Consolidated Statements Of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Consolidated Statements Of Comprehensive Income [Abstract]
Unrealized gain (loss) on investments, tax expense (benefit)		$ 113	$ (93)
Unrealized (loss) gain, net of tax (benefit) expense	$ (5,304)	2,174	3,736
Reclassification adjustment for gains included in net income, tax expense	$ 224	$ 949	$ 5,853