Employee Benefit Plans - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Total company expenses under the health plan	$ 3,480,000	$ 3,060,000	$ 2,880,000
Deferred compensation Liability	458,000	458,000
Deferred compensation Expense	$ 60,000	$ 60,000	$ 60,000
Common stock held in employer stock fund	410,384	428,785	457,765
Stock Options
Defined Benefit Plan Disclosure [Line Items]
Intrinsic value of options exercised	$ 434,000	$ 20,000	$ 13,000
Unrecognized compensation cost related to nonvested stock options	$ 101,000
Unrecognized compensation cost expected to be recognized over a weighted average period	1 year 1 month 10 days
Restricted Stock
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost expected to be recognized over a weighted average period	2 years 11 days
Unrecognized compensation cost related to nonvested stock awards	$ 447,000
Performance Shares
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost related to nonvested stock awards	$ 0
2012 Plan | Stock Options
Defined Benefit Plan Disclosure [Line Items]
Shares available for potential grants	600,000
Option granted, maximum exercise period	10 years
Vesting period	4 years
2012 Plan | Stock Options | For the first four anniversaries of the grant date
Defined Benefit Plan Disclosure [Line Items]
Percentage of stock award vesting	25.00%
Individual Counterparty
Defined Benefit Plan Disclosure [Line Items]
Stop loss insurance liability	$ 125,000
Aggregate
Defined Benefit Plan Disclosure [Line Items]
Stop loss insurance liability	3,920,000
401 (k) Savings Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Employer Matching Contributions	$ 1,500,000	$ 1,530,000	$ 1,580,000
Supplemental Executive Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan Maximum Employee Contribution As Percentage Of Average Compensation	35.00%
Defined Benefit Plan, Employee Contribution, Age	62 years
Directors Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Employee Contribution, Age	70 years
Defined Contribution Plan Maximum Employee Contribution As Percentage Of Base Salary	100.00%