Business Combinations - Acquisitions Accounted for Business Combinations (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Business Combination, Separately Recognized Transactions [Line Items]
Business Acquisitions Purchase Price Allocation Current Assets Cash And Cash Equivalents	$ 2,094
Cash Paid	42,697	$ 36,200
Business Acquisition Cost of Entity Note Payable	492
Other Payable	300
Recorded Earn-Out Payable	606
Net Assets Acquired	44,095
Maximum Potential Earn- Out Payable	5,474
SSAD [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Business Acquisitions Purchase Price Allocation Current Assets Cash And Cash Equivalents	2,094
Net Assets Acquired	$ 33,962
SSAD [Member] | Services [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Effective Date of Acquisition	Feb. 01, 2016
Cash Paid	$ 32,499
Business Acquisition Cost of Entity Note Payable	492
Other Payable	0
Recorded Earn-Out Payable	971
Net Assets Acquired	33,962
Maximum Potential Earn- Out Payable	3,000
Other Acquisitions [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Business Acquisitions Purchase Price Allocation Current Assets Cash And Cash Equivalents	0
Net Assets Acquired	10,133
Other Acquisitions [Member] | Various
Business Combination, Separately Recognized Transactions [Line Items]
Cash Paid	10,198
Business Acquisition Cost of Entity Note Payable	0
Other Payable	300
Recorded Earn-Out Payable	(365)
Net Assets Acquired	10,133
Maximum Potential Earn- Out Payable	$ 2,474