Commitments and Contingencies - Additional Information (details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Loss Contingencies [Line Items]
Long-term liability for remediation and reclamation obligations	$ 1.5	$ 1.9
Term of obligation	5 years
Western Gas Partners [Member]
Loss Contingencies [Line Items]
Committed capital	64.1
Rent expense associated with office, warehouse and equipment leases	$ 3.5	$ 2.8	$ 3.0