Employee Benefit and Deferred Compensation Plans - Additional Information (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) point plan shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2007 officer
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated benefit obligation	$ 24,945,000	$ 27,859,000
Retiring age limit, minimum	55 years
Retiring age limit, maximum	65 years
Eligible employee from service (in years)	15 years
Number of points for eligibility (points) | point	70
Minimum eligible age for Medicare coverage	65 years
Life insurance coverage face value	$ 5,000
Life insurance maturity age	70 years
Additional life insurance maturity age	70 years
Expected company contributions	$ 156,000
Health care cost trend rate (percent)	5.60%
Percentage of plan compensation as nondiscretionary contribution (percent)	5.00%
Percentage of plan compensation in excess of social security wage base (percent)	5.00%
Hours of service credited to the employees during the year	1000 hours
Redemption notice	60 days
Employee deferrals (percent)	4.00%
Employee deferrals amounts	$ 13,477,000	11,471,000	$ 10,762,000
Number of officers provided for | officer				4
Expiration period subsequent to retirement				15 years
Supplemental executive retirement liabilities totaled	$ 3,865,000	3,846,000
Number of conventional deferred compensation plans | plan	2
Company's deferred compensation plan expense	$ 1,290,000	1,935,000	1,537,000
Incentive compensation plan expense	$ 5,117,000	$ 4,490,000	$ 2,307,000
Option expiration period	10 years
Granted (shares) | shares	0	0	0
Intrinsic value of options exercised	$ 1,180,000	$ 2,487,000	$ 8,323,000
Fair value of options vested in period			78,000
Common shares reserved for issuance under employee benefit plans (shares) | shares	2,043,402
Stock compensation plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Compensation expense	$ 0	0	0
Unrecognized stock-based compensation expense	0
Performance- Based Restricted Stock
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Compensation expense	7,251,000	5,293,000	3,117,000
Time- Based Restricted Stock
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Unrecognized stock-based compensation expense	$ 7,909,000
Weighted average period over which unrecognized expense is expected to be recognized (in years)	1 year 5 months 13 days
Growth Investment
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Equity income strategy (percent)	55.00%
Real Estate | Growth Investment
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Equity income strategy (percent)	5.00%
Interest Rate Contract | Growth Investment
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Equity income strategy (percent)	45.00%
Minimum | Equity Securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Equity income strategy (percent)	65.00%
Minimum | Debt Securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Equity income strategy (percent)	25.00%
Maximum | Equity Securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Equity income strategy (percent)	75.00%
Maximum | Debt Securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Equity income strategy (percent)	35.00%
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Company contribution to pension benefit plan	$ 0	0
Accumulated benefit obligation	24,945,000	27,859,000	$ 28,012,000
Other Postretirement Benefits Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Company contribution to pension benefit plan	$ 89,000	$ 119,000