
Goodwill	9,212
Total assets acquired	14,268
Net assets acquired	14,268
Yozell | Purchased Customer Accounts
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	3,550
Yozell | Non-compete Agreements
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	21
CKP
Fair Value Of Assets And Liabilities Statement [Line Items]
Other current assets	8,900
Fixed assets	193
Goodwill	110,765
Total assets acquired	152,153
Other current liabilities	(870)
Total liabilities assumed	(870)
Net assets acquired	151,283
CKP | Purchased Customer Accounts
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	32,274
CKP | Non-compete Agreements
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	$ 21