Share-Based Compensation (Details Textual) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Stock option activity in shares and weighted average price
Options outstanding, beginning of period, shares			1,488,314
Options outstanding, beginning of period, weighted average price			$ 33.38
Options granted, shares			0
Options granted, weighted average price			$ 0.00
Options canceled, shares			(58,694)
Options canceled, weighted average price			$ 23.24
Options exercised, shares			0
Options exercised, weighted average price			$ 0.00
Options outstanding, end of period, shares	1,429,620		1,429,620
Options oustanding, end of period, weighted average price	$ 33.78		$ 33.78
Options exercisable, end of period, shares	1,327,449		1,327,449
Options exercisable, end of period, weighted average price	$ 33.87		$ 33.87
Share-based Compensation Arrangement, Additional General Disclosures [Abstract]
Tax shortfall in earnings related to share-based compensation	$ 200,000		$ 1,900,000
Stock-based compensation expenses			3,683,000	6,018,000
Share-based compensation (capitalized)	900,000	1,600,000	2,000,000	3,200,000
Remaining contract life of outstanding stock options.			5 years 0 months
Remaining contract life of exercisable stock option			4 years 10 months
General and Administrative Expense [Member]
Share-based Compensation Arrangement, Additional General Disclosures [Abstract]
Stock-based compensation expenses	1,700,000	2,800,000	3,300,000	5,600,000
Lease Operating Cost [Member]
Share-based Compensation Arrangement, Additional General Disclosures [Abstract]
Stock-based compensation expenses	100,000	100,000	100,000	200,000
Employee Stock Option [Member]
Share-based Compensation Arrangement, Additional General Disclosures [Abstract]
Unrecognized compensation cost for stock grants	300,000		300,000
Weighted average remaining recognition period of cost for stock grants			7 months
Restricted Stock Awards [Member]
Restricted stock activity
Restricted shares outstanding, beginning of period, shares			1,267,110
Restricted shares outstanding, beginning of period, weighted average price			$ 21.54
Restricted shares granted, weighted average price			$ 11.57
Restricted shares granted, shares			716,650
Restricted shares canceled, weighted average price			$ 15.37
Restricted shares canceled, shares			(114,672)
Restricted shares vested, weighted average price			$ 34.83
Restricted shares vested, shares			(291,561)
Restricted shares outstanding, end of period, weighted average price	$ 15.00		$ 15.00
Restricted shares outstanding, end of period, shares	1,577,527		1,577,527
Share-based Compensation Arrangement, Additional General Disclosures [Abstract]
Unrecognized compensation cost for stock grants	14,900,000		14,900,000
Weighted average remaining recognition period of cost for stock grants			1 year 11 months
Grant date fair value of shares vested			10,200,000
Restricted Stock Units (RSUs) [Member]
Restricted stock activity
Restricted shares outstanding, beginning of period, shares			189,700
Restricted shares outstanding, beginning of period, weighted average price			$ 15.01
Restricted shares granted, weighted average price			$ 11.68	$ 15.01
Restricted shares granted, shares			185,250	189,700
Restricted shares canceled, weighted average price			$ 0.00
Restricted shares canceled, shares			0
Restricted shares vested, weighted average price			$ 0.00
Restricted shares vested, shares			0
Restricted shares outstanding, end of period, weighted average price	$ 13.36		$ 13.36
Restricted shares outstanding, end of period, shares	374,950		374,950
Share-based Compensation Arrangement, Additional General Disclosures [Abstract]
Unrecognized compensation cost for stock grants	$ 3,100,000		$ 3,100,000
Weighted average remaining recognition period of cost for stock grants			2 years 4 months
Restricted Stock Awards Vesting Term			3 years 1 month
Minimum [Member]
Share-based Compensation Arrangement, Additional General Disclosures [Abstract]
Restricted Stock Awards Vesting Term			1 year
Percent of payout for performance based restricted stock unit grants			0.00%
Maximum Payout [Member]
Share-based Compensation Arrangement, Additional General Disclosures [Abstract]
Restricted Stock Awards Vesting Term			3 years
Percent of payout for performance based restricted stock unit grants			200.00%
Target Payout [Member]
Share-based Compensation Arrangement, Additional General Disclosures [Abstract]
Percent of payout for performance based restricted stock unit grants			100.00%