Consolidated Statement of Comprehensive Income - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015		Sep. 30, 2014
Net income		$ 21,798	$ 33,154	$ 28,165		$ 69,774
Other comprehensive income, net of tax:
Amortization of prior service credit included in net periodic cost, net of tax of $(850), $(867), $(2,547) and $(2,601)	[1]	(1,327)	(1,357)	(3,983)		(4,069)
Amortization of actuarial loss included in net periodic cost, net of tax of $2,009, $1,621, $5,846 and $4,866	[1]	3,139	2,538	9,142		7,612
Other comprehensive income, net of tax	[1]	1,812	1,181	5,159		3,543
Comprehensive income		$ 23,610	$ 34,335	$ 33,324	[1]	$ 73,317

[1] Amortization of prior service credit (cost) and amortization of actuarial loss are included in the computation of net periodic cost (benefit).