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	Jun. 30, 2014	Dec. 31, 2013
Investment Maturity Date [Line Items]
Fair Value of Securities with Gross Unrealized Losses	$ 30,690	$ 37,921
Gross Unrealized Losses	(1,050)	(2,291)
Less Than 5% [Member]
Investment Maturity Date [Line Items]
Gross Unrealized Losses	(575)	(278)
5% to 10% [Member]
Investment Maturity Date [Line Items]
Gross Unrealized Losses	(475)	(2,013)
Greater Than 10% [Member]
Investment Maturity Date [Line Items]
Gross Unrealized Losses
Three Months [Member]
Investment Maturity Date [Line Items]
Fair Value of Securities with Gross Unrealized Losses	4,172	6,417
Gross Unrealized Losses	(2)	(40)
Three Months [Member] | Less Than 5% [Member]
Investment Maturity Date [Line Items]
Gross Unrealized Losses	(2)	(40)
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
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	999	15,871
Gross Unrealized Losses	(5)	(852)
Nine Months [Member] | Less Than 5% [Member]
Investment Maturity Date [Line Items]
Gross Unrealized Losses	(5)	(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	1,628
Gross Unrealized Losses	(127)
Twelve Months [Member] | Less Than 5% [Member]
Investment Maturity Date [Line Items]
Gross Unrealized Losses
Twelve Months [Member] | 5% to 10% [Member]
Investment Maturity Date [Line Items]
Gross Unrealized Losses	(127)
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	23,891	13,980
Gross Unrealized Losses	(916)	(1,270)
Greater Than 12 Months [Member] | Less Than 5% [Member]
Investment Maturity Date [Line Items]
Gross Unrealized Losses	(568)	(85)
Greater Than 12 Months [Member] | 5% to 10% [Member]
Investment Maturity Date [Line Items]
Gross Unrealized Losses	(348)	(1,185)
Greater Than 12 Months [Member] | Greater Than 10% [Member]
Investment Maturity Date [Line Items]
Gross Unrealized Losses