Cash, Cash Equivalents and Investments - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Cash balance included foreign bank balance	$ 68,076,000	$ 39,279,000
Gross realized gains on sale of debt securities	292,000	549,000	$ 843,000
Gross realized losses on sale of debt securities	101,000	205,000	$ 170,000
Maximum amount committed to invest in limited partnership	20,500,000
Contribution to limited partnership	19,886,000
Remaining amount of commitment in limited partnership	614,000
Contributions made during the year	0
Proceeds from Limited Partnership Investments	2,257,000
Carrying value of investment	0	$ 942,000
Return of capital	942,000
Cost method investment, investment income	$ 1,315,000