CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Change in fair value investments, tax	$ 57	$ 128	$ 1	$ 359

Other Comprehensive Income Unrealized Gain Loss In Fair Value Of Investments Tax

No definition available.

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Namespace Prefix:	xec_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration