Consolidated Statements Of Comprehensive Income - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Consolidated Statements Of Comprehensive Income [Abstract]
Net income		$ 73,170	$ 67,429	$ 184,533	$ 173,356
Other comprehensive income, net of tax:
Unrealized holding gain (loss) on investments, net of tax expense (benefit) of $11 and $(120) for the three months and $14 and $(90) for the nine months ended September 30, 2016 and 2015, respectively		20	(223)	26	(169)
Reclassification of gain on sale of investment to net income, net of tax of $30 for the nine months ended September 30, 2016	[1]			(57)
Comprehensive income		$ 73,190	$ 67,206	$ 184,502	$ 173,187

[1] Amount of pre-tax gain of $87 reclassified from accumulated other comprehensive income to gain on sale of other assets on the consolidated statements of net income for the nine months ended September 30, 2016.