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, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Numerators:
Numerator for both basic and diluted EPS, net income	$ 70,975,000	$ 72,337,000	$ 76,727,000	$ 68,566,000	$ 69,881,000	$ 55,521,000	$ 52,097,000	$ 45,431,000	$ 288,604,579	$ 222,929,949	$ 168,586,840
Denominators:
Denominator for basic EPS, weighted-average common shares outstanding									290,952,123	286,920,036	286,195,060
Potentially dilutive shares resulting from stock option plans									3,347,236	1,628,306	1,741,002
Denominator for diluted EPS									294,299,359	288,548,342	287,936,062