Debt Obligations - Other (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021 USD ($) item	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)
Debt Obligations
Payments on term loan	$ 7,500	$ 9,375
Outstanding balance	172,000		$ 236,000
Reconciliation of Credit Facility Adjusted EBITDA to net income
Net income	26,491	17,716
Provision for income taxes	8,737	6,751
Stock-based compensation	$ 4,711	$ 3,631
Principal financial covenants
Fixed charge coverage ratio	2.00
Revolving credit facility
Debt Obligations
Borrowing capacity	$ 450,000
Outstanding borrowings	10,000
Outstanding balance	10,000		70,000
Letters of credit amount outstanding	49,500
Credit available	$ 390,500
Principal financial covenants
Number of interest rate options | item	2
Leverage ratio	0.6
Fixed charge coverage ratio	28.5
Number of quarters of capital expenditures, tax provision, dividends and stock repurchase payments used for calculation of fixed charge coverage ratio | item	4
Other disclosures
Weighted average interest rate (as a percent)	1.40%
Revolving credit facility | Through maturity
Principal financial covenants
Leverage ratio	3.00
Revolving credit facility | Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: Less than 1.00
Debt Instrument, Interest Rate, Effective Percentage [Abstract]
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 | Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 2.50 or greater
Debt Instrument, Interest Rate, Effective Percentage [Abstract]
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 | Minimum
Principal financial covenants
Fixed charge coverage ratio	1.50
Revolving credit facility | Minimum | Covenant Requirement
Principal financial covenants
Net leverage ratio used as basis for other restrictions	2.50
Revolving credit facility | Maximum
Principal financial covenants
Permitted amount of acquisitions per transaction	$ 5,000
Aggregate purchase price of current acquisition and acquisitions in the preceding 12 month period for determining permitted amount of acquisition per transaction	$ 10,000
Revolving credit facility | Base Rate | Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: Less than 1.00
Debt Instrument, Interest Rate, Effective Percentage [Abstract]
Additional per annum interest margin (as a percent)	0.25%
Revolving credit facility | Base Rate | Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 1.00 to 1.75
Debt Instrument, Interest Rate, Effective Percentage [Abstract]
Additional per annum interest margin (as a percent)	0.50%
Revolving credit facility | Base Rate | Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 1.75 to 2.50
Debt Instrument, Interest Rate, Effective Percentage [Abstract]
Additional per annum interest margin (as a percent)	0.75%
Revolving credit facility | Base Rate | Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 2.50 or greater
Debt Instrument, Interest Rate, Effective Percentage [Abstract]
Additional per annum interest margin (as a percent)	1.00%
Revolving credit facility | Eurodollar Rate | Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: Less than 1.00
Debt Instrument, Interest Rate, Effective Percentage [Abstract]
Additional per annum interest margin (as a percent)	1.25%
Revolving credit facility | Eurodollar Rate | Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 1.00 to 1.75
Debt Instrument, Interest Rate, Effective Percentage [Abstract]
Additional per annum interest margin (as a percent)	1.50%
Revolving credit facility | Eurodollar Rate | Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 1.75 to 2.50
Debt Instrument, Interest Rate, Effective Percentage [Abstract]
Additional per annum interest margin (as a percent)	1.75%
Revolving credit facility | Eurodollar Rate | Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 2.50 or greater
Debt Instrument, Interest Rate, Effective Percentage [Abstract]
Additional per annum interest margin (as a percent)	2.00%
Amended senior revolving credit facility
Debt Obligations
Borrowing capacity	$ 577,500		600,000
Line of credit borrowing capacity accordion option	150,000
Payments on term loan	22,500
Term loan
Debt Obligations
Borrowing capacity	150,000
Outstanding balance	$ 127,500		135,000
Other disclosures
Weighted average interest rate (as a percent)	1.40%
Notes to former owners
Other disclosures
Cumulative number of companies acquired | item	5
Outstanding balance	$ 34,500		$ 31,000
Promissory note | Walker
Other disclosures
Outstanding balance	$ 10,000
Weighted average interest rate (as a percent)	4.00%
Promissory note | TAS Energy
Other disclosures
Outstanding balance	$ 8,000
Weighted average interest rate (as a percent)	3.50%
Promissory note | T E C Industrial Construction and Maintenance
Other disclosures
Outstanding balance	$ 7,000
Weighted average interest rate (as a percent)	2.50%
Promissory note | Electrical Contractor North Carolina
Other disclosures
Outstanding balance	$ 6,000
Weighted average interest rate (as a percent)	3.00%
Promissory note | Mechanical Contractor Utah
Other disclosures
Outstanding balance	$ 3,500
Weighted average interest rate (as a percent)	2.50%
Letter of Credit
Debt Obligations
Borrowing capacity	$ 160,000