Note 3 - Acquisitions - Unaudited Pro Forma Information (Details) - USD ($) $ / shares in Units, $ 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
As reported	$ 69,614	$ 75,574	$ 61,958	$ 44,861	$ 75,575	$ 75,776	$ 53,261	$ 33,645	$ 252,007	$ 238,257	$ 157,808
Net income attributable to common shareholders per common share - diluted: (in dollars per share)	$ 1.12	$ 1.18	$ 0.98	$ 0.76	$ 1.20	$ 1.11	$ 0.82	$ 0.42	$ 4.03	$ 3.54	$ 2.53
Pro Forma [Member]
Net sales									$ 2,206,952	$ 2,067,737	$ 1,755,358
As reported									$ 248,335	$ 230,379	$ 151,764
Net income attributable to common shareholders per common share - diluted: (in dollars per share)									$ 3.97	$ 3.41	$ 2.44