Parent Company Financial Information - Statements of Condition (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Assets:
Allowance for loan losses	$ (200,307)	$ (180,424)	$ (189,555)	$ (202,068)
Investments in subsidiaries:
Other assets	2,046,338	1,802,939
Total assets	43,310,900	40,832,258
Liabilities and equity:
Term borrowings	791,368	1,170,963
Total liabilities	38,234,892	36,046,878
Total equity	5,076,008	4,785,380	$ 4,580,488	$ 2,705,084
Total liabilities and equity	43,310,900	40,832,258
Parent Company
Assets:
Cash	369,268	334,485
Notes receivable	2,716	2,888
Allowance for loan losses	0	(925)
Investments in subsidiaries:
Bank	5,038,909	4,741,105
Non-bank	17,892	20,281
Other assets	171,121	180,757
Total assets	5,599,906	5,278,591
Liabilities and equity:
Accrued employee benefits and other liabilities	177,080	158,648
Term borrowings	642,249	629,994
Total liabilities	819,329	788,642
Total equity	4,780,577	4,489,949
Total liabilities and equity	$ 5,599,906	$ 5,278,591