Effective Tax Rate Reconciliation (Details)	12 Months Ended
	Jun. 30, 2019 Rate	Dec. 31, 2018 Rate	Jun. 30, 2018 Rate	Dec. 31, 2017 Rate	Jun. 30, 2017 Rate
Income Tax Disclosure [Abstract]
Computed expected tax expense	21.00%	21.00%	28.10%	35.00%	35.00%
State income taxes, net of federal income tax benefits	3.70%		2.90%		2.60%
Research and development credit	(2.50%)		(2.00%)		(2.10%)
Domestic production activities deduction	(0.00%)		(1.40%)		(2.30%)
TCJA deferred tax rate re-measurement	(0.00%)		(30.00%)		(0.00%)
Tax effects of share-based payments	(1.40%)		(0.80%)		(0.80%)
Other (net)	0.90%		0.70%		0.30%
Effective Income Tax Rate	21.70%		(2.50%)		32.70%