CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - 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]
Net income	$ 5,486	$ 16,251	$ 9,128	$ 18,616
Other comprehensive income:
Realized losses on short-term investments reclassified from accumulated other comprehensive income, net of tax of $0, ($1), $0 and ($2), respectively	0	0	0	3
Net change in unrealized gains on available-for-sale investments, net of tax of $136, ($1,242), $272 and ($1,802), respectively	35	133	211	2,518
Comprehensive income	$ 5,521	$ 16,384	$ 9,339	$ 21,137