Income Taxes - Components of Income Tax Expense (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Current Income Tax Expense (Benefit)									$ 25,317	$ 43,148	$ 37,954
Deferred income taxes									2,625	3,221	4,103
Income tax expense	$ 6,193	$ 7,979	$ 7,332	$ 6,438	$ 13,266	$ 11,193	$ 11,124	$ 10,786	$ 27,942	$ 46,369	$ 42,057