Postretirement Medical Plan (Tables)

6 Months Ended

Jun. 30, 2015

Postretirement Medical Plan

Schedule of components of net periodic postretirement benefit cost

		Three Months Ended				Six Months Ended
		June 30,				June 30,
		2015		2014		2015		2014
Service cost		$	1,229	$	1,038	$	2,458	$	2,075
Interest cost			482		464		964		929
Amortization of prior service cost			313		247		626		494
	Net periodic benefit cost	$	2,024	$	1,749	$	4,048	$	3,498