Income Taxes (Schedule of Components of Earnings before Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
United States									$ 196,827	$ 113,280	$ 95,057
Foreign									2,345	1,089	0
Income before income taxes	$ 40,203	$ 44,742	$ 58,975	$ 55,252	$ 23,125	$ 26,576	$ 33,019	$ 31,649	$ 199,172	$ 114,369	$ 95,057