Changes in Carrying Amount of Goodwill (Detail) (USD $)	12 Months Ended
Changes in Carrying Amount of Goodwill (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Apr. 17, 2014
Goodwill [Line Items]
Goodwill, Beginning Balance	$ 21,498,000us-gaap_Goodwill	$ 10,166,000us-gaap_Goodwill	$ 18,600,000us-gaap_Goodwill
Business acquisition	21,493,000us-gaap_GoodwillAcquiredDuringPeriod	11,332us-gaap_GoodwillAcquiredDuringPeriod
Goodwill, Ending Balance	42,991,000us-gaap_Goodwill	21,498,000us-gaap_Goodwill	18,600,000us-gaap_Goodwill
Goodwill, Gross	45,387,000us-gaap_GoodwillGross
Accumulated impairment losses	(2,396,000)
Goodwill	42,991,000us-gaap_Goodwill	21,498,000us-gaap_Goodwill	18,600,000us-gaap_Goodwill
Lighting Fixtures and Lamps
Goodwill [Line Items]
Goodwill, Beginning Balance	21,498,000	10,166,000
Business acquisition	21,493,000	11,332,000
Transfer of Relume's Media business	(1,463,000)
Goodwill, Ending Balance	41,528,000	21,498,000
Goodwill, Gross	43,517,000
Accumulated impairment losses	(1,989,000)
Goodwill	41,528,000	21,498,000
Lighting Signage and Media
Goodwill [Line Items]
Transfer of Relume's Media business	1,463,000
Goodwill, Ending Balance	1,463,000
Goodwill, Gross	1,870,000
Accumulated impairment losses	(407,000)
Goodwill	$ 1,463,000