Unaudited Quarterly Financial Data - Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended																12 Months Ended
		Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information
Total revenues		$ 205,204		$ 199,195		$ 192,713		$ 192,470		$ 195,169		$ 189,311		$ 190,252		$ 186,226		$ 789,582	$ 760,958	$ 752,520
Total cost of revenues (exclusive of depreciation)		99,726		99,717		97,660		97,708		99,461		93,420		92,783		89,483		394,811	375,147	379,741
Operating income		26,048	[1]	28,376	[1]	24,248	[1]	27,013	[1]	25,366	[2]	36,598	[2]	29,374	[2]	41,291	[2]	105,685	132,629	113,140
Income before income taxes		21,671	[1]	23,386	[1]	20,303	[1]	22,350	[1]	19,461	[2]	30,159	[2]	17,285	[2]	33,094	[2]	87,710	99,999	96,341
Income tax provision		(6,705)	[3]	(8,806)	[3]	(8,722)	[3]	(2,113)	[3]	(6,814)	[3]	(12,265)	[3]	(6,448)	[3]	(11,590)	[3]	$ (26,346)	$ (37,117)	$ (33,774)
Net income	[3]	$ 14,966	[1]	$ 14,580	[1]	$ 11,581	[1]	$ 20,237	[1]	$ 12,647	[2]	$ 17,894	[2]	$ 10,837	[2]	$ 21,504	[2]
Basic earnings per common share		$ 0.46	[1],[3]	$ 0.45	[1],[3]	$ 0.36	[1],[3]	$ 0.63	[1],[3]	$ 0.41	[2],[3]	$ 0.58	[2],[3]	$ 0.35	[2],[3]	$ 0.70	[2],[3]	$ 1.89	$ 2.03	$ 2.01
Diluted earnings per common share		$ 0.45	[1],[3]	$ 0.44	[1],[3]	$ 0.35	[1],[3]	$ 0.62	[1],[3]	$ 0.38	[2],[3]	$ 0.55	[2],[3]	$ 0.33	[2],[3]	$ 0.64	[2],[3]	$ 1.87	$ 1.90	$ 1.87

[1] During the first, second, third, and fourth quarters of 2017 we incurred restructuring and reorganization charges of $0.2 million, $2.7 million, $1.6 million, and $4.2 million, respectively, or $0.01, $0.05, $0.03, and $0.09 per diluted share (see Note 6).

[2] During the first, second, and fourth quarters of 2016 we incurred restructuring and reorganization charges of $(5.7) million, $5.3 million, and $1.0 million, respectively, or $(0.11), $0.10, and $0.02 per diluted share. The negative restructuring and reorganization charges in the first quarter reflect the gain on disposition of business operations (see Note 6).

[3] Fluctuations in our effective income tax rate between quarters generally relates to the accounting for discrete income tax items in any given quarter, and revisions of estimates for certain income tax components during the year. For 2017: Our effective income tax rates for the first, second, third, and fourth quarters were 9%, 43%, 38%, and 31%, respectively. The first quarter 2017 effective income tax rate reflects an approximately $5 million net benefit resulting from Comcast’s exercise of 1.4 million vested stock warrants in January 2017 (see Note 10) and the fourth quarter effective income tax rate includes a $2 million benefit from the remeasurement of U.S.-based net deferred tax liabilities as required under the U.S. Tax reform enacted in December 2017 (see Note 7). For 2016: Our effective income tax rates for the first, second, third, and fourth quarters were 35%, 37%, 41%, and 35%, respectively.