Revenue Recognition (Disaggregated Net Sales) (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) unit	Sep. 30, 2017 USD ($) unit	Sep. 30, 2018 USD ($) unit	Sep. 30, 2017 USD ($) unit
Disaggregation of Revenue [Line Items]
Net Sales	$ 112,937	$ 113,668	$ 321,607	$ 301,072
Rooftop Units
Disaggregation of Revenue [Line Items]
Net Sales	$ 86,498	$ 88,012	$ 244,978	$ 235,676
Total Units | unit	4,053,000	4,538,000	11,696,000	12,185,000
Condensing Units
Disaggregation of Revenue [Line Items]
Net Sales	$ 5,356	$ 5,230	$ 14,492	$ 14,662
Total Units | unit	611,000	496,000	1,647,000	1,715,000
Air Handlers
Disaggregation of Revenue [Line Items]
Net Sales	$ 5,686	$ 5,339	$ 17,479	$ 16,728
Total Units | unit	713,000	593,000	2,067,000	1,916,000
Outdoor Mechanical Rooms
Disaggregation of Revenue [Line Items]
Net Sales	$ 311	$ 899	$ 2,178	$ 2,641
Total Units | unit	8,000	17,000	35,000	56,000
Water Source Heat Pumps
Disaggregation of Revenue [Line Items]
Net Sales	$ 3,112	$ 3,027	$ 10,240	$ 6,726
Total Units | unit	1,162,000	614,000	3,780,000	1,510,000
Other
Disaggregation of Revenue [Line Items]
Net Sales	$ 11,974	$ 11,161	$ 32,240	$ 24,639
Total Units | unit	6,547,000	6,258,000	19,225,000	17,382,000