Reportable Operating Segments - Revision of Prior Period Noninterest Income and Noninterest Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Correction of an Immaterial Error to the Financial Statements
Noninterest income	$ 48,700	$ 51,059
Noninterest expense	90,587	85,991
Commercial Banking
Correction of an Immaterial Error to the Financial Statements
Noninterest income	20,000	18,834
Noninterest expense	19,648	16,313
Treasury and Other
Correction of an Immaterial Error to the Financial Statements
Noninterest income	5,968	8,606
Noninterest expense	$ 14,478	14,438
Restatement adjustment | Misclassifications of noninterest income and noninterest expense | Commercial Banking
Correction of an Immaterial Error to the Financial Statements
Noninterest income		1,300
Noninterest expense		1,300
Restatement adjustment | Misclassifications of noninterest income and noninterest expense | Treasury and Other
Correction of an Immaterial Error to the Financial Statements
Noninterest income		400
Noninterest expense		$ 400