Consolidated Statements Of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Consolidated Statements Of Comprehensive Income [Abstract]
Net income attributable to common shareholders	$ 48,545		$ 42,859
Other comprehensive income, net of tax:
Unrealized holding gain on investments, net of tax expense of $41 and $38 for the three months ended March 31, 2015 and 2014, respectively	75		72
Reclassification adjustment for loss reported in net income, net of tax benefit of $134 for the three months ended March 31, 2014		[1]	249	[1]
Comprehensive income	$ 48,620		$ 43,180

[1] Amount of pre-tax loss of $383 reclassified from accumulated other comprehensive income to loss on sale of other assets on the consolidated statements of net income for the three months ended March 31, 2014