Investment Securities - Summary of Transfers between Level 1 and Level 2 (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Transfers from Level 2 to Level 1	$ 1,000	$ 11,032
Corporate Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Transfers from Level 2 to Level 1	$ 1,000	5,737
Foreign Corporate Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Transfers from Level 2 to Level 1		$ 5,295