Fair Value Measurements (Narratives) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Interest expense	$ 8,377	$ 6,551	$ 4,378
Lb Pipe Coupling Products Llc
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Impairment of long lived assets to be disposed of	413
Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Notional amount	50,000
Interest expense	$ 378