Employee Benefit Plans (Details)		1 Months Ended	12 Months Ended
	Feb. 08, 2018	Feb. 28, 2018	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) shares
Share-based Payment Arrangement [Abstract]
Employer matching contribution, percent of match for first 3% of compensation			100.00%
Employer matching contribution, percent of employees' gross pay, first 3%			3.00%
Employer matching contribution, percent of match for the next 2% of compensation			50.00%
Employer matching contribution, percent of employees' gross pay, next 2%			2.00%
Employer matching contribution, percent of match total			4.00%
Employer matching contribution, percent of employees' gross pay total			5.00%
Employee stock ownership plan, contribution expense			$ 10,280,000	$ 13,021,000	$ 10,769,000
Deferred compensation expense			$ 2,716,000	2,294,000	2,309,000
Defined Contribution Plan Disclosure [Line Items]
Purchase price of common stock (as percent)			95.00%
Stock split, conversion ratio	2	2
Allocated stock-based compensation expense			$ 13,197,000	$ 12,921,000	$ 11,227,000
Compensation not yet recognized, stock options			0
Compensation not yet recognized, share-based awards other than options			$ 15,524,000
Compensation cost not yet recognized, period for recognition			1 year 8 months 12 days
Options outstanding, intrinsic value			$ 134,000
Share price (in dollars per share) | $ / shares			$ 21.59
Options, exercises in period | shares			900	3,050	111,728
Options, exercises in period, intrinsic value			$ 10,000	$ 43,000	$ 561,000
Options, grants in period, gross | shares			0	0	0
Employee Stock Purchase Plan 2015
Defined Contribution Plan Disclosure [Line Items]
Maximum annual contributions per employee, amount			$ 25,000
Service period			6 months
Special Employee Stock Purchase Plan 2015
Defined Contribution Plan Disclosure [Line Items]
Maximum annual contributions per employee, amount			$ 10,000
Purchase price of common stock (as percent)			85.00%