CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
Net income	$ 406,282	$ 4,966	$ 5,990
Available-for-sale investment items:
Net unrealized losses on available-for-sale investments	(1,455)	(2,032)	0
Reclassification of other-than-temporary impairment losses included in earnings	1,295	0	0
Reclassification of realized losses (gains) included in earnings	833	(93)	0
Total before income taxes	673	(2,125)	0
Income tax benefit	127	0	0
Total	800	(2,125)	0
Defined benefit pension items:
Net (loss) gain arising during the period	(2,180)	2,191	(2,485)
Amortization and settlement included in net periodic cost	7,107	743	1,162
Amortization of loss included in net periodic cost	465	326	48
Amortization and curtailment of prior service cost included in net periodic cost	0	0	2,503
Total before income taxes	5,392	3,260	1,228
Income tax expense	0	0	0
Total	5,392	3,260	1,228
Total other comprehensive income, net of tax	6,192	1,135	1,228
Total comprehensive income	$ 412,474	$ 6,101	$ 7,218