Consolidated Statements Of Comprehensive Income - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Consolidated Statements Of Comprehensive Income [Abstract]
Net income		$ 49,072	$ 51,737
Other comprehensive income, net of tax:
Unrealized holding gain (loss) on investments, net of tax expense (benefit) of $31 and $(4) for the three months ended March 31, 2017 and 2016, respectively		58	(6)
Reclassification of gain on sale of investment to net income, net of tax of $30 for the three months ended March 31, 2016	[1]		(57)
Comprehensive income		$ 49,130	$ 51,674

[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 three months ended March 31, 2016.