Investments - Investment Securities Continuous Unrealized Loss Position (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Investment [Line Items]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 87,871	$ 68,985
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than Twelve Months, Accumulated Loss	239	1,188
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	1,746	2,227
Held-to-maturity Securities, Continuous Unrealized Loss Position Twelve Months Or Longer, Accumulated Loss	85	150
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	89,617	71,212
Held-to-maturity Securities, Gross Unrealized Losses	324	1,338
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	87,150	138,107
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	499	6,191
Available-for Sale Fair, Value of Investments with Unrealized Losses, 12 Months or Greater	18,165	7,525
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	3,595	2,844
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	105,315	145,632
Available-for Sale, Gross Unrealized Losses, Total	4,094	9,035
Fair Value of Investments with Unrealized Losses, Less Than 12 months	175,021	207,092
Gross Unrealized Loss, Less Than 12 Months	738	7,379
Fair Value of Investments with Unrealized Losses, 12 Months or Greater	19,911	9,752
Gross Unrealized Losses, 12 Months or Greater	3,680	2,994
Fair Value of Investments with Unrealized Losses, Total	194,932	216,844
Gross Unrealized Losses, Total	4,418	10,373
Corporate Bonds [Member]
Investment [Line Items]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	77,260	14,090
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than Twelve Months, Accumulated Loss	204	41
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	77,260	14,090
Held-to-maturity Securities, Gross Unrealized Losses	204	41
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	78,350	29,691
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	314	361
Available-for Sale Fair, Value of Investments with Unrealized Losses, 12 Months or Greater
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	78,350	29,691
Available-for Sale, Gross Unrealized Losses, Total	314	361
States and Political Subdivisions [Member]
Investment [Line Items]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	7,760	54,895
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than Twelve Months, Accumulated Loss	34	1,147
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		311
Held-to-maturity Securities, Continuous Unrealized Loss Position Twelve Months Or Longer, Accumulated Loss		6
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	7,760	55,206
Held-to-maturity Securities, Gross Unrealized Losses	34	1,153
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	6,894	101,908
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	33	4,798
Available-for Sale Fair, Value of Investments with Unrealized Losses, 12 Months or Greater	11,070	1,753
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	1,566	342
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	17,964	103,661
Available-for Sale, Gross Unrealized Losses, Total	1,599	5,140
U.S. Agency-Based Mortgage-Backed Securities [Member]
Investment [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	724	1,303
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	60	465
Available-for Sale Fair, Value of Investments with Unrealized Losses, 12 Months or Greater	7,095	5,772
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater	2,029	2,502
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	7,819	7,075
Available-for Sale, Gross Unrealized Losses, Total	2,089	2,967
Equity securities [Member]
Investment [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	1,182	5,205
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	92	567
Available-for Sale Fair, Value of Investments with Unrealized Losses, 12 Months or Greater
Available-for Sale, Gross Unrealized Losses, 12 Months or Greater
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	1,182	5,205
Available-for Sale, Gross Unrealized Losses, Total	92	567
Asset-Backed Securities [Member]
Investment [Line Items]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	1,746	1,916
Held-to-maturity Securities, Continuous Unrealized Loss Position Twelve Months Or Longer, Accumulated Loss	85	144
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	1,746	1,916
Held-to-maturity Securities, Gross Unrealized Losses	85	144
U.S. Treasury securities and obligations of U.S. Government agencies [Member]
Investment [Line Items]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	2,851
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than Twelve Months, Accumulated Loss	1
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	2,851
Held-to-maturity Securities, Gross Unrealized Losses	$ 1