Investments - Summary of Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	$ 23,877	$ 15,664
Unrealized Losses, Less than 12 Months	(64)	(60)
Fair Value, 12 Months or More	0	0
Unrealized Losses, 12 Months or More	0	0
Fair Value	23,877	15,664
Unrealized Losses	(64)	(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	23,601	14,663
Unrealized Losses, Less than 12 Months	(64)	(59)
Fair Value, 12 Months or More	0	0
Unrealized Losses, 12 Months or More	0	0
Fair Value	23,601	14,663
Unrealized Losses	(64)	(59)
Foreign government
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months		0
Unrealized Losses, Less than 12 Months		0
Fair Value, 12 Months or More		0
Unrealized Losses, 12 Months or More		0
Fair Value		0
Unrealized Losses		0
Corporate debt
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	276	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	276	1,001
Unrealized Losses	$ 0	$ (1)