Held to Maturity Securities in Continuous Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities, Less than 12 Months, Fair Value		$ 50,574
Held-to-maturity Securities, Less than 12 Months, Unrealized Losses	$ 0	(129)
Held-to-maturity Securities, 12 Months or Longer, Fair Value		0
Held-to-maturity Securities, 12 Months or Longer, Unrealized Losses	$ 0	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value		50,574
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss		(129)
U.S. Agency securities
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities, Less than 12 Months, Fair Value		43,723
Held-to-maturity Securities, Less than 12 Months, Unrealized Losses		(106)
Held-to-maturity Securities, 12 Months or Longer, Fair Value		0
Held-to-maturity Securities, 12 Months or Longer, Unrealized Losses		0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value		43,723
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss		(106)
Corporate securities
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity Securities, Less than 12 Months, Fair Value		6,851
Held-to-maturity Securities, Less than 12 Months, Unrealized Losses		(23)
Held-to-maturity Securities, 12 Months or Longer, Fair Value		0
Held-to-maturity Securities, 12 Months or Longer, Unrealized Losses		0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value		6,851
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss		$ (23)