Debt Obligations-Other (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2016 item	Mar. 31, 2015 item	Jun. 30, 2016 USD ($) item	Feb. 22, 2016 USD ($)	Feb. 21, 2016 USD ($)	Dec. 31, 2015 USD ($)
Long-Term Debt Obligations
Line of credit borrowing capacity accordion option				$ 100,000
Principal financial covenants
Leverage ratio			3.00
Other disclosures
Current portion of capital lease obligations			$ 217			$ 251
Number of acquisitions | item	2
Shoffner
Other disclosures
Debt acquired related to coil line duct processing system			400
Outstanding balance			400
Current debt			$ 100
Other Acquisitions
Other disclosures
Number of acquisitions | item		2
London Interbank Offered Rate (LIBOR) | Shoffner
Market rates relating to interest options
Interest rate margin (as a percent)			2.25%
Additional per annum interest margin added under:
Additional per annum interest margin (as a percent)			2.25%
Revolving credit facility
Long-Term Debt Obligations
Borrowing capacity				$ 325,000	$ 250,000
Letters of credit amount outstanding			$ 41,500
Credit available			$ 247,500
Principal financial covenants
Leverage ratio			0.30
Number of quarters of capital expenditures, tax provision, dividends and stock repurchase payments used for calculation of fixed charge coverage ratio | item			4
Fixed charge coverage ratio			29.30
Number of interest rate options | item			2
Other disclosures
Weighted average interest rate (as a percent)			1.70%
Revolving credit facility | Through maturity
Principal financial covenants
Leverage ratio			2.75
Revolving credit facility | Minimum
Principal financial covenants
Fixed charge coverage ratio			2.00
Additional per annum interest margin added under:
Letter of credit fees (as a percent)			1.25%
Commitment fees payable on unused portion of the facility (as a percent)			0.20%
Revolving credit facility | Minimum | Covenant Requirement
Principal financial covenants
Net leverage ratio used as basis for other restrictions			2.00
Revolving credit facility | Maximum
Principal financial covenants
Amount of stock repurchases to maintain maximum net leverage ratio			$ 25,000
Net leverage ratio after giving effect to stock repurchases for calculation of the fixed charge coverage ratio			1.50
Permitted amount of acquisitions per transaction			$ 30,000
Aggregate purchase price of current acquisition and acquisitions in the preceding 12 month period for determining permitted amount of acquisition per transaction			$ 65,000
Additional per annum interest margin added under:
Letter of credit fees (as a percent)			2.00%
Commitment fees payable on unused portion of the facility (as a percent)			0.35%
Revolving credit facility | Maximum | Covenant Requirement
Principal financial covenants
Net leverage ratio used to determine exclusion of stock repurchases and the payment of dividends for calculation of the fixed charge coverage ratio			1.50
Revolving credit facility | Base rate | Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: Less than 0.75
Market rates relating to interest options
Interest rate margin (as a percent)			0.25%
Additional per annum interest margin added under:
Additional per annum interest margin (as a percent)			0.25%
Revolving credit facility | Base rate | Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 0.75 to 1.50
Market rates relating to interest options
Interest rate margin (as a percent)			0.50%
Additional per annum interest margin added under:
Additional per annum interest margin (as a percent)			0.50%
Revolving credit facility | Base rate | Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 1.50 to 2.25
Market rates relating to interest options
Interest rate margin (as a percent)			0.75%
Additional per annum interest margin added under:
Additional per annum interest margin (as a percent)			0.75%
Revolving credit facility | Base rate | Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 2.25 or greater
Market rates relating to interest options
Interest rate margin (as a percent)			0.75%
Additional per annum interest margin added under:
Additional per annum interest margin (as a percent)			0.75%
Revolving credit facility | Eurodollar rate | Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: Less than 0.75
Market rates relating to interest options
Interest rate margin (as a percent)			1.25%
Additional per annum interest margin added under:
Additional per annum interest margin (as a percent)			1.25%
Revolving credit facility | Eurodollar rate | Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 0.75 to 1.50
Market rates relating to interest options
Interest rate margin (as a percent)			1.50%
Additional per annum interest margin added under:
Additional per annum interest margin (as a percent)			1.50%
Revolving credit facility | Eurodollar rate | Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 1.50 to 2.25
Market rates relating to interest options
Interest rate margin (as a percent)			1.75%
Additional per annum interest margin added under:
Additional per annum interest margin (as a percent)			1.75%
Revolving credit facility | Eurodollar rate | Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 2.25 or greater
Market rates relating to interest options
Interest rate margin (as a percent)			2.00%
Additional per annum interest margin added under:
Additional per annum interest margin (as a percent)			2.00%
Notes to former owners
Other disclosures
Outstanding balance			$ 2,800
Notes to former owners | Shoffner
Other disclosures
Weighted average interest rate (as a percent)			3.00%
Outstanding balance			$ 1,800
Notes to former owners | Other Acquisitions
Other disclosures
Weighted average interest rate (as a percent)			2.50%
Outstanding balance			$ 1,000
Other debt | Dyna Ten
Other disclosures
Capital lease obligation pertaining to acquisition			400
Current portion of capital lease obligations			$ 200