Cash flow information (Details 1) - USD ($)		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016
Interest, net of amount capitalized and AFUDC - borrowed of $418 and $548 in 2017 and 2016, respectively		$ 39,207,000	$ 44,860,000
Income taxes paid, net	[1]	32,388,000	29,891,000
Property, plant and equipment additions in accounts payable		10,449,000	18,449,000
Capitalized interest and AFUDC borrowed		418,000	548,000
Continuing and discontinued operations [Member]
Income taxes paid, net		$ (3,600,000)	$ (500,000)

[1] Income taxes refunded, net of discontinued operations, were $(3.6) million and $(500,000) for the six months ended June 30, 2017 and 2016, respectively.