Income Taxes - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Additional income tax expense due to remeasurement of deferred tax balances	$ 8,800,000
Effective income tax rate (percent)	9.30%	29.40%	32.60%
Deferred tax assets, valuation allowance	$ 0	$ 0
Accrued interest and penalties related to unrecognized tax benefits	100,000	100,000
Unrecognized tax benefits that would impact the effective tax rate	2,000,000	700,000
U.S.
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	6,000,000
State
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	1,900,000
Existing Net Operating Loss
Operating Loss Carryforwards [Line Items]
Additions to unrecognized tax benefit	300,000
Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Additions to unrecognized tax benefit	1,000,000	$ 200,000	$ 300,000
Research Tax Credit Carryforward | U.S.
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	2,200,000
Research Tax Credit Carryforward | State
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	$ 1,400,000