Nature of Operations and Summary of Significant Accounting Policies--Accounts Receivable (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Accounting Policies [Abstract]
Period within which joint interest accounts receivable are due	30 days
Period within which joint interest accounts receivable are past due	60 days
Bad debt expense	$ 498	$ 731	$ 179
Receivables [Abstract]
Joint interests	31,335	19,282
Accrued commodity sales	60,768	50,814
Derivative settlements	4,616	8,013
Other	1,392	472
Allowance for doubtful accounts	(1,596)	(1,274)
Accounts receivable, net	$ 96,515	$ 77,307