Commitments and Contingencies (Class Action Litigation) (Details) - lawsuit	1 Months Ended		35 Months Ended
	Jan. 31, 2016	Nov. 30, 2015	Dec. 31, 2018
Lawsuits Filed in the United States District Court for the Southern District of Texas
Loss Contingencies [Line Items]
Number of lawsuits filed	1	4
Derivative Lawsuit Against Officers and Directors
Loss Contingencies [Line Items]
Number of lawsuits filed	3
Derivative Lawsuit Filed in District Court of Harris County, Texas
Loss Contingencies [Line Items]
Number of lawsuits filed	2		1