Income Taxes - Unrecognized Tax Benefit (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Valuation Allowance [Abstract]
Deferred tax asset valuation allowance	$ 0	$ 0
Reconciliation of unrecognized tax benefits
Balance at the beginning of the year	0	0	$ 0
Additions for current year tax positions	7,719,000	0	0
Reductions for current year tax positions	(4,631,000)	0	0
Additions for prior year tax positions	0	2,337,000	0
Reductions for prior year tax positions	0	(2,337,000)	0
Balance at the end of the year	3,088,000	0	0
Tax expense related to uncertain tax positions	$ 3,088,000	0	0
Effective income tax rate change as a result of tax law change (percent)	0.80%
Current liability for uncertain tax position		2,300,000
Interest expense related to uncertain tax positions	$ 800,000	$ 100,000	$ 0