Summary of Significant Accounting Policies - Trade Accounts Receivable (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounting Policies [Abstract]
Bad debt expense, net of recoveries	$ (31)	$ 167	$ (40)

Amount of increase (decrease) in the allowance for doubtful accounts.

No definition available.

Name:	us-gaap_AllowanceForDoubtfulAccountsReceivablePeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration