Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended													12 Months Ended
	Dec. 31, 2015	[1]	Sep. 30, 2015	[1]	Jun. 30, 2015	[1]	Mar. 31, 2015	[1]	Dec. 31, 2014		Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income (Numerator)
Income available to common stockholders, Basic														$ 74,479	$ 177,949	$ 112,143
Income available to common stockholders after assumed conversions, Diluted														$ 74,479	$ 177,949	$ 112,143
Weighted Shares (Denominator)
Weighted shares, basic (in shares)														55,157	55,008	54,947
Weighted shares, diluted (in shares)														55,209	55,020	54,964
Earnings Per Share Basic and Diluted, Per Share Amounts [Abstract]
Basic (in dollars per share)	$ 0.42		$ 0.28		$ 0.17		$ 0.47		$ (0.38)		$ 0.57	$ 1.73	$ 1.32	$ 1.35	$ 3.23	$ 2.04
Diluted (in dollars per share)	$ 0.42		$ 0.28		$ 0.17		$ 0.47		$ (0.38)	[1]	$ 0.57	$ 1.73	$ 1.32	$ 1.35	$ 3.23	$ 2.04
Common Stock [Member]
Earnings Per Share Basic and Diluted, Per Share Amounts [Abstract]
Potentially dilutive securities (in shares)														67	252	359
Stock Options [Member]
Income (Numerator)
Effect of dilutive securities: Options														$ 0	$ 0	$ 0
Weighted Shares (Denominator)
Effect of dilutive securities: options (in shares)														15	12	17
Restricted Stock Units (RSUs) [Member]
Income (Numerator)
Effect of dilutive securities: Options														$ 0	$ 0	$ 0
Weighted Shares (Denominator)
Effect of dilutive securities: options (in shares)														37	0	0

[1] The basic and diluted earnings per share do not sum due to rounding.