Unaudited Quarterly Financial Data - Quarterly Financial Information (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Information
Total revenues	$ 193,697		$ 185,003		$ 184,558		$ 188,028		$ 194,549		$ 186,180		$ 186,107		$ 180,632		$ 751,286	$ 747,468	$ 756,866
Total cost of revenues (exclusive of depreciation)	99,087		94,470		93,682		102,104		94,155		94,898		94,758		93,354		389,343	377,165	383,816
Operating income	19,125	[1]	13,831	[1]	21,820	[1]	20,914	[1]	16,435	[2]	20,553	[2]	21,681	[2]	18,035	[2]	75,690	76,704	96,574
Income before income taxes	16,715	[1]	10,064	[1]	17,741	[1]	17,002	[1]	12,482	[2]	16,631	[2]	18,862	[2]	13,544	[2]	61,522	61,519	77,224
Income tax provision	(4,083)	[3]	(4,831)	[3]	(8,338)	[3]	(7,311)	[3]	(3,401)	[3]	(1,331)	[3]	(6,790)	[3]	1,354	[3]	(24,563)	(10,168)	(28,345)
Net income	$ 12,632	[1],[3]	$ 5,233	[1],[3]	$ 9,403	[1],[3]	$ 9,691	[1],[3]	$ 9,081	[2],[3]	$ 15,300	[2],[3]	$ 12,072	[2],[3]	$ 14,898	[2],[3]
Basic earnings per common share	$ 0.39	[1],[3]	$ 0.16	[1],[3]	$ 0.29	[1],[3]	$ 0.30	[1],[3]	$ 0.28	[2],[3]	$ 0.48	[2],[3]	$ 0.38	[2],[3]	$ 0.46	[2],[3]	$ 1.14	$ 1.60	$ 1.52
Diluted earnings per common share	$ 0.38	[1],[3]	$ 0.15	[1],[3]	$ 0.28	[1],[3]	$ 0.28	[1],[3]	$ 0.27	[2],[3]	$ 0.47	[2],[3]	$ 0.37	[2],[3]	$ 0.46	[2],[3]	$ 1.10	$ 1.56	$ 1.51

[1] During the first, third, and fourth quarters of 2014 we incurred restructuring expenses of $1.2 million, $7.8 million, and $4.9 million, respectively, or $0.02, $0.12, and $0.11 per diluted share (see Note 6).

[2] During the first and fourth quarters of 2013 we incurred restructuring expenses of $0.9 and $11.5 million, respectively, or $0.03 and $0.25 per diluted share (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 2014: Our effective income tax rates for the first, second, third, and fourth quarters were 43%, 47%, 48%, and 24%, respectively. The low fourth quarter rate can be mainly attributed to full year impact of the 2014 R&D tax credits, as the legislation was not passed until December 2014.•For 2013: Our effective income tax rates for the first, second, third, and fourth quarters of 2013 were (10)%, 36%, 8%, and 27%, respectively. The negative rate in the first quarter of 2013 reflects the benefit of approximately $6 million of R&D tax credits that we generated in 2012, but were unable to include in the determination of our 2012 effective tax rate as the legislation was not signed into law until 2013. The lower income tax rates for the third and fourth quarter were mainly driven by incremental R&D income tax credits claimed for development activities from previous years and by the reduction of certain tax allowances related mainly to foreign operations, offset by increases in tax reserves for uncertainties, which provided a benefit of approximately $6 million and $2 million, respectively.