Income Taxes - Narrative (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Income Taxes [Line Items]
Effective income tax rate	18.30%	(37.70%)
Valuation allowance	$ 0
Testing period	5 years
AMT credit carryovers	$ 1,400,000
Provisional income tax expense			$ 23,100,000
Unrecognized tax benefits	0
Federal
Income Taxes [Line Items]
Operating loss carryforwards	0
Unused built-in losses	48,500,000
State
Income Taxes [Line Items]
Operating loss carryforwards	49,900,000
Unused built-in losses	$ 7,500,000