Debt (Details) - USD ($)	Apr. 15, 2018	Mar. 16, 2018	Feb. 15, 2018	Mar. 31, 2018	Dec. 31, 2017
Line of Credit Facility [Line Items]
Amount outstanding				$ 245,402,000	$ 248,320,000
Credit Facility
Line of Credit Facility [Line Items]
Period after effective date		31 days
Debt Instrument, Delayed Draw Fee, Percent		1.25%
Credit Facility | LIBOR
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread On Variable Rate, Reduction In Rate			0.25%
Basis spread on variable interest rate			2.50%
Potential reduction to basis spread on variable rate, pro forma leverage ratio used for calculation			1.00
Credit Facility | Alternate base rate
Line of Credit Facility [Line Items]
Basis spread on variable interest rate			1.50%
Credit Facility | Term loan
Line of Credit Facility [Line Items]
Amount outstanding				258,700,000
Credit Facility | Revolving credit facility
Line of Credit Facility [Line Items]
Borrowing capacity				100,000,000
Amount outstanding				$ 0
Additional Term Loan 2018 | Term loan
Line of Credit Facility [Line Items]
Borrowing capacity			$ 105,000,000
Covenant terms, leverage ratio			2.50
Covenant terms, percent of aggregate revolving commitments			30.00%
Sustainable Growth Advisers, LP
Line of Credit Facility [Line Items]
Percentage of voting interests acquired			70.00%
SGIA, LLC
Line of Credit Facility [Line Items]
Percentage of voting interests acquired			100.00%
Subsequent Event | Credit Facility
Line of Credit Facility [Line Items]
Period after effective date	60 days
Debt Instrument, Delayed Draw Fee, Percent	2.50%