CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement Of Stockholders Equity [Abstract]
Tax benefit from AFS securities adjustment	[1]	$ 1,486	$ 1,369	$ 916

[1] Represents change in fair value of available for sale investments, net of tax benefit of $1,486 thousand, $1,369 thousand and $916 thousand in years ended December 31, 2016, 2015 and 2014, respectively.