Significant Accounting Policies - Additional Information (Details) - USD ($)		3 Months Ended	9 Months Ended	12 Months Ended
Jan. 01, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Accounting Policies [Abstract]
Cash and cash equivalents held by foreign subsidiaries and branch offices		$ 8,100,000		$ 8,100,000
Cumulative-effect adjustment to opening retained earnings		$ 400,000		$ 400,000
U.S. income tax rate	21.00%	24.50%	35.00%	24.50%	35.00%	35.00%
Valuation allowance against net deferred tax assets		$ 0		$ 0
Unrecorded excess tax benefits in additional paid-in-capital account				0
Restricted cash		$ 0		$ 0

Cash and cash equivalents held by foreign subsidiaries.

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- Definition

Unrecorded excess tax benefits in additional paid-in-capital account.

+ References

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to increase (decrease) in the valuation allowance for deferred tax assets.

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Amount of cumulative effect of the change in accounting principle or new accounting pronouncement on retained earnings or other components of equity or net assets in the statement of financial position as of the beginning of the earliest period presented.

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Amount of cash and cash equivalents restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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