Goodwill and Other Intangible Assets Goodwill and Other Intangible Assets - Allocation of purchase price to fair value of assets acquired and liabilities assumed (Details) (Credo [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012
Credo [Member]
Business Acquisition [Line Items]
Cash and short-term investments	$ 2,300		$ 2,300
Measurement period adjustment, cash and short-term investments	0
Receivables	10,147		9,144
Measurement period adjustment, receivables	1,003	[1]
Oil and gas properties and equipment	135,802		140,514
Measurement period adjustment, oil and gas properties and equipment	(4,712)	[2]
Other properties and equipment	67		67
Measurement period adjustment, other properties and equipment	0
Goodwill and other intangible assets	61,209		58,396
Measurement period adjustment, goodwill and other intangible assets	2,813	[3]
Other	676		676
Measurement period adjustment, other	0
Total assets acquired	210,201		211,097
Measurement period adjustment, total assets acquired	(896)
Accounts payable and accrued liabilities	29,940		29,927
Measurement period adjustment, accounts payable and accrued liabilities	13	[4]
Deferred tax liability	23,791		24,700
Measurement period adjustment, deferred tax liability	(909)	[5]
Other liabilities	1,255		1,255
Measurement period adjustment, other liabilities	0
Total liabilities assumed	54,986		55,882
Measurement period adjustment, total liabilities assumed	(896)
Estimated fair value of net assets acquired	155,215		155,215
Measurement period adjustment, estimated fair value of net assets acquired	$ 0

[1] Primarily related to unrecorded seismic and leasehold costs due from partners.

[2] Fair value adjustments allocated to near-term expiring leasehold acreage.

[3] Goodwill adjustments associated with fair value adjustments for oil and gas properties, net of deferred taxes and working capital adjustments.

[4] Primarily related to current income taxes payable.

[5] Primarily related to deferred taxes on fair value adjustments of near-term expiring leasehold acreage.