Income Taxes Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Computed expected tax expense	21.00%	21.00%	28.10%	35.00%	35.00%
Deferred Tax Assets, Valuation Allowance	$ 415		$ 515
Income Taxes Paid	62,005		60,382		$ 96,074
Unrecognized Tax Benefits	10,495		10,227		5,449
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	9,892		9,366
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	1,514		1,279
Income Tax penalties and interest expense (or benefits) included in income tax provision	128		$ 165		$ (105)
Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards	4,542
State and Local Jurisdiction [Member]
Operating Loss Carryforwards	651
Minimum [Member]
Expiration of statutes of limitations impact on UTB balance	3,000
Maximum [Member]
Expiration of statutes of limitations impact on UTB balance	$ 4,000