CONSOLIDATED STATEMENTS OF OTHER COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
CONSOLIDATED STATEMENTS OF OTHER COMPREHENSIVE INCOME
Net income (loss)	$ 72,245	$ 53,649	$ 231,194	$ 22,117	$ 28,573	$ 10,645	$ 6,272	$ (5,108)	$ 379,205	$ 40,382	$ (50,750)
Other comprehensive loss before tax:
Actuarial loss on defined benefit pension plan									(1,674)	0	0
Reduction of unrealized gain related to cash flow hedging instruments									0	(1,709)	(1,207)
Unrealized (loss) gain on marketable securities, available-for-sale:
Unrealized (loss) gain									(279)	1,217	360
Less: reclassification adjustments for losses (gains) included in net income (loss)									64	(233)	(1,358)
Total unrealized (loss) gain on marketable securities, available-for-sale									(215)	984	(998)
Other comprehensive loss before tax									(1,889)	(725)	(2,205)
Income tax benefit related to items of other comprehensive loss									640	653	502
Other comprehensive loss, net of tax									(1,249)	(72)	(1,703)
Comprehensive income (loss)									$ 377,956	$ 40,310	$ (52,453)