Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Earnings Per Share [Abstract]
Net income for basic and diluted earnings per share (in dollars)	$ 26,457	$ 76,226
Weighted-average common shares outstanding	221,295	219,097
Dilutive effect of stock options, performance share awards and restricted stock awards (in shares)	1,376	1,387
Diluted weighted-average shares outstanding	222,671	220,484
Basic earnings per share (in dollars per share)	$ 0.12	$ 0.35
Diluted earnings per share (in dollars per share)	$ 0.12	$ 0.35