Components of net periodic benefit cost (Details 3) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 155	$ 1,078	$ 2,252
Interest cost	16,249	17,598	19,500
Expected return on assets	(19,917)	(23,536)	(22,809)
Amortization of prior service cost (credit)	71	(46)	45
Recognized net actuarial loss	7,173	7,070	4,656
Curtailment loss (gain)	0	(1,023)	1,218
Amortization of net transition obligation	0	0	0
Net periodic benefit cost, including amount capitalized	3,731	1,141	4,862
Less amount capitalized	727	937	1,196
Net periodic benefit cost	3,004	204	3,666
Other changes in plan assets and benefit obligations recognized in accumulated other comprehensive (income) loss:
Net (gain) loss	(60,173)	19,982	76,310
Prior service cost (credit)	0	0	0
Amortization of actuarial loss	(7,173)	(7,070)	(4,656)
Amortization of prior service (cost) credit	(71)	1,069	(1,263)
Amortization of net transition obligation	0	0	0
Total recognized in accumulated other comprehensive (income) loss	(67,417)	13,981	70,391
Total recognized in net periodic benefit cost and accumulated other comprehensive (income) loss	(64,413)	14,185	74,057
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	1,675	1,747	1,443
Interest cost	3,215	4,166	4,700
Expected return on assets	(4,343)	(4,890)	(5,051)
Amortization of prior service cost (credit)	(1,457)	(1,438)	(2,677)
Recognized net actuarial loss	1,814	2,134	753
Curtailment loss (gain)	0	0	0
Amortization of net transition obligation	0	2,128	2,125
Net periodic benefit cost, including amount capitalized	904	3,847	1,293
Less amount capitalized	164	910	(50)
Net periodic benefit cost	740	2,937	1,343
Other changes in plan assets and benefit obligations recognized in accumulated other comprehensive (income) loss:
Net (gain) loss	(30,461)	1,863	23,863
Prior service cost (credit)	0	(11,418)	0
Amortization of actuarial loss	(1,814)	(2,134)	(753)
Amortization of prior service (cost) credit	1,457	1,438	2,677
Amortization of net transition obligation	0	(2,128)	(2,125)
Total recognized in accumulated other comprehensive (income) loss	(30,818)	(12,379)	23,662
Total recognized in net periodic benefit cost and accumulated other comprehensive (income) loss	$ (30,078)	$ (9,442)	$ 25,005

The total amount of net periodic benefit cost for defined benefit plans capitalized for the period. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain or loss, prior service cost or credit, transition asset or obligation, and gain or loss due to settlements or curtailments).

No definition available.