RetirementBenefit Plans - Fair Values Measurements of Pension Plan Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	$ 491,550	$ 438,708
Cash and Equivalents [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	44,224	10,243
Total Cash and Cash-Equivalents [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	44,224	10,243
U.S. Government and Agency Securities [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	11,192	15,518
Municipal Securities [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	31,190	33,980
Emerging Market Debt Fund [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	24,482	19,505
Foreign Bonds Notes And Debentures [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	1,743	2,588
Hancock Horizon Core Bond Fund [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	47,453	51,529
Corporate Debt Securities [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	61,481	62,429
Other Fixed Income Securities [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	186
Total Fixed Income [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	177,727	185,549
Real Assets Fund [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	24,653	24,151
Hancock Horizon Quantitative Long/ Short Fund [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	5,620	5,603
Hancock Horizon Diversified International Fund [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	73,478	62,750
Hancock Horizon Burkenroad Small Cap Fund [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	9,129	9,296
Hancock Horizon Growth Fund [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	29,447	26,469
Hancock Horizon Value Fund [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	29,378	30,321
Equity Securities [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	97,894	84,325
Mineral Interests [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets		1
Total Equity [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	244,946	218,765
Level 1 [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	313,823	254,240
Level 1 [Member] | Cash and Equivalents [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	44,224	10,243
Level 1 [Member] | Total Cash and Cash-Equivalents [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	44,224	10,243
Level 1 [Member] | U.S. Government and Agency Securities [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets		1,082
Level 1 [Member] | Total Fixed Income [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets		1,082
Level 1 [Member] | Real Assets Fund [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	24,653	24,151
Level 1 [Member] | Hancock Horizon Quantitative Long/ Short Fund [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	5,620	5,603
Level 1 [Member] | Hancock Horizon Diversified International Fund [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	73,478	62,750
Level 1 [Member] | Hancock Horizon Burkenroad Small Cap Fund [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	9,129	9,296
Level 1 [Member] | Hancock Horizon Growth Fund [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	29,447	26,469
Level 1 [Member] | Hancock Horizon Value Fund [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	29,378	30,321
Level 1 [Member] | Equity Securities [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	97,894	84,325
Level 1 [Member] | Total Equity [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	244,946	218,764
Level 2 [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	153,184	164,962
Level 2 [Member] | U.S. Government and Agency Securities [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	11,192	14,436
Level 2 [Member] | Municipal Securities [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	31,190	33,980
Level 2 [Member] | Foreign Bonds Notes And Debentures [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	1,743	2,588
Level 2 [Member] | Hancock Horizon Core Bond Fund [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	47,453	51,529
Level 2 [Member] | Corporate Debt Securities [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	61,481	62,429
Level 2 [Member] | Other Fixed Income Securities [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	125
Level 2 [Member] | Total Fixed Income [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	153,184	164,962
Level 3 [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	24,543	19,506
Level 3 [Member] | Emerging Market Debt Fund [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	24,482	19,505
Level 3 [Member] | Other Fixed Income Securities [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	61
Level 3 [Member] | Total Fixed Income [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets	$ 24,543	19,505
Level 3 [Member] | Mineral Interests [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets		1
Level 3 [Member] | Total Equity [Member]
Fair Value Of Pension Plan Assets [Line Items]
Fair value of pension plan assets		$ 1