Fair Value Measurements - Additional Information (Details)	Sep. 30, 2017 executive employee InsurancePolicy
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of employees with SERP account balances | employee	4
Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of life insurance policies | InsurancePolicy	2
Number of former executives | executive	2
Nonqualified Deferred Compensation Plan [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Percentage of compensation eligible to be deferred	50.00%