Income taxes Income taxes -(Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Income Tax Disclosure [Abstract]
Income tax benefit (expense) computed by applying the statutory rate	$ 10,246	$ (18,816)	$ 10,283	$ (19,580)
State income tax, net of federal tax benefit and increase in valuation allowance	347	(551)	1,634	(572)
Non-deductible stock-based compensation	(123)	(164)	(239)	(339)
Stock-based compensation tax deficiency	(15)	(120)	(156)	(411)
Change in deferred tax valuation allowance	(34)	(20)	(1,112)	(29)
Other items	(47)	(376)	(143)	(226)
Total income tax benefit (expense)	$ 10,374	$ (20,047)	$ 10,267	$ (21,157)