Note 7 - Segment Reporting - Net Sales by Products and Services (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net sales	$ 590,932	$ 601,135	$ 541,916	$ 470,353	$ 563,404	$ 562,388	$ 497,581	$ 400,091	$ 2,204,336	$ 2,023,464	$ 1,679,373
Residential Power Products [Member]
Net sales									1,143,723	1,042,739	870,490
Commercial and Industrial Power Products [Member]
Net sales									871,595	820,270	684,353
Other Products and Services [Member]
Net sales									189,018	160,455	124,530
Domestic [Member]
Net sales									1,742,898	1,566,520	1,271,678
Domestic [Member] | Residential Power Products [Member]
Net sales									1,086,019	980,707	796,237
Domestic [Member] | Commercial and Industrial Power Products [Member]
Net sales									513,482	461,415	372,635
Domestic [Member] | Other Products and Services [Member]
Net sales									143,397	124,398	102,806
International [Member]
Net sales									461,438	456,944	407,695
International [Member] | Residential Power Products [Member]
Net sales									57,704	62,032	74,253
International [Member] | Commercial and Industrial Power Products [Member]
Net sales									358,113	358,855	311,718
International [Member] | Other Products and Services [Member]
Net sales									$ 45,621	$ 36,057	$ 21,724