Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Summary of Significant Accounting Policies [Abstract]
Minimum number of days past due for nonaccrual loan status	90 days
Period of sustained repayment performance for nonperforming TDRs to be returned to performing status	6 months
Standby letters of credit expiration period	1 year
Noninterest Income [Abstract]
Total noninterest income in-scope of ASC 606	$ 126,012	$ 113,444	$ 111,162
Total noninterest income out-of-scope of ASC 606	(1,250)	7,860	4,551
Total noninterest income	124,762	121,304	115,713
Insurance and Other Financial Services Revenue [Member]
Noninterest Income [Abstract]
Total noninterest income in-scope of ASC 606	24,345	23,532	24,396
Service Charges on Deposit Accounts [Member]
Noninterest Income [Abstract]
Total noninterest income in-scope of ASC 606	17,224	16,750	16,729
ATM and Debit Card Fees [Member]
Noninterest Income [Abstract]
Total noninterest income in-scope of ASC 606	22,699	21,372	19,448
Retirement Plan Administration Fees [Member]
Noninterest Income [Abstract]
Total noninterest income in-scope of ASC 606	26,992	20,213	16,063
Trust [Member]
Noninterest Income [Abstract]
Total noninterest income in-scope of ASC 606	19,524	19,586	18,565
Other [Member]
Noninterest Income [Abstract]
Total noninterest income in-scope of ASC 606	$ 15,228	$ 11,991	$ 15,961