Securities with Gross Unrealized Losses in Continuous Loss Position (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Marketable Securities, Less Than 12 Months Gross Unrealized Losses	$ 16,836
Marketable Securities, Less Than 12 Months Fair Value	401,706
Marketable Securities, Over 12 Months Gross Unrealized Losses	132
Marketable Securities, Over 12 Months Fair Value	1,650
Available for sale, Less Than 12 Months Gross Unrealized Losses	8,835	740
Available for sale, Less Than 12 Months Fair Value	238,361	72,507
Available for sale, Over 12 Months Gross Unrealized Losses	132	69
Available for sale, Over 12 Months Fair Value	1,650	1,684
Held to maturity, Less Than 12 Months Gross Unrealized Losses	8,001
Held to maturity, Less Than 12 Months Fair Value	163,345
Held to maturity, Over 12 Months Gross Unrealized Losses
Held to maturity, Over 12 Months Fair Value
Government sponsored residential mortgage-backed securities
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Available for sale, Less Than 12 Months Gross Unrealized Losses	6,904	631
Available for sale, Less Than 12 Months Fair Value	176,006	49,081
Available for sale, Over 12 Months Gross Unrealized Losses
Available for sale, Over 12 Months Fair Value
Held to maturity, Less Than 12 Months Gross Unrealized Losses	4,101
Held to maturity, Less Than 12 Months Fair Value	83,536
Held to maturity, Over 12 Months Gross Unrealized Losses
Held to maturity, Over 12 Months Fair Value
U.S. government guaranteed mortgage-backed securities
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Available for sale, Less Than 12 Months Gross Unrealized Losses	598
Available for sale, Less Than 12 Months Fair Value	26,037
Available for sale, Over 12 Months Gross Unrealized Losses
Available for sale, Over 12 Months Fair Value
Held to maturity, Less Than 12 Months Gross Unrealized Losses	879
Held to maturity, Less Than 12 Months Fair Value	20,964
Held to maturity, Over 12 Months Gross Unrealized Losses
Held to maturity, Over 12 Months Fair Value
Corporate bonds
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Available for sale, Less Than 12 Months Gross Unrealized Losses	449	63
Available for sale, Less Than 12 Months Fair Value	15,064	4,330
Available for sale, Over 12 Months Gross Unrealized Losses
Available for sale, Over 12 Months Fair Value
Held to maturity, Less Than 12 Months Gross Unrealized Losses	844
Held to maturity, Less Than 12 Months Fair Value	22,195
Held to maturity, Over 12 Months Gross Unrealized Losses
Held to maturity, Over 12 Months Fair Value
State and municipal bonds
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Available for sale, Less Than 12 Months Gross Unrealized Losses	10	9
Available for sale, Less Than 12 Months Fair Value	379	1,178
Available for sale, Over 12 Months Gross Unrealized Losses
Available for sale, Over 12 Months Fair Value
Held to maturity, Less Than 12 Months Gross Unrealized Losses	302
Held to maturity, Less Than 12 Months Fair Value	4,434
Held to maturity, Over 12 Months Gross Unrealized Losses
Held to maturity, Over 12 Months Fair Value
Government sponsored enterprise obligations
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Available for sale, Less Than 12 Months Gross Unrealized Losses	845	37
Available for sale, Less Than 12 Months Fair Value	16,614	17,918
Available for sale, Over 12 Months Gross Unrealized Losses
Available for sale, Over 12 Months Fair Value
Held to maturity, Less Than 12 Months Gross Unrealized Losses	1,875
Held to maturity, Less Than 12 Months Fair Value	32,216
Held to maturity, Over 12 Months Gross Unrealized Losses
Held to maturity, Over 12 Months Fair Value
Mutual funds
Schedule Of Available For Sale Securities And Held To Maturity Securities [Line Items]
Available for sale, Less Than 12 Months Gross Unrealized Losses	29
Available for sale, Less Than 12 Months Fair Value	4,261
Available for sale, Over 12 Months Gross Unrealized Losses	132	69
Available for sale, Over 12 Months Fair Value	$ 1,650	$ 1,684