Recent Accounting Pronouncements - Additional Information (Detail) - USD ($) $ in Thousands		6 Months Ended		12 Months Ended
		Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2016
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Corporate income tax rate		21.00%	34.00%	28.06%	34.00%	34.00%
Retained Earnings [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Reclassification of certain tax effects on other comprehensive income	[1]			$ 1,117
Accumulated Other Comprehensive Income [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Reclassification of certain tax effects on other comprehensive income	[1]			$ (1,117)

[1] The adoption of ASU 2018-02 requires the reclassification from accumulated other comprehensive income to retained earnings of certain stranded income tax effects in accumulated other comprehensive income resulting from the Tax Cuts and Jobs Act of 2017. Refer to Footnote 2 - Recent Accounting Pronouncements for additional information