Summary Of Significant Accounting And Reporting Policies (Schedule Of Earnings Per Share, Basic And Diluted) (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Accounting Policies [Abstract]
Numerator for both basic and diluted EPS, net income	$ 39,599,000	$ 41,877,000	$ 40,767,000	$ 46,345,000	$ 40,466,000	$ 43,397,000	$ 38,472,000	$ 42,333,000	$ 168,586,840	$ 164,668,228	$ 137,733,969
Denominator for basic EPS, weighted-average common shares outstanding									143,097,530	142,492,699	139,356,831
Potentially dilutive shares resulting from stock option plans									870,501	1,784,109	1,378,936
Denominator for diluted EPS									143,968,031	144,276,808	140,735,767