Investments - Investment Securities Continuous Unrealized Loss Position (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Investment [Line Items]
Fair Value of Investments with Unrealized Losses, Less Than 12 months	$ 207,092	$ 50,561
Gross Unrealized Loss, Less Than 12 Months	7,379	1,828
Fair Value of Investments with Unrealized Losses, 12 Months or Greater	9,752	2,345
Gross Unrealized Losses	1,338	299
Gross Unrealized Losses, 12 Months or Greater	2,994	181
Fair Value of Investments with Unrealized Losses, Total	216,844	52,906
Gross Unrealized Losses, Total	10,373	2,009
Available-for-sale securities [Member]
Investment [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	138,107	27,797
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	6,191	1,710
Fair Value of Investments with Unrealized Losses, 12 Months or Greater	7,525
Gross Unrealized Losses, 12 Months or Greater	2,844
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	145,632	27,797
Available-for Sale, Gross Unrealized Losses, Total	9,035	1,710
Available-for-sale securities [Member] | Corporate bonds [Member]
Investment [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	29,691	6,411
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	361	24
Fair Value of Investments with Unrealized Losses, 12 Months or Greater
Gross Unrealized Losses, 12 Months or Greater
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	29,691	6,411
Available-for Sale, Gross Unrealized Losses, Total	361	24
Available-for-sale securities [Member] | States and political subdivisions [Member]
Investment [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	101,908	6,281
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	4,798	142
Fair Value of Investments with Unrealized Losses, 12 Months or Greater	1,753
Gross Unrealized Losses, 12 Months or Greater	342
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	103,661	6,281
Available-for Sale, Gross Unrealized Losses, Total	5,140	142
Available-for-sale securities [Member] | 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	1,303	10,919
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	465	859
Fair Value of Investments with Unrealized Losses, 12 Months or Greater	5,772
Gross Unrealized Losses, 12 Months or Greater	2,502
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	7,075	10,919
Available-for Sale, Gross Unrealized Losses, Total	2,967	859
Available-for-sale securities [Member] | Equity securities [Member]
Investment [Line Items]
Available-for Sale, Fair value of Investments with Unrealized Losses, Less Than 12 Months	5,205	4,186
Available-for Sale, Gross Unrealized Losses, Less Than 12 Months	567	685
Fair Value of Investments with Unrealized Losses, 12 Months or Greater
Gross Unrealized Losses, 12 Months or Greater
Available-for Sale, Fair Value of Investments with Unrealized Losses, Total	5,205	4,186
Available-for Sale, Gross Unrealized Losses, Total	567	685
Held-to-maturity securities [Member]
Investment [Line Items]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	68,985	22,764
Held To Maturity Securities Continuous Unrealized Loss Position Less Than Twelve Months Accumulated Loss	1,188	118
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	2,227	2,345
Held To Maturity Securities, Continuous Unrealized Loss Position Twelve Months Or Longer Accumulated Loss	150	181
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	71,212	25,109
Gross Unrealized Losses	1,338	299
Held-to-maturity securities [Member] | Corporate bonds [Member]
Investment [Line Items]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	14,090	10,734
Held To Maturity Securities Continuous Unrealized Loss Position Less Than Twelve Months Accumulated Loss	41	12
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value
Held To Maturity Securities, Continuous Unrealized Loss Position Twelve Months Or Longer Accumulated Loss
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	14,090	10,734
Gross Unrealized Losses	41	12
Held-to-maturity securities [Member] | States and political subdivisions [Member]
Investment [Line Items]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	54,895	11,913
Held To Maturity Securities Continuous Unrealized Loss Position Less Than Twelve Months Accumulated Loss	1,147	106
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	55,206	11,913
Gross Unrealized Losses	1,153	106
Held-to-maturity securities [Member] | U.S. agency-based mortgage-backed securities [Member]
Investment [Line Items]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		117
Held To Maturity Securities Continuous Unrealized Loss Position Less Than Twelve Months Accumulated Loss
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		68
Held To Maturity Securities, Continuous Unrealized Loss Position Twelve Months Or Longer Accumulated Loss		5
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value		185
Gross Unrealized Losses		5
Held-to-maturity securities [Member] | Asset-backed securities [Member]
Investment [Line Items]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value
Held To Maturity Securities Continuous Unrealized Loss Position Less Than Twelve Months Accumulated Loss
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	1,916	2,277
Held To Maturity Securities, Continuous Unrealized Loss Position Twelve Months Or Longer Accumulated Loss	144	176
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	1,916	2,277
Gross Unrealized Losses	$ 144	$ 176