Reportable Operating Segments - Revision of Prior Period Noninterest Income and Noninterest Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Correction of an Immaterial Error to the Financial Statements
Noninterest income	$ 205,605	$ 226,037	$ 219,111
Noninterest expense	347,554	337,280	327,309
Commercial Banking
Correction of an Immaterial Error to the Financial Statements
Noninterest income	74,236	73,264	78,500
Noninterest expense	68,167	63,193	61,463
Treasury and Other
Correction of an Immaterial Error to the Financial Statements
Noninterest income	40,667	61,190	42,677
Noninterest expense	$ 55,735	62,325	66,538
Restatement adjustment | Misclassifications of noninterest income and noninterest expense | Commercial Banking
Correction of an Immaterial Error to the Financial Statements
Noninterest income		6,900	6,300
Noninterest expense		6,900	6,300
Restatement adjustment | Misclassifications of noninterest income and noninterest expense | Treasury and Other
Correction of an Immaterial Error to the Financial Statements
Noninterest income		1,500	1,400
Noninterest expense		$ 1,500	$ 1,400