Employee Benefit Plans - Additional Information (Details)	3 Months Ended
	Mar. 31, 2019 USD ($) Hour Installment Director	Mar. 31, 2018 USD ($) Director	Dec. 31, 2018 USD ($)
401(k) Plan [Abstract]
Minimum age to participate	18 years
Minimum working hours to participate | Hour	20
Annual contribution per employee	100.00%
Employer matching contribution percentage on first 6% of deferred compensation	100.00%
Percent of employee's compensation deferred that receives company match	6.00%
Additional safe harbor contribution by employer, percent	3.00%
401(k) expenses	$ 231,000,000	$ 172,000,000
Deferred Compensation Plan [Abstract]
Number of directors participating in Deferred Compensation Plan | Director	0	0
Bank-owned life insurance	$ 93,000	$ 89,000
Accrued liability for deferred compensation program	111,000,000		$ 103,000,000
Former Key Employee [Member]
Deferred Compensation Plan [Abstract]
Deferred compensation expense	16,000,000	13,000,000
Bank-owned life insurance	7,100,000	7,100,000
Cash surrender value of life insurance policies	$ 1,400,000		$ 1,400,000
Maximum [Member]
401(k) Plan [Abstract]
Employer matching contribution	6.00%
Deferred Compensation Plan [Abstract]
Number of installments for contributions | Installment	5
Minimum [Member]
Deferred Compensation Plan [Abstract]
Number of installments for contributions | Installment	1
Supplemental Executive Retirement Plan [Member]
Supplemental Executive Retirement Plan [Abstract]
Pension liability	$ 2,800,000	2,700,000
Pension expense	$ 73,000	$ 73,000