Reconciliation of Earnings Per Share (Reconciliation) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Earnings Per Share Reconciliation
Net Income, Basic EPS	$ 84,093	$ (19,298)	$ 83,067	$ 56,692	$ 62,823	$ 2,046	$ 131,287	$ 57,406	$ 204,554	$ 253,562	$ 259,624
Basic Shares Outstanding (in shares)									72,317,865	72,119,021	72,055,661
Earnings Per Share, Basic (dollars per share)	$ 1.16	$ (0.27)	$ 1.15	$ 0.79	$ 0.87	$ 0.03	$ 1.82	$ 0.80	$ 2.83	$ 3.52	$ 3.60
Effect of dilutive securities
Net Income, Diluted EPS	$ 84,093	$ (19,298)	$ 83,067	$ 56,692	$ 62,823	$ 2,046	$ 131,287	$ 57,406	$ 204,554	$ 253,562	$ 259,624
Diluted Shares Outstanding (in shares)									72,470,622	72,316,214	72,332,369
Earnings Per Share, Diluted (dollars per share)	$ 1.15	$ (0.27)	$ 1.15	$ 0.78	$ 0.87	$ 0.03	$ 1.82	$ 0.79	$ 2.82	$ 3.51	$ 3.59
Stock options
Effect of dilutive securities
Incremental Common Shares Attributable to Share-based Payment Arrangements									112,000	196,000	270,000
Non-vested restricted stock
Effect of dilutive securities
Incremental Common Shares Attributable to Share-based Payment Arrangements									20,000	1,000	6,000
Performance share awards
Effect of dilutive securities
Incremental Common Shares Attributable to Share-based Payment Arrangements									21,000	0	0