Income Taxes (Summary of Tax Expense and Effective Tax Rates) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Income before income taxes	$ 14,584	$ 2,584	$ 79,173	$ 48,118
Income tax expense	$ 4,092	$ 955	$ 17,850	$ 13,519
Effective tax rate (percent)	28.10%	37.00%	22.50%	28.10%