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, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Numerators:
Numerator for both basic and diluted EPS, net income	$ 88,396,000	$ 78,332,000	$ 74,558,000	$ 77,183,000	$ 70,975,000	$ 72,337,000	$ 76,727,000	$ 68,566,000	$ 318,469,859	$ 288,604,579	$ 222,929,949
Denominators:
Denominator for basic EPS, weighted-average common shares outstanding									293,096,212	290,952,123	286,920,036
Potentially dilutive shares resulting from stock option plans									3,141,687	3,347,236	1,628,306
Denominator for diluted EPS									296,237,899	294,299,359	288,548,342