Summary of Significant Accounting Policies, Earnings Per Average Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income
Basic net income applicable to common stock	$ 70,835	$ 66,407	$ 133,392	$ 135,572
Diluted net income applicable to common stock	$ 70,835	$ 66,407	$ 133,392	$ 135,572
Shares
Average number of basic common shares outstanding (in shares)	60,372,569	60,450,384	60,410,122	60,428,944
Effect of dilutive securities
Add: restricted stock (LITCP) (in shares)	317,027	298,263	301,421	265,688
Average number of diluted common shares outstanding (in shares)	60,689,596	60,748,647	60,711,543	60,694,632
Per Share Amount
Net income applicable to common stock (in dollars per share)	$ 1.17	$ 1.10	$ 2.21	$ 2.25
Diluted net income per average common share (in dollars per share)	$ 1.17	$ 1.09	$ 2.20	$ 2.23
Stock option grants during period (in shares)			0	0