Employee Benefits (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Thrift Plan - Defined Contribution [Abstract]
Employee base compensation company match employee contributions (in hundredths)	6.00%
Employer matching rate for employee contributions minimum (in hundredths)	50.00%
Minimum years of service for employees to obtain maximum employer matching (in years)	4 years
Employer matching rate for employee contributions maximum (in hundredths)	200.00%
Maximum years of service for employees to obtain minimum employer matching (in years)	15 years
Non-elective annual contribution for qualified employees	$ 750
Annual base employee compensation to qualify for non-elective employer contributions maximum	40,000
Employer discretionary contribution amount	$ 530,000		$ 605,000		$ 662,000
Vesting period for employer contributions (in years)	5 years
Thrift Plan expenses	$ 22,400,000		20,600,000		18,600,000
Incentive compensation plans [Abstract]
Expense related to cash-based incentive compensation plans	$ 128,100,000		114,300,000		111,700,000
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Interest percentage added to the five-year trailing average of five-year Treasury Securities	1.50%
Interest percentage accrued on employee account balances, Minimum	3.00%
Interest percentage accrued on employee account balances, Maximum	5.00%
Interest percentage accrued on employee account balances for current year	3.00%
Change in projected benefit obligation [Roll Forward]
Projected benefit obligation at beginning of year	$ 38,797,000	[1],[2]	45,224,000
Interest cost	1,309,000		1,487,000
Actuarial loss (gain)	(55,000)		(2,702,000)
Benefits paid	(5,087,000)		(5,212,000)
Projected benefit obligation at end of year	34,964,000	[1],[2]	38,797,000	[1],[2]	45,224,000
Change in plan assets [Roll Forward]
Plan assets at fair value at beginning of year	44,190,000		49,443,000
Actual return on plan assets	2,666,000		(41,000)
Benefits paid	(5,087,000)		(5,212,000)
Plan assets at fair value at end of year	41,769,000		44,190,000		$ 49,443,000
Defined Benefit Plan, Funded Status of Plan [Abstract]
Funded status of the plan	6,805,000		5,393,000
Components of net periodic benefit costs [Abstract]
Interest cost	1,309,000		1,487,000
Expected return on plan assets	(2,167,000)		(2,706,000)
Other	(741,000)		1,849,000
Net periodic pension cost	$ (1,599,000)		$ 630,000
Weighted-average assumptions [Abstract]
Discount rate (in hundredths)	3.43%		3.54%
Expected return on plan assets (in hundredths)	5.00%		5.00%
Estimated Future Benefit Payments [Abstract]
2017	$ 2,706,000
2018	3,072,000
2019	3,402,000
2020	3,090,000
2021	2,934,000
Thereafter	28,044,000
Total estimated future benefit payments	43,248,000
Defined Benefit Plan, Information about Plan Assets [Abstract]
Maximum tax deductible contributions to defined benefit plan	$ 12,000,000
Equity Securities [Member] | Pension Plan [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Percentage of equities and bonds included in portfolio mix of fund used for defined benefit plan (in hundredths)	60.00%
Bonds [Member] | Pension Plan [Member]
Defined Benefit Plan, Information about Plan Assets [Abstract]
Percentage of equities and bonds included in portfolio mix of fund used for defined benefit plan (in hundredths)	40.00%

[1] Projected benefit obligation equals accumulated benefit obligation.

[2] Projected benefit obligation is based on January 1 measurement date.