Income Taxes - Income tax expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Current	$ 38,082	$ 17,185	$ 5,451
Deferred	14,909	32,630	60,951
Increase in valuation allowance	0	0	413
Expense due to enactment of federal tax reform	0	0	38,198
Total income tax expense	$ 52,991	$ 49,815	$ 105,013