Investments - Summary of Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	$ 28,638	$ 18,094
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	24	40
Fair Value, Less than 12 Months	15,664	11,779
Unrealized Losses, Less than 12 Months	(60)	(40)
Fair Value, 12 Months or More	0	284
Unrealized Losses, 12 Months or More	0	(2)
Fair Value	15,664	12,063
Unrealized Losses	(60)	(42)
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(60)	(42)
Available-for-sale Securities	28,602	18,092
U.S. Treasury securities, obligations of U.S. Government agencies and Municipals
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	26,280	11,876
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	11	6
Fair Value, Less than 12 Months	14,663	8,998
Unrealized Losses, Less than 12 Months	(59)	(26)
Fair Value, 12 Months or More	0	0
Unrealized Losses, 12 Months or More	0	0
Fair Value	14,663	8,998
Unrealized Losses	(59)	(26)
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(59)	(26)
Available-for-sale Securities	26,232	11,856
Foreign government
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		50
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax		0
Fair Value, Less than 12 Months	0	50
Unrealized Losses, Less than 12 Months	0	0
Fair Value, 12 Months or More	0	0
Unrealized Losses, 12 Months or More	0	0
Fair Value	0	50
Unrealized Losses	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		0
Available-for-sale Securities		50
Corporate debt
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	2,358	4,505
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	13	7
Fair Value, Less than 12 Months	1,001	2,731
Unrealized Losses, Less than 12 Months	(1)	(14)
Fair Value, 12 Months or More	0	284
Unrealized Losses, 12 Months or More	0	(2)
Fair Value	1,001	3,015
Unrealized Losses	(1)	(16)
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(1)	(16)
Available-for-sale Securities	$ 2,370	4,496
Short Duration Fixed Income Fund [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		1,663
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax		27
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		0
Available-for-sale Securities		$ 1,690