Subsequent Event (Details) - Revolving Credit Facility - USD ($)	Feb. 19, 2019	Apr. 12, 2018	Feb. 22, 2017	Feb. 21, 2019
Subsequent Event [Line Items]
Maximum borrowing capacity			$ 100,000,000
Federal Funds Effective Swap Rate
Subsequent Event [Line Items]
Basis spread			0.50%
Eurodollar
Subsequent Event [Line Items]
Basis spread		1.00%
Applicable margin		0.0175
Base Rate
Subsequent Event [Line Items]
Applicable margin		0.0075
Letter of Credit Sublimit
Subsequent Event [Line Items]
Maximum borrowing capacity		$ 65,000,000
Revolver Swing Line Supplement
Subsequent Event [Line Items]
Maximum borrowing capacity		$ 10,000,000
Subsequent Event
Subsequent Event [Line Items]
Maximum borrowing capacity				$ 165,000,000
Optional borrowing capacity				200,000,000
Right to increase the Revolver	$ 50,000,000
Borrower Obligations, capital stock of first-tier foreign subsidiaries, percent	65.00%
Subsequent Event | Federal Funds Effective Swap Rate
Subsequent Event [Line Items]
Basis spread	0.50%
Subsequent Event | Eurodollar
Subsequent Event [Line Items]
Basis spread	1.00%
Applicable margin	0.0175
Subsequent Event | Base Rate
Subsequent Event [Line Items]
Applicable margin	0.0075
Subsequent Event | Letter of Credit Sublimit
Subsequent Event [Line Items]
Maximum borrowing capacity				100,000,000
Subsequent Event | Revolver Swing Line Supplement
Subsequent Event [Line Items]
Maximum borrowing capacity				$ 15,000,000