Business Combinations - Acquisitions Accounted for Business Combinations (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Business Combination, Separately Recognized Transactions [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	$ 1,414
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	41,204
Cash Paid	33,576
Other Payable	1,690
Recorded Earn-Out Payable	4,524
Net Assets Acquired	39,790
Maximum Potential Earn- Out Payable	6,520
Fixed assets	21
Goodwill	31,367
Purchased customer accounts	9,774
Non-compete agreements	42
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other	1,414
Services
Business Combination, Separately Recognized Transactions [Line Items]
Goodwill	31,356
Other Acquisitions [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	1,414
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	41,204
Net Assets Acquired	39,790
Fixed assets	21
Goodwill	31,367
Purchased customer accounts	9,774
Non-compete agreements	42
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other	1,414
Other Acquisitions [Member] | Various
Business Combination, Separately Recognized Transactions [Line Items]
Cash Paid	33,576
Other Payable	1,690
Recorded Earn-Out Payable	4,524
Net Assets Acquired	39,790
Maximum Potential Earn- Out Payable	$ 6,520