Investments - Summary of Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	$ 27,361	$ 15,664
Unrealized Losses, Less than 12 Months	(98)	(60)
Fair Value, 12 Months or More	0	0
Unrealized Losses, 12 Months or More	0	0
Fair Value	27,361	15,664
Unrealized Losses	(98)	(60)
U.S. Treasury securities, obligations of U.S. Government agencies and Municipals
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	26,886	14,663
Unrealized Losses, Less than 12 Months	(98)	(59)
Fair Value, 12 Months or More	0	0
Unrealized Losses, 12 Months or More	0	0
Fair Value	26,886	14,663
Unrealized Losses	(98)	(59)
Corporate debt
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	475	1,001
Unrealized Losses, Less than 12 Months	0	(1)
Fair Value, 12 Months or More	0	0
Unrealized Losses, 12 Months or More	0	0
Fair Value	475	1,001
Unrealized Losses	$ 0	$ (1)