Employee Compensation and Benefit Plans - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Employee Home Ownership Plan | 12 month LIBOR
Employee Benefits Disclosure [Line Items]
Basis spread on EHOP loans	2.25%
Defined Contribution Plan, The 401(k) Plan
Employee Benefits Disclosure [Line Items]
Maximum percentage of pre-tax income employees are allowed to contribute towards 401(k) plan	75.00%
Maximum annual amount allowable for employee contributions	$ 18,500	$ 18,000	$ 18,000
Maximum percentage of employer matching contributions towards 401(k) plan	5.00%
Deferred Compensation Plan
Employee Benefits Disclosure [Line Items]
Maximum percentage of base salary that may be deferred under the DC Plan	50.00%
Maximum percentage of eligible bonus payment that may be deferred under the DC Plan	100.00%
Deferrals under the DC Plan	$ 5,500,000		4,400,000
DC Plan investment gains	$ 1,700,000	$ 4,700,000	$ 2,400,000
Employee Stock Ownership Plan (ESOP), Plan
Employee Benefits Disclosure [Line Items]
Maximum percentage of employee's eligible pay earned in the fiscal year contributed by the company in cash or common stock towards ESOP	10.00%
ESOP contributions vesting period	5 years
Employee Home Ownership Plan
Employee Benefits Disclosure [Line Items]
Amortization period	30 years
EHOP loan term, option one	5 years
EHOP loan term, option two	7 years
EHOP loan term, option three	10 years
Maximum loan amount percentage lesser of purchase price or the appraised value	80.00%