Schedule of Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, shares in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 442,204,000	$ 455,470,000	$ 449,137,000	$ 432,338,000	$ 425,158,000	$ 451,178,000	$ 454,324,000	$ 425,552,000	$ 1,779,149,000	$ 1,756,212,000	$ 1,652,432,000
Direct cost of revenues	299,336,000	301,609,000	291,469,000	279,030,000	281,689,000	293,244,000	295,549,000	274,275,000	1,171,444,000	1,144,757,000	1,042,061,000
Selling, general and administrative expenses	116,351,000	105,058,000	109,045,000	102,214,000	115,965,000	102,461,000	107,032,000	108,387,000	432,668,000	433,845,000	394,681,000
Special charges					1,628,000	5,347,000	9,364,000		0	16,339,000	38,414,000
Acquisition-related contingent consideration	(55,000)	159,000	(1,538,000)	234,000	(85,000)	257,000	(5,000)	(1,843,000)	(1,200,000)	(1,676,000)	(10,869,000)
Amortization of other intangible assets	2,807,000	2,900,000	3,007,000	3,012,000	4,055,000	3,398,000	3,452,000	4,616,000	11,726,000	15,521,000	22,954,000
Costs and Expenses, Total	418,439,000	409,726,000	401,983,000	384,490,000	403,252,000	404,707,000	415,392,000	385,435,000	1,614,638,000	1,608,786,000	1,570,993,000
Operating income	23,765,000	45,744,000	47,154,000	47,848,000	21,906,000	46,471,000	38,932,000	40,117,000	164,511,000	147,426,000	81,439,000
Interest income and other	392,000	2,027,000	950,000	(137,000)	1,205,000	1,014,000	1,448,000	1,003,000	3,232,000	4,670,000	1,748,000
Interest expense	(6,231,000)	(11,696,000)	(12,473,000)	(12,368,000)	(12,488,000)	(12,634,000)	(12,908,000)	(12,655,000)	(42,768,000)	(50,685,000)	(51,376,000)
Loss on early extinguishment of debt		(19,589,000)							(19,589,000)
Income before income tax provision	17,926,000	16,486,000	35,631,000	35,343,000	10,623,000	34,851,000	27,472,000	28,465,000	105,386,000	101,411,000	31,811,000
Income tax provision	7,577,000	6,177,000	13,922,000	11,657,000	9,702,000	12,329,000	10,225,000	10,348,000	39,333,000	42,604,000	42,405,000
Net income (loss)	$ 10,349,000	$ 10,309,000	$ 21,709,000	$ 23,686,000	$ 921,000	$ 22,522,000	$ 17,247,000	$ 18,117,000	$ 66,053,000	$ 58,807,000	$ (10,594,000)
Earnings per common share — basic	$ 0.25	$ 0.25	$ 0.53	$ 0.59	$ 0.02	$ 0.57	$ 0.43	$ 0.46	$ 1.62	$ 1.48	$ (0.27)
Earnings per common share — diluted	$ 0.25	$ 0.25	$ 0.52	$ 0.57	$ 0.02	$ 0.55	$ 0.42	$ 0.45	$ 1.58	$ 1.44	$ (0.27)
Weighted average number of common shares outstanding — basic	41,078	41,094	40,792	40,384	39,991	39,789	39,681	39,438	40,846	39,726	39,188
Diluted	41,879	41,982	41,696	41,324	41,090	40,819	40,750	40,457	41,729	40,729	39,188