Summary of Significant Accounting Policies, Earnings Per Average Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Accounting Policies [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount										0	0
INCOME
Income from continuing operations									$ 160,685	$ 163,648	$ 195,848
Deduct: non-participating stock dividends (4.5% preferred stock)									0	0	26
Deduct: non-participating stock redemption costs (4.5% preferred stock)									0	0	112
Net income applicable to common stock	25,112	66,407	42,032	27,133	23,112	63,818	46,686	30,031	160,685	163,648	195,710
Diluted net income applicable to common stock									$ 160,685	$ 163,648	$ 195,710
SHARES
Average number of basic common shares outstanding (in shares)									60,434,510	60,370,588	60,488,740
Effect of dilutive securities
Add: stock option grants (in shares)									0	4,154	20,647
Add: restricted stock (LTICP) (in shares)									285,580	253,387	324,177
Average number of diluted common shares outstanding (in shares)									60,720,090	60,628,129	60,833,564
PER SHARE AMOUNT
Net income applicable to common stock (in dollars per share)	$ 0.42	$ 1.10	$ 0.70	$ 0.45	$ 0.38	$ 1.06	$ 0.77	$ 0.50	$ 2.66	$ 2.71	$ 3.24
Diluted net income per average common share (in dollars per share)	$ 0.41	$ 1.09	$ 0.69	$ 0.45	$ 0.38	$ 1.05	$ 0.77	$ 0.50	$ 2.65	$ 2.70	$ 3.22