Acquisitions - Fair Values of Assets and Liabilities Assumed at Date of Closing after Company Finalized Purchase Accounting - PMFG (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Goodwill	$ 166,951	$ 170,153	$ 220,163
PMFG, Inc. [Member]
Business Acquisition [Line Items]
Current assets (including cash of $27,100)		92,293
Property and equipment		24,787
Other assets		953
Assets held for sale		950
Goodwill		59,860
Intangible – finite life		29,940
Intangible – indefinite life		10,280
Total assets acquired		219,063
Current liabilities assumed		(73,364)
Deferred income tax liability		(800)
Long term liabilities assumed		(3,961)
Noncontrolling interest		(4,212)
Net assets acquired		$ 136,726