Acquisitions - Fair Values of Assets Acquired and Liabilities Assumed at Date of Closing of Acquisition (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Dec. 31, 2012
Business Acquisition [Line Items]
Goodwill	$ 144,267	$ 132,220	$ 19,548
Aarding Thermal Acoustics B.V. ("Aarding") [Member]
Business Acquisition [Line Items]
Current assets	15,062
Property and equipment	959
Goodwill	7,595
Intangible assets - finite life	13,477
Intangible assets - indefinite life	2,865
Total assets acquired	39,958
Current liabilities assumed	(8,277)
Deferred income tax liability	(4,086)
Net assets acquired	$ 27,595