Commitments and Contingencies Self-Insurance (Details) $ in Millions	Mar. 31, 2017 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Self insurance Workers' Comp Coverage Ceiling per accident	$ 1.0
Self Insurance General Liability Claims Coverage Ceiling per occurence	4.0
Self Insurance Auto Liabiity Coverage Ceiling per accident	$ 4.0

Self Insurance General Liability Claims Coverage Ceiling per occurence

No definition available.

Name:	dk_SelfInsuranceGeneralLiabilityClaimsCoverageCeilingPerOccurence
Namespace Prefix:	dk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant