Investments - Gross Unrealized Losses by Current Severity and Length of Time that Individual Securities have been in Continuous Unrealized Loss Position (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Investment Maturity Date [Line Items]
Fair Value of Securities with Gross Unrealized Losses	$ 37,921	$ 27,035
Gross Unrealized Losses	(2,291)	(350)
Less Than 5% [Member]
Investment Maturity Date [Line Items]
Gross Unrealized Losses	(278)	(252)
5% to 10% [Member]
Investment Maturity Date [Line Items]
Gross Unrealized Losses	(2,013)
Greater Than 10% [Member]
Investment Maturity Date [Line Items]
Gross Unrealized Losses		(98)
Three Months [Member]
Investment Maturity Date [Line Items]
Fair Value of Securities with Gross Unrealized Losses	6,417	26,121
Gross Unrealized Losses	(40)	(266)
Three Months [Member] | Less Than 5% [Member]
Investment Maturity Date [Line Items]
Gross Unrealized Losses	(40)	(246)
Three Months [Member] | 5% to 10% [Member]
Investment Maturity Date [Line Items]
Gross Unrealized Losses
Three Months [Member] | Greater Than 10% [Member]
Investment Maturity Date [Line Items]
Gross Unrealized Losses		(20)
Six Months [Member]
Investment Maturity Date [Line Items]
Fair Value of Securities with Gross Unrealized Losses	1,653
Gross Unrealized Losses	(129)
Six Months [Member] | Less Than 5% [Member]
Investment Maturity Date [Line Items]
Gross Unrealized Losses
Six Months [Member] | 5% to 10% [Member]
Investment Maturity Date [Line Items]
Gross Unrealized Losses	(129)
Six Months [Member] | Greater Than 10% [Member]
Investment Maturity Date [Line Items]
Gross Unrealized Losses
Nine Months [Member]
Investment Maturity Date [Line Items]
Fair Value of Securities with Gross Unrealized Losses	15,871
Gross Unrealized Losses	(852)
Nine Months [Member] | Less Than 5% [Member]
Investment Maturity Date [Line Items]
Gross Unrealized Losses	(153)
Nine Months [Member] | 5% to 10% [Member]
Investment Maturity Date [Line Items]
Gross Unrealized Losses	(699)
Nine Months [Member] | Greater Than 10% [Member]
Investment Maturity Date [Line Items]
Gross Unrealized Losses
Twelve Months[Member]
Investment Maturity Date [Line Items]
Fair Value of Securities with Gross Unrealized Losses		702
Gross Unrealized Losses		(6)
Twelve Months[Member] | Less Than 5% [Member]
Investment Maturity Date [Line Items]
Gross Unrealized Losses		(6)
Twelve Months[Member] | 5% to 10% [Member]
Investment Maturity Date [Line Items]
Gross Unrealized Losses
Twelve Months[Member] | Greater Than 10% [Member]
Investment Maturity Date [Line Items]
Gross Unrealized Losses
Greater Than 12 Months [Member]
Investment Maturity Date [Line Items]
Fair Value of Securities with Gross Unrealized Losses	13,980	212
Gross Unrealized Losses	(1,270)	(78)
Greater Than 12 Months [Member] | Less Than 5% [Member]
Investment Maturity Date [Line Items]
Gross Unrealized Losses	(85)
Greater Than 12 Months [Member] | 5% to 10% [Member]
Investment Maturity Date [Line Items]
Gross Unrealized Losses	(1,185)
Greater Than 12 Months [Member] | Greater Than 10% [Member]
Investment Maturity Date [Line Items]
Gross Unrealized Losses		$ (78)