Merger, Integration and Other Costs (Summary of Merger and Restructuring Costs) (Details) - USD ($) $ in Thousands		3 Months Ended	6 Months Ended
		Jun. 30, 2018	Jun. 30, 2018
Merger Integration And Other Costs [Abstract]
Merger costs		$ 362	$ 10,623
Restructuring costs:
Termination benefits		224	8,782
Professional services		353	655
Other		79	213
Total restructuring costs		656	9,650
Total merger and restructuring costs	[1]	$ 1,018	$ 20,273

[1] For integration and restructuring costs related to the merger with Deltic see Note 14: Merger, Integration and Other Costs.