Income Taxes (Tables)

6 Months Ended

Jun. 30, 2018

Effective Tax Rate Reconciliation Table [Abstract]

Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]

The sources and tax effects of the differences are reflected in the table below:

	Three months ended June 30,										Six months ended June 30,
$ in thousands	2018			Tax rate %		2017			Tax rate %		2018			Tax rate %		2017			Tax rate %
Expected income tax (provision) benefit based on US statutory tax rate (1)	$	(66,716	)	21	%	$	35,494		35	%	$	(130,867	)	21	%	$	33,222		35	%
State income taxes, net of federal benefit	(9,531		)	3	%	3,043			3	%	(18,695		)	3	%	2,848			3	%
Tax benefit (deficiency) from stock-based compensation	359			—	%	(473		)	(1	%)	1,868			—	%	(3,773		)	(4	%)
Canadian valuation allowance (2)	(78		)	—	%	(112		)	—	%	(148		)	—	%	(257		)	—	%
Other, net	734			—	%	(97		)	—	%	1,074			—	%	(207		)	—	%
(Provision) benefit for income taxes	$	(75,232	)	24	%	$	37,855		37	%	$	(146,768	)	24	%	$	31,833		34	%

(1) In December 2017 the Tax Cuts and Jobs Act was signed into law, which among other things reduced the U.S. federal corporate income tax rate from 35% to 21% effective January 1, 2018.

(2) Represents valuation allowances recognized against all deferred tax assets associated with operating loss carryforwards generated by the Company's Canadian operations during the respective periods for which the Company does not expect to realize a benefit.