Summary of Significant Accounting Policies - Customers with Revenues Greater than 10% (Detail)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Caterpillar Inc. [Member]
Revenue, Major Customer [Line Items]
Customers with revenues greater than 10%	17.30%	17.70%	21.70%
Komatsu Ltd. [Member]
Revenue, Major Customer [Line Items]
Customers with revenues greater than 10%	12.10%	12.00%	14.70%
Hitachi Construction Machinery Co., Ltd. [Member]
Revenue, Major Customer [Line Items]
Customers with revenues greater than 10%			10.20%