Quarterly Financial Data (Unaudited) (Details) (USD $)	3 Months Ended																12 Months Ended
	Jan. 31, 2013		Oct. 31, 2012		Jul. 31, 2012		Apr. 30, 2012		Jan. 31, 2012		Oct. 31, 2011		Jul. 31, 2011		Apr. 30, 2011		Jan. 31, 2013		Jan. 31, 2012
Quarterly Financial Data (Unaudited) [Abstract]
Net revenues	$ 43,844,000		$ 49,921,000		$ 47,329,000		$ 43,453,000		$ 40,315,000		$ 40,498,000		$ 37,516,000		$ 37,078,000		$ 184,547,000		$ 155,407,000
Gross profit	10,600,000		13,977,000		12,810,000		11,321,000		9,788,000		9,468,000		9,068,000		9,261,000		48,708,000		37,585,000
Net income (loss) from continuing operations attributable to NTS	(298,000)	[1]	2,185,000	[1]	1,614,000	[1]	946,000	[1]	(559,000)		100,000		763,000		568,000		(4,447,000)		(872,000)
Net loss from discontinued operations attributable to NTS	$ 0		$ 1,000		$ (12,000)		$ 8,000		$ (59,000)		$ (287,000)		$ (26,000)		$ (9,000)		$ (3,000)		$ (381,000)
Basic earnings (loss) per common share [Abstract]
Net income (loss) from continuing operations attributable to NTS (in dollars per share)	$ (0.03)	[1]	$ 0.19	[1]	$ 0.14	[1]	$ 0.08	[1]	$ (0.05)		$ 0.01		$ 0.07		$ 0.06		$ 0.39		$ 0.08
Net income (loss) from discontinued operations (in dollars per share)	$ 0		$ 0		$ 0		$ 0		$ (0.01)		$ (0.03)		$ 0		$ 0		$ 0		$ (0.04)
Net income attributable to NTS * (in dollars per share)	$ (0.03)	[1]	$ 0.19	[1]	$ 0.14	[1]	$ 0.08	[1]	$ (0.05)		$ (0.02)		$ 0.07		$ 0.05		$ 0.39	[1]	$ 0.05	[1]
Diluted earnings per common share [Abstract]
Net income from continuing operations attributable to NTS (in dollars per share)	$ (0.03)	[1]	$ 0.18	[1]	$ 0.14	[1]	$ 0.08	[1]	$ (0.05)		$ 0.01		$ 0.07		$ 0.05		$ 0.37		$ 0.08
Net income (loss) from discontinued operations attributable to NTS (in dollars per share)	$ 0		$ 0		$ 0		$ 0		$ 0	[1]	$ (0.02)	[1]	$ 0	[1]	$ 0	[1]	$ 0		$ (0.03)
Net income attributable to NTS * (in dollars per share)	$ (0.03)	[1]	$ 0.18	[1]	$ 0.13	[1]	$ 0.08	[1]	$ (0.05)		$ (0.02)		$ 0.07		$ 0.05		$ 0.37	[1]	$ 0.04	[1]
Weighted average common shares outstanding (in shares)	11,459,000		11,384,000		11,340,000		11,320,000		11,300,000		11,299,000		10,616,000		10,243,000		11,376,000		10,865,000
Dilutive effect of stock options (in shares)	596,000		610,000		552,000		506,000		501,000		467,000		395,000		407,000		576,000		374,000
Weighted average common shares outstanding, assuming dilution (in shares)	12,055,000		11,994,000		11,892,000		11,826,000		11,801,000		11,766,000		11,011,000		10,650,000		11,952,000		11,239,000

[1] Per share data may not always add to the total for the year because each figure is independently calculated.