Additional Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash paid during the year for:
Interest	$ 12,435	$ 11,456	$ 11,033
Income taxes	123,651	130,226	129,540
Non-cash financing activities:
Assets acquired under capital lease obligations	$ 1,063	$ 1,252	$ 1,914