Business Combinations - Acquisitions Accounted for Business Combinations (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Business Combination, Separately Recognized Transactions [Line Items]
Cash Paid	$ 36,195	$ 1,000
Other Payable	5
Recorded Earn-Out Payable	5,653
Net Assets Acquired	41,853
Maximum Potential Earn- Out Payable	14,912
Liberty Insurance Brokers, Inc. and Affiliates (Liberty)
Business Combination, Separately Recognized Transactions [Line Items]
Net Assets Acquired	13,436
Liberty Insurance Brokers, Inc. and Affiliates (Liberty) | Retail
Business Combination, Separately Recognized Transactions [Line Items]
Effective Date of Acquisition	Feb. 01, 2015
Cash Paid	12,000
Other Payable	0
Recorded Earn-Out Payable	1,436
Net Assets Acquired	13,436
Maximum Potential Earn- Out Payable	3,750
Spain Agency, Inc.
Business Combination, Separately Recognized Transactions [Line Items]
Net Assets Acquired	23,431
Spain Agency, Inc. | Retail
Business Combination, Separately Recognized Transactions [Line Items]
Effective Date of Acquisition	Mar. 01, 2015
Cash Paid	20,681
Other Payable	0
Recorded Earn-Out Payable	2,750
Net Assets Acquired	23,431
Maximum Potential Earn- Out Payable	9,162
Other
Business Combination, Separately Recognized Transactions [Line Items]
Net Assets Acquired	4,986
Other | Various
Business Combination, Separately Recognized Transactions [Line Items]
Cash Paid	3,514
Other Payable	5
Recorded Earn-Out Payable	1,467
Net Assets Acquired	4,986
Maximum Potential Earn- Out Payable	$ 2,000