Long-Term Debt (Narrative) (Details)			12 Months Ended
	Aug. 24, 2018 USD ($)	Mar. 21, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Credit facility amount outstanding			$ 0	$ 0
Prosperity Bank [Member]
Debt Instrument [Line Items]
Credit facility maturity date			Jul. 31, 2020
Rate above prime	0.50%	0.50%
Interest rate	5.50%	5.00%	6.00%
Credit facility maximum borrowing capacity	$ 2,740,000	$ 2,000,000	$ 50,000,000
Credit facility current borrowing capacity	$ 3,000,000		2,740,000
Credit facility amount outstanding			0
Credit limit			2,740,000
Prosperity Bank [Member] | Loans And Letters Of Credit [Member]
Debt Instrument [Line Items]
Credit facility maximum borrowing capacity			$ 50,000,000
Maximum [Member] | Prosperity Bank [Member]
Debt Instrument [Line Items]
Funded debt to EBITDA			3.5
Minimum [Member] | Prosperity Bank [Member]
Debt Instrument [Line Items]
Current ratio			1
Interest coverage			3.0