Merger with Deltic (Summary of Revenue and Income Before Income Taxes From Acquired Deltic Operations) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Business Acquisition [Line Items]
Net sales	$ 268,233	$ 163,229	$ 468,130	$ 312,910
Income before income taxes	58,153	$ 33,425	78,467	$ 52,364
Deltic [Member]
Business Acquisition [Line Items]
Net sales	80,053		108,859
Income before income taxes	$ 16,724		$ 7,613