Selected Quarterly Financial Information (Unaudited) (Details) (USD $)	3 Months Ended									12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011		Mar. 31, 2011	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Selected Quarterly Financial Information [Abstract]
Revenue	$ 270,543,000	$ 279,390,000	$ 274,398,000	$ 280,627,000	$ 267,954,000	$ 272,474,000	$ 262,739,000		$ 256,636,000	$ 1,104,958,000		$ 1,059,803,000		$ 926,289,000
Gross profit	53,476,000	54,720,000	55,528,000	55,685,000	56,269,000	57,742,000	56,960,000		54,330,000	219,409,000		225,301,000		193,963,000
Operating and administrative expenses	45,472,000	45,711,000	47,664,000	48,296,000	48,672,000	53,321,000	43,256,000	[1]	51,577,000	187,143,000		196,826,000		185,958,000
Restructuring and other related costs					8,100,000	0	0		0	0		8,100,000		0
Operating profit	8,004,000	9,009,000	7,864,000	7,389,000	(503,000)	4,421,000	13,704,000		2,753,000	32,266,000	[2],[3],[4]	20,375,000	[2],[3],[4]	(307,000)	[2],[3],[4]
Income before income taxes	7,918,000	8,962,000	7,784,000	7,351,000	(526,000)	4,358,000	13,588,000		2,710,000	32,015,000		20,130,000		(3,146,000)
Net income (loss)	5,042,000	5,406,000	5,071,000	3,914,000	(618,000)	2,862,000	12,016,000		740,000	19,433,000		15,000,000		(10,814,000)
Net income (loss) attributable to CDI	4,992,000	5,349,000	4,952,000	3,823,000	(657,000)	2,814,000	11,982,000		694,000	19,116,000		14,833,000		(10,858,000)
Earnings (loss) per common share:
Basic (in dollars per share)	$ 0.26	$ 0.27	$ 0.26	$ 0.20	$ (0.03)	$ 0.15	$ 0.62		$ 0.04	$ 0.99		$ 0.77		$ (0.57)
Diluted (in dollars per share)	$ 0.25	$ 0.27	$ 0.25	$ 0.20	$ (0.03)	$ 0.15	$ 0.62		$ 0.04	$ 0.97		$ 0.77		$ (0.57)
Operating and Administrative Expenses [Member]
Earnings (loss) per common share:
Benefit related to settlement							9,700,000
Unfavorable Regulatory Action [Member] | Operating and Administrative Expenses [Member]
Earnings (loss) per common share:
Benefit related to settlement							$ 9,700,000

[1] The second quarter Operating and administrative expenses included a $9.7 million benefit related to the successful legal appeal of the UK Office of Fair Trading matter.

[2] In 2011, the Company recorded an aggregate pre-tax charge of $8.1 million to "Restructuring and other related costs" in the consolidated statement of operations. The following table summarizes the amount of restructuring and other related costs recognized during the year ended December 31, 2011, by reporting segment: 2011 GETS $4,467PSS 2,622MRI 372Corporate 639Restructuring and other related costs $8,100

[3] In 2011, the Company's PSS segment recorded a $9.7 million benefit related to the successful legal appeal of the UK OFT matter.

[4] In 2010, the Company's PSS segment recorded an $8.3 million goodwill impairment charge.