Income Taxes - Summary of reconciliation between federal statutory rate and effective tax rate (Details 1)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes
Federal statutory rate	35.00%	35.00%	35.00%
State income taxes, net of federal benefit	1.90%	1.30%	0.00%
Tax credits	(0.70%)	0.10%	0.30%
Non-deductible expenses	2.00%	(0.70%)	(1.30%)
Change in contingencies	0.00%	6.60%	0.00%
Adjustments related to the Act	(8.30%)
Other	0.30%	(1.30%)	0.90%
Effective tax rate	30.20%	41.00%	34.90%

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to changes in the income tax rates.

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