Selected Quarterly Financial Data (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Nov. 30, 2012	Aug. 31, 2012	May 31, 2012	Feb. 29, 2012	Nov. 30, 2011	Aug. 31, 2011	May 31, 2011	Feb. 28, 2011	Nov. 30, 2012	Nov. 30, 2011	Nov. 30, 2010
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 91,271	$ 78,317	$ 78,404	$ 87,213	$ 93,544	$ 88,681	$ 90,955	$ 87,524	$ 335,205	$ 360,704	$ 351,610
Gross profit	80,184	67,092	67,804	76,562	82,536	77,037	79,207	76,656	291,642	315,436	310,457
Income from operations	15,692	8,405	6,122	19,221	28,422	21,430	27,566	23,823	49,440	101,241	91,476
Income from continuing operations	10,775	5,353	4,527	11,949	17,221	14,426	18,432	16,263	32,604	66,342	62,568
Net income (loss)	$ 36,025	$ 5,838	$ (1,908)	$ 7,489	$ 12,175	$ 9,059	$ 17,919	$ 20,476	$ 47,444	$ 59,629	$ 48,098
Continuing operations per share, basic (in dollars per share)	$ 0.17	$ 0.08	$ 0.07	$ 0.19	$ 0.27	$ 0.22	$ 0.28	$ 0.24	$ 0.52	$ 1.01	$ 0.98
Continuing operations per share, diluted (in dollars per share)	$ 0.17	$ 0.08	$ 0.07	$ 0.19	$ 0.27	$ 0.21	$ 0.27	$ 0.23	$ 0.51	$ 0.98	$ 0.94