Consolidated Statements of Comprehensive Income (Loss) - USD ($)	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
Income Statement [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
Operating expenses
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
Goodwill impairment charge											83,752,000
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
Other income (expense)
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)
Other (expense) income									(59,125,000)	(46,015,000)	(49,628,000)
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 (loss) 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 (loss) 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)
Other comprehensive loss, net of tax
Foreign currency translation adjustments, net of tax expense of $0									$ (28,727,000)	$ (29,179,000)	$ (9,720,000)
Other comprehensive loss, net of tax									(28,727,000)	(29,179,000)	(9,720,000)
Comprehensive income (loss)									$ 37,326,000	$ 29,628,000	$ (20,314,000)