Income Taxes - Summary of reconciliation between federal statutory rate and effective tax rate (Details 1)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes
Federal statutory rate	35.00%	35.00%	35.00%
State income taxes, net of federal benefit	1.30%		3.30%
Tax credits	0.10%	0.30%	(0.70%)
Non-deductible expenses	(0.70%)	(1.30%)	0.40%
Change in contingencies	6.60%
Other	(1.30%)	0.90%	0.60%
Effective tax rate	41.00%	34.90%	38.60%