Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Earnings Per Share) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended
Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Numerator:
Net income	$ 217,095us-gaap_NetIncomeLoss	$ 140,545us-gaap_NetIncomeLoss	$ 41,880us-gaap_NetIncomeLoss	$ 74,819us-gaap_NetIncomeLoss	$ 220,053us-gaap_NetIncomeLoss	$ 2,281,884us-gaap_NetIncomeLoss	$ 36,417us-gaap_NetIncomeLoss	$ 81,762us-gaap_NetIncomeLoss	$ 474,338us-gaap_NetIncomeLoss	$ 2,620,116us-gaap_NetIncomeLoss	$ 206,145us-gaap_NetIncomeLoss
Less: earnings distributed to participating securities									(583)	(407)	0
Less: undistributed earnings allocated to participating securities									(2,668)	(19,201)	0
Numerator for basic earnings per share									471,087	2,600,508	206,145
Add back: undistributed earnings allocated to participating securities									2,668	19,201	0
Less: undistributed earnings reallocated to participating securities									(2,643)us-gaap_UndistributedEarningsDiluted	(18,845)us-gaap_UndistributedEarningsDiluted	0us-gaap_UndistributedEarningsDiluted
Numerator for diluted earnings per share									$ 471,112	$ 2,600,864	$ 206,145
Denominator:
Basic shares outstanding	369,533	373,531	376,072	383,991	379,879	382,883	385,389	384,228	370,377	383,077	381,562
Effect of dilutive securities (shares)	3,734	3,761	3,592	3,815	3,845	3,220	5,791	6,093	3,725	3,789	3,002
Diluted shares outstanding (shares)	373,267	377,292	379,664	387,806	383,724	386,103	391,180	390,321	374,102	386,866	384,564
Earnings per share:
Basic (usd per share)	$ 0.58us-gaap_EarningsPerShareBasic	$ 0.37us-gaap_EarningsPerShareBasic	$ 0.11us-gaap_EarningsPerShareBasic	$ 0.19us-gaap_EarningsPerShareBasic	$ 0.58us-gaap_EarningsPerShareBasic	$ 5.92us-gaap_EarningsPerShareBasic	$ 0.09us-gaap_EarningsPerShareBasic	$ 0.21us-gaap_EarningsPerShareBasic	$ 1.27us-gaap_EarningsPerShareBasic	$ 6.79us-gaap_EarningsPerShareBasic	$ 0.54us-gaap_EarningsPerShareBasic
Diluted (usd per share)	$ 0.58us-gaap_EarningsPerShareDiluted	$ 0.37us-gaap_EarningsPerShareDiluted	$ 0.11us-gaap_EarningsPerShareDiluted	$ 0.19us-gaap_EarningsPerShareDiluted	$ 0.57us-gaap_EarningsPerShareDiluted	$ 5.87us-gaap_EarningsPerShareDiluted	$ 0.09us-gaap_EarningsPerShareDiluted	$ 0.21us-gaap_EarningsPerShareDiluted	$ 1.26us-gaap_EarningsPerShareDiluted	$ 6.72us-gaap_EarningsPerShareDiluted	$ 0.54us-gaap_EarningsPerShareDiluted

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