CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Realized losses on short-term investments reclassified from accumulated other comprehensive income, net of tax of $0, ($1), $0 and ($2), respectively	$ 0	$ (1)	$ 0	$ (2)
Net change in unrealized gains on available-for-sale investments, net of tax of $136, ($1,242), $272 and ($1,802), respectively	$ 136	$ (1,242)	$ 272	$ (1,802)