Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Basic and Diluted Earnings Per Share
Net income available to common stockholders, basic and diluted	$ 26,730	$ 20,768
Average outstanding shares - basic	74,437,393	71,965,665
Add: dilutive stock options and awards	43,425	47,512
Average outstanding shares - diluted	74,480,818	72,013,177
Basic earnings per share	$ 0.36	$ 0.29
Diluted earnings per share	$ 0.36	$ 0.29
Earnings Per Share
Options excluded from the diluted average outstanding share calculation	0	152,559