Summary of Significant Accounting Policies - Additional Information 4 (Detail) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013 Customer Unit	Dec. 31, 2012 Customer	Dec. 31, 2011 Customer
Operations And Summary Of Significant Accounting Policies [Line Items]
Number of major customers of oil and gas sales	2	2	2
General and administrative expenses reimbursements of overhead costs	$ 11.9	$ 11.5	$ 10.5
Interest costs, capitalized during period	$ 4.7	$ 20.9	$ 13.2
Performance multiplier, minimum	0
Performance multiplier, maximum	3
Restricted Stock
Operations And Summary Of Significant Accounting Policies [Line Items]
Shares of unvested restricted stock outstanding	1,515,889	1,960,835	2,114,520
Major Purchaser One
Operations And Summary Of Significant Accounting Policies [Line Items]
Percentage accounted of oil and gas sales	51.00%	42.00%	49.00%
Major Purchaser Two
Operations And Summary Of Significant Accounting Policies [Line Items]
Percentage accounted of oil and gas sales	36.00%	27.00%	14.00%