Pension and Employee Benefit Plans - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit And Contribution Plan Disclosure [Line Items]
Increase (decrease) in minimum liability after tax of defined benefit plans	$ 100,000	$ (100,000)	$ 300,000
Current Assets Mix percentage	100.00%	100.00%
Assumed average annual returns	7.25%	7.50%	7.50%
Defined benefit plan change in discount rate projected benefit obligation	$ 1,100,000
Net Periodic Pension Cost	9,000
Defined benefit plan, assumed long-term rate of return on assets	66,000
Net periodic benefit cost	$ 233,000	$ 256,000	$ (106,000)
Listing under plans Forms 5500 as providing more than 5% contribution	false
Liability has been provided in the accompanying consolidated financial statements	$ 0
Amounts charged to pension expense	2,000,000	2,100,000	1,300,000
Aggregate matching contributions and discretionary contributions Amount	$ 1,600,000	1,500,000	1,200,000
PMFG, Inc. [Member]
Defined Benefit And Contribution Plan Disclosure [Line Items]
Total cash contribution by employer			100,000
Employee Deferral Category One [Member]
Defined Benefit And Contribution Plan Disclosure [Line Items]
Profit sharing and 401(k) savings retirement plan for non-union employees Description	The plan covers substantially all employees who have 30 days of service, and who have attained 18 years of age.
Percentage of Employee salary deferral provision	100.00%
Yellow Zone
Defined Benefit And Contribution Plan Disclosure [Line Items]
Plans Funded Status Description	Between 65 and less than 80 percent
Red Zone
Defined Benefit And Contribution Plan Disclosure [Line Items]
Plans Funded Status Description	Less than 65 percent
Green Zone
Defined Benefit And Contribution Plan Disclosure [Line Items]
Plans Funded Status Description	At least 80 percent
Pension Plan [Member]
Defined Benefit And Contribution Plan Disclosure [Line Items]
Net loss for the defined benefit pension plan to be amortized in next year	$ 200,000
Prior service cost for the defined benefit pension plan to be amortized in next year	2,000
Estimated pension plan cash obligations payable in 2018	1,900,000
Estimated pension plan cash obligations payable in 2019	2,100,000
Estimated pension plan cash obligations payable in 2020	2,200,000
Estimated pension plan cash obligations payable in 2021	2,100,000
Estimated pension plan cash obligations payable in 2022	2,200,000
Estimated pension plan cash obligations payable in 2023 through 2027	10,700,000
Health Care Plan [Member]
Defined Benefit And Contribution Plan Disclosure [Line Items]
Net loss for the defined benefit pension plan to be amortized in next year	0
Prior service cost for the defined benefit pension plan to be amortized in next year	11,000
Net periodic benefit cost	$ 11,000	$ 15,000	$ 12,000
Weighted average discount rate to determine the net periodic benefit cost	2.75%	3.00%	3.75%
Estimated pension plan cash obligations payable in 2018	$ 24,000
Estimated pension plan cash obligations payable in 2019	20,000
Estimated pension plan cash obligations payable in 2020	17,000
Estimated pension plan cash obligations payable in 2021	14,000
Estimated pension plan cash obligations payable in 2022	11,000
Estimated pension plan cash obligations payable in 2023 through 2027	$ 30,000
Minimum [Member] | Debt Securities [Member]
Defined Benefit And Contribution Plan Disclosure [Line Items]
Current Assets Mix percentage	30.00%
Assumed average annual returns	4.00%
Minimum [Member] | Equity Securities [Member]
Defined Benefit And Contribution Plan Disclosure [Line Items]
Current Assets Mix percentage	60.00%
Assumed average annual returns	8.00%
Maximum [Member] | Debt Securities [Member]
Defined Benefit And Contribution Plan Disclosure [Line Items]
Current Assets Mix percentage	40.00%
Assumed average annual returns	6.00%
Maximum [Member] | Equity Securities [Member]
Defined Benefit And Contribution Plan Disclosure [Line Items]
Current Assets Mix percentage	70.00%
Assumed average annual returns	12.00%