STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Comprehensive income:
Net income	$ 127,263	$ 129,852	$ 95,177
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, Net of Tax	(464)	0	0
Derivative instruments:
Reclassification of losses to net income, net of tax of $97, $96, and $97, respectively	172	172	171
Other comprehensive income	(292)	172	171
Comprehensive income	$ 126,971	$ 130,024	$ 95,348