CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
NET INCOME	$ 10,365	$ 1,949
OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX:
Unrealized loss on available-for-sale securities, net of tax of $8 and $82, respectively	(15)	(151)
Employee benefit plan:
Actuarial gain (loss), net of tax of none and $469, respectively		(834)
Amortization of prior service cost and actuarial loss for retirement plan included in net periodic pension costs, net of tax of $163 and $159, respectively	299	282
Net change for employee benefit plan	299	(552)
Change in cumulative foreign currency translation adjustment	30
TOTAL OTHER COMPREHENSIVE INCOME (LOSS)	314	(703)
COMPREHENSIVE INCOME	$ 10,679	$ 1,246