CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Comprehensive income:
Net income	$ 79,416	$ 69,135	$ 74,636
Derivative instruments:
Reclassification of losses to net income, net of tax of $50 and $51, and $51, respectively.	76	76	76
Other comprehensive income	76	76	76
Comprehensive income	$ 79,492	$ 69,211	$ 74,712