Consolidated Statement of Comprehensive Income Loss) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)		$ (31,238)	$ 711	$ (31,081)	$ 6,367
Other comprehensive income, net of tax:
Amortization of prior service credit included in net periodic cost, net of tax of $(815), $(848), $(1,630) and $(1,697)	[1]	(1,274)	(1,328)	(2,549)	(2,656)
Amortization of actuarial loss included in net periodic cost, net of tax of $1,826, $1,900, $3,521 and $3,837	[1]	2,857	2,974	5,507	6,003
Cash flow hedge, net of tax of $(264), $-, $(369) and $-		(413)	0	(577)	0
Other comprehensive income, net of tax		1,170	1,646	2,381	3,347
Comprehensive income (loss)		$ (30,068)	$ 2,357	$ (28,700)	$ 9,714

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