Consolidated Financial Statements (Immaterial Adjustments to Prior Interim Periods) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended	9 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Jun. 30, 2016	Sep. 30, 2016	Sep. 30, 2015
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Sales	$ 272,734	$ 265,738	$ 237,671	$ 304,994	$ 503,409	$ 776,143	$ 758,780
Gross profit	67,887	68,843	54,150	61,396	122,993	190,880	135,430
Income from operations	26,363	28,416	17,601	23,394	46,017	72,380	43,565
Income from continuing operations	13,786	16,715	14,105	13,632	30,820	41,427	23,256
Provision for income taxes	8,952	(1,897)	5,076	7,664	3,179	12,131	13,158
Net income	$ 13,786	$ 18,612	$ 9,029	$ 13,632	$ 27,641	$ 41,427	$ 23,228
Net earnings per share - Basic (in USD per share)	$ 0.44	$ 0.59	$ 0.29	$ 0.44	$ 0.88	$ 1.32	$ 0.74
Net earnings per share - Diluted (in USD per share)	$ 0.43	$ 0.58	$ 0.28	$ 0.43	$ 0.87	$ 1.29	$ 0.74
Revenue Recognition Related to Percentage of Completion Method of Accounting | As Previously Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Sales		$ 263,099	$ 233,677		$ 496,776
Gross profit		66,204	50,156		116,360
Income from operations		25,777	13,607		39,384
Income from continuing operations		14,076	10,111		24,187
Provision for income taxes		(2,913)	3,618		705
Net income		$ 16,989	$ 6,493		$ 23,482
Net earnings per share - Basic (in USD per share)		$ 0.54	$ 0.21		$ 0.75
Net earnings per share - Diluted (in USD per share)		$ 0.53	$ 0.20		$ 0.74
Revenue Recognition Related to Percentage of Completion Method of Accounting | Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Sales		$ 2,639	$ 3,994		$ 6,633
Gross profit		2,639	3,994		6,633
Income from operations		2,639	3,994		6,633
Income from continuing operations		2,639	3,994		6,633
Provision for income taxes		1,016	1,458		2,474
Net income		$ 1,623	$ 2,536		$ 4,159
Net earnings per share - Basic (in USD per share)		$ 0.05	$ 0.08		$ 0.13
Net earnings per share - Diluted (in USD per share)		$ 0.05	$ 0.08		$ 0.13
Renewable Energy and Conservation
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Sales		$ 64,766	$ 57,874		$ 122,640
Income from operations		10,296	8,307		18,603
Renewable Energy and Conservation | Revenue Recognition Related to Percentage of Completion Method of Accounting | As Previously Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Sales		62,127	53,880		116,007
Income from operations		7,657	4,313		11,970
Renewable Energy and Conservation | Revenue Recognition Related to Percentage of Completion Method of Accounting | Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Sales		2,639	3,994		6,633
Income from operations		$ 2,639	$ 3,994		$ 6,633