Summary of Significant Accounting Policies, Earnings Per Average Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Income
Basic net income applicable to common stock	$ 25,924	$ 27,133
Diluted net income applicable to common stock	$ 25,924	$ 27,133
Shares
Average number of basic common shares outstanding (in shares)	60,472,969	60,399,697
Effect of dilutive securities
Add: restricted stock (LTICP) (in shares)	240,618	267,704
Average number of diluted common shares outstanding (in shares)	60,713,587	60,667,401
Per Share Amount
Net income applicable to common stock (in dollars per share)	$ 0.43	$ 0.45
Diluted net income per average common share (in dollars per share)	$ 0.43	$ 0.45
Stock Options [Member]
Per Share Amount
Amount of stock options excluded from computation of diluted earnings per share (in shares)	0	0