Business Combinations - Estimated Fair Values of Aggregate Assets and Liabilities Acquired (Details) $ in Thousands	Mar. 31, 2020 USD ($)
Fair Value Of Assets And Liabilities Statement [Line Items]
Other current assets	$ 4,160
Fixed assets	486
Goodwill	135,482
Total assets acquired	182,626
Other current liabilities	(13,810)
Total liabilities assumed	(13,810)
Net assets acquired	168,816
Special Risk
Fair Value Of Assets And Liabilities Statement [Line Items]
Other current assets	2,159
Fixed assets	346
Goodwill	55,607
Total assets acquired	73,145
Other current liabilities	551
Total liabilities assumed	551
Net assets acquired	73,696
Texas Risk
Fair Value Of Assets And Liabilities Statement [Line Items]
Other current assets	446
Fixed assets	27
Goodwill	8,488
Total assets acquired	12,660
Other current liabilities	(1,680)
Total liabilities assumed	(1,680)
Net assets acquired	10,980
Colonial
Fair Value Of Assets And Liabilities Statement [Line Items]
Other current assets	808
Fixed assets	59
Goodwill	26,030
Total assets acquired	36,333
Other current liabilities	(1,130)
Total liabilities assumed	(1,130)
Net assets acquired	35,203
RLA
Fair Value Of Assets And Liabilities Statement [Line Items]
Fixed assets	54
Goodwill	44,592
Total assets acquired	57,676
Other current liabilities	(11,443)
Total liabilities assumed	(11,443)
Net assets acquired	46,233
Other
Fair Value Of Assets And Liabilities Statement [Line Items]
Other current assets	747
Goodwill	765
Total assets acquired	2,812
Other current liabilities	(108)
Total liabilities assumed	(108)
Net assets acquired	2,704
Purchased Customer Accounts
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	41,792
Purchased Customer Accounts | Special Risk
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	14,897
Purchased Customer Accounts | Texas Risk
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	3,674
Purchased Customer Accounts | Colonial
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	9,393
Purchased Customer Accounts | RLA
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	12,549
Purchased Customer Accounts | Other
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	1,279
Non-compete Agreements
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	706
Non-compete Agreements | Special Risk
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	136
Non-compete Agreements | Texas Risk
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	25
Non-compete Agreements | Colonial
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	43
Non-compete Agreements | RLA
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	481
Non-compete Agreements | Other
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	$ 21