New Accounting Pronouncements - Additional Information (Details) - USD ($)	9 Months Ended	12 Months Ended
Sep. 30, 2018	Dec. 31, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Income tax effects from Tax Act	$ 19,997,000	$ 20,153,000
ASU 2018-02
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Adjustment against retained earnings for effect of change in federal corporate income tax rate	40,000
Adjustments related to valuation allowance	0
Income tax effects from Tax Act	$ 0
ASU 2016-02
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Maximum percentage of right-of-use assets and liabilities expected to be recognized upon adoption of ASU	5.00%
ASU 2016-16
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Favorable adjustment to retained earnings	$ 31,645,000

Maximum percentage right of use assets to be recognized upon adoption of ASU.

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- Definition

Tax cuts and jobs act of 2017, incomplete accounting, provisional income tax expense (benefit).

+ References

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- Definition

Amount of increase (decrease) in accumulated other comprehensive income (AOCI) for reclassification to retained earnings of tax effect from remeasurement of deferred tax pursuant to Tax Cuts and Jobs Act.

+ References

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- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Amount of increase (decrease) in valuation and qualifying accounts and reserves from adjustment.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
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