Segment Information - Summarized Financial Information Reportable Segments (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Total revenues	$ 424,173	$ 404,298
Investment income	418	220
Amortization	21,610	21,625
Depreciation	5,318	5,183
Interest expense	9,897	9,851
Income before income taxes	102,549	93,778
Total assets	4,992,960	4,838,942	$ 5,004,479
Capital expenditures	4,252	3,727
Operating Segments | Services
Segment Reporting Information [Line Items]
Total revenues	232,188	218,344
Investment income	21	22
Amortization	10,989	10,934
Depreciation	1,637	1,642
Interest expense	10,403	10,158
Income before income taxes	50,452	47,009
Total assets	3,531,100	3,305,917
Capital expenditures	1,049	1,424
Operating Segments | National Programs
Segment Reporting Information [Line Items]
Total revenues	101,070	99,555
Investment income	248	45
Amortization	7,108	7,235
Depreciation	1,929	1,766
Interest expense	12,590	14,955
Income before income taxes	13,803	9,476
Total assets	2,499,870	2,407,695
Capital expenditures	1,932	1,489
Operating Segments | Wholesale Brokerage
Segment Reporting Information [Line Items]
Total revenues	53,414	51,828
Investment income	3	72
Amortization	2,442	2,423
Depreciation	496	563
Interest expense	247	229
Income before income taxes	14,562	14,484
Total assets	888,745	858,149
Capital expenditures	592	451
Operating Segments | Services
Segment Reporting Information [Line Items]
Total revenues	36,568	34,788
Investment income	64	0
Amortization	1,065	1,023
Depreciation	487	530
Interest expense	1,236	1,599
Income before income taxes	5,052	4,502
Total assets	324,269	300,155
Capital expenditures	205	240
Other
Segment Reporting Information [Line Items]
Total revenues	933	(217)
Investment income	82	81
Amortization	6	10
Depreciation	769	682
Interest expense	(14,579)	(17,090)
Income before income taxes	18,680	18,307
Total assets	(2,251,024)	(2,032,974)
Capital expenditures	$ 474	$ 123