Reportable Operating Segments - Revision of Prior Period Noninterest Income and Noninterest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Quantifying Misstatement in Current Year Financial Statements [Line Items]
Noninterest income	$ 47,405	$ 49,664	$ 145,902	$ 151,281
Noninterest expense	93,147	84,784	275,599	257,704
Commercial Banking
Quantifying Misstatement in Current Year Financial Statements [Line Items]
Noninterest income	17,801	17,521	59,264	56,552
Noninterest expense	19,731	16,641	60,575	49,988
Treasury and Other
Quantifying Misstatement in Current Year Financial Statements [Line Items]
Noninterest income	6,928	9,556	19,072	26,142
Noninterest expense	$ 15,347	14,536	$ 44,910	42,701
Restatement adjustment | Misclassifications of noninterest income and noninterest expense | Commercial Banking
Quantifying Misstatement in Current Year Financial Statements [Line Items]
Noninterest income		700		3,300
Noninterest expense		700		3,300
Restatement adjustment | Misclassifications of noninterest income and noninterest expense | Treasury and Other
Quantifying Misstatement in Current Year Financial Statements [Line Items]
Noninterest income		400		1,200
Noninterest expense		$ 400		$ 1,200