Earnings Per Common Share (Details) - Basic and Diluted Earnings Per Common Share (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Earnings Per Share, Basic and Diluted [Abstract]
Net income	$ 18,549		$ 29,323		$ 54,713		$ 60,141
Net income applicable to non-vested restricted shares	(242)		(416)		(697)		(847)
Net income applicable to common shares	$ 18,307		$ 28,907		$ 54,016		$ 59,294
Weighted-average common shares outstanding (in Shares)	74,341		74,023		74,270		73,969
Dilutive effect of common stock equivalents (in Shares)	11		11		12		9
Weighted-average diluted common shares outstanding (in Shares)	74,352		74,034		74,282		73,978
Basic earnings per common share (in Dollars per share)	$ 0.25		$ 0.39		$ 0.73		$ 0.80
Diluted earnings per common share (in Dollars per share)	$ 0.25		$ 0.39		$ 0.73		$ 0.80
Anti-dilutive shares not included in the computation of diluted earnings per common share (in thousands)	1,155	[1]	1,412	[1]	1,215	[1]	1,483	[1]

[1] This amount represents outstanding stock options for which the exercise price is greater than the average market price of the Company's common stock.