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, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerators:
Numerator for both basic and diluted EPS, net income	$ 88,761,000	$ 92,065,000	$ 86,485,000	$ 80,280,000	$ 88,396,000	$ 78,332,000	$ 74,558,000	$ 77,183,000	$ 347,591,276	$ 318,469,859	$ 288,604,579
Denominators:
Denominator for basic EPS, weighted-average common shares outstanding (in shares)									288,433,772	293,096,212	290,952,123
Potentially dilutive shares resulting from stock option plans (in shares)									2,638,544	3,141,687	3,347,236
Denominator for diluted EPS (in shares)									291,072,316	296,237,899	294,299,359