Fair Value Measurements - Fair Values and Unrealized Losses on Securities Available-for-Sale (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Schedule Of Available For Sale Securities [Line Items]
Less than Twelve Months, Estimated fair value	$ 15,357	$ 22,626
Less than Twelve Months, Gross unrealized losses	(8)	(31)
Estimated fair value, Total	15,357	22,626
Gross unrealized losses, Total	(8)	(31)
Municipal Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than Twelve Months, Estimated fair value	3,170	2,139
Less than Twelve Months, Gross unrealized losses		(2)
Estimated fair value, Total	3,170	2,139
Gross unrealized losses, Total		(2)
Corporate Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than Twelve Months, Estimated fair value	12,187	20,487
Less than Twelve Months, Gross unrealized losses	(8)	(29)
Estimated fair value, Total	12,187	20,487
Gross unrealized losses, Total	$ (8)	$ (29)