Earnings Per Share (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 [Line Items]
Income available to common stockholders, Basic											$ 112,143	$ 116,911	$ 191,164
Effect of dilutive securities: Options											0	0	0
Income available to common stockholders after assumed conversions, Diluted											$ 112,143	$ 116,911	$ 191,164
Weighted Shares, Basic											54,947,000	54,899,000	54,825,000
Effect of dilutive securities: Options											17,000	23,000	20,000
Weighted Shares, Diluted											54,964,000	54,922,000	54,845,000
Per-Share Amount, Basic	$ 0.28	$ 0.72	$ (0.17)		$ 1.21	$ (0.32)	$ 1.21		$ (0.10)	$ 1.34	$ 2.04	$ 2.13	$ 3.49
Per-Share Amount, Diluted	$ 0.28	$ 0.72	$ (0.17)	[1]	$ 1.21	$ (0.32)	$ 1.21	[1]	$ (0.10)	$ 1.34	$ 2.04	$ 2.13	$ 3.49
Potentially dilutive securities (in shares)											421,000	415,000	504,000
Common Stock [Member]
Earnings Per Share [Line Items]
Potentially dilutive securities (in shares)											63,000	80,000	103,000

[1] The dilutive impact of incremental shares is excluded from net loss position in accordance with GAAP.