Summary of Significant Accounting Policies (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) location
Use of Estimates
Number or operating locations | location			2
Gain Loss From Project			$ 3,400
Cash paid for:
Interest	$ 2,832	$ 1,864	1,408
Income taxes paid	$ 38,144	29,349	35,538
Revenue Recognition
Percentage of revenue earned on a project basis	81.00%
Contracts in progress
Costs incurred on contracts in progress	$ 1,288,330	1,116,182
Estimated earnings, net of losses	253,641	207,252
Less-Billings to date	(1,617,860)	(1,378,050)
Contracts in progress	(75,889)	(54,616)
Costs and estimated earnings in excess of billings	30,116	29,369
Billings in excess of costs and estimated earnings	$ 106,005	83,985
Period during which progress billings or contract price can be withheld until completion of work	6 months
Retention receivable	$ 68,700	60,700
Retention payable	$ 11,900	10,100
Warranty Costs
Labor warranty period after servicing of existing HVAC system	30 days
Income Taxes
Federal statutory income taxes rate (as a percent)	35.00%
Recent Accounting Pronouncements
Material impact on consolidated financial statements due to adoption of ASU 2014-09	$ 168,269	123,984
Deferred tax liabilities	2,263	2,289
Effect of share-based compensation of excess tax benefit in provision for income taxes	2,400	1,900	2,100
Impact on retained earnings for minimum statutory withholding tax requirement due to amendments	1,419	$ 1,304	937
Excess tax benefit of stock-based compensation			$ 1,240
Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606
Recent Accounting Pronouncements
Material impact on consolidated financial statements due to	$ 500