Nature of Operations and Summary of Significant Accounting Policies--Accounts Receivable (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
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
Receivables [Abstract]
Joint interests	$ 30,648	$ 31,335
Accrued commodity sales	45,667	60,768
Derivative settlements	19,678	4,616
Production tax receivable	2,031	694
Other	707	698
Allowance for doubtful accounts	(287)	(1,596)
Accounts receivable, net	$ 98,444	$ 96,515