Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
	Jan. 01, 2016	Mar. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Use of Estimates
Gain Loss From Project			$ 3,400		$ 3,400	$ 4,400
Cash paid for:
Interest				$ 1,864	1,408	1,764
Income taxes paid				$ 29,349	35,538	15,366
Revenue Recognition
Percentage of revenue earned on a project basis				82.00%
Contracts in progress
Costs incurred on contracts in progress			1,135,279	$ 1,116,182	1,135,279
Estimated earnings, net of losses			188,243	207,252	188,243
Less-Billings to date			1,377,581	1,378,050	1,377,581
Contracts in progress			(54,059)	(54,616)	(54,059)
Costs and estimated earnings in excess of billings			31,338	29,369	31,338
Billings in excess of costs and estimated earnings			85,397	$ 83,985	85,397
Period during which progress billings or contract price can be withheld until completion of work				6 months
Retention receivable			51,600	$ 60,700	51,600
Retention payable			7,800	$ 10,100	7,800
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
Deferred tax liabilities			$ 1,810	$ 2,289	1,810
Effect of share-based compensation of excess tax benefit in provision for income taxes				1,900	2,100	1,800
Impact on retained earnings for minimum statutory withholding tax requirement due to amendments				$ 1,304	937	531
Excess tax benefit of stock-based compensation					$ 1,240	$ 115
Accounting Standards Update 2016-09 | Adjustments for New Accounting Principle, Early Adoption
Recent Accounting Pronouncements
Effect of share-based compensation of excess tax benefit in provision for income taxes	$ 100
Excess tax benefit of stock-based compensation, operating activities		$ 100
Excess tax benefit of stock-based compensation		$ (100)
Accounting Standards Update 2016-09 | Adjustments for New Accounting Principle, Early Adoption | Maximum
Recent Accounting Pronouncements
Cumulative effect adjustment to retained earnings for increase to stock compensation expense	$ 100