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Basis of Presentation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands | 6 Months Ended
--- | ---
Jun. 30, 2018 | Jun. 30, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items] |  |
Percentage of comparable consolidated amounts | 95.00% | 95.00%
ASU 2016-01 [Member] |  |
New Accounting Pronouncements Or Change In Accounting Principle [Line Items] |  |
Decrease in net income | $ 390 |
ASU 2016-01 [Member] | Common Shares [Member] |  |
New Accounting Pronouncements Or Change In Accounting Principle [Line Items] |  |
Decrease in diluted earnings per common share | $ 0.02 |

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