Schedule of Total Revenue from Major Customers (Detail) (Customer Concentration Risk [Member])	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Major Customer A
Revenue, Major Customer [Line Items]
Concentration risk percentage	22.40%	13.10%	13.70%
Major Customer B
Revenue, Major Customer [Line Items]
Concentration risk percentage	29.90%	34.70%	35.20%