Summary Of Significant Accounting Policies (Schedule Of Error Corrections And Prior Period Adjustments) (Details) - USD ($) $ / shares in Units, $ in Thousands	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, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Prepaid expenses and other assets	$ 31,351				$ 29,018								$ 31,351	$ 29,018
Income taxes payable	5,069				5,450								5,069	5,450
Retained earnings	704,905				644,085								704,905	644,085
Other expense													(1,141)	(1,673)	$ (315)
Income tax expense													(5,362)	17,388	5,018
Net income	$ 39,421	$ 20,565	$ 21,210	$ 14,205	$ 23,338	$ 16,906	$ 21,558	$ 19,439	$ 67,710	$ 23,648	$ 8,256	$ 11,331	$ 95,401	$ 81,241	$ 110,945
Basic earnings per share	$ 0.78	$ 0.4	$ 0.41	$ 0.27	$ 0.44	$ 0.32	$ 0.4	$ 0.36	$ 1.26	$ 0.44	$ 0.15	$ 0.21	$ 1.85	$ 1.52	$ 2.05
Diluted earnings per share	$ 0.77	$ 0.4	$ 0.4	$ 0.27	$ 0.44	$ 0.31	$ 0.4	$ 0.36	$ 1.25	$ 0.43	$ 0.15	$ 0.21	$ 1.83	$ 1.5	$ 2.03
Net cash provided by operations													$ 146,804	$ 135,440	$ 98,863
Effect of exchange rate changes													(1,021)	(1,262)	938
As Previously Reported [Member]
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Prepaid expenses and other assets					$ 30,453									30,453
Income taxes payable	$ 5,470				5,470								5,470	5,470
Retained earnings	645,500				645,500								645,500	645,500
Other expense														(452)	(101)
Income tax expense														17,408	5,018
Net income														$ 82,442	$ 111,159
Basic earnings per share														$ 1.54	$ 2.05
Diluted earnings per share														$ 1.52	$ 2.03
Net cash provided by operations														$ 136,601	$ 99,077
Effect of exchange rate changes														(2,483)	724
As Revised [Member}
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Prepaid expenses and other assets					29,018									29,018
Income taxes payable	5,450				5,450								5,450	5,450
Retained earnings	$ 644,085				$ 644,085								$ 644,085	644,085
Other expense														(1,673)	(315)
Income tax expense														17,388	5,018
Net income														$ 81,241	$ 110,945
Basic earnings per share														$ 1.52	$ 2.05
Diluted earnings per share														$ 1.5	$ 2.03
Net cash provided by operations														$ 135,440	$ 98,863
Effect of exchange rate changes														$ (1,262)	$ 938