Reportable Operating Segments - Revision of Prior Period Noninterest Income and Noninterest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Correction of an Immaterial Error to the Financial Statements
Noninterest income	$ 49,797	$ 50,558	$ 98,497	$ 101,617
Noninterest expense	91,865	86,929	182,452	172,920
Commercial Banking
Correction of an Immaterial Error to the Financial Statements
Noninterest income	21,463	20,197	41,463	39,031
Noninterest expense	21,196	17,034	40,844	33,347
Treasury and Other
Correction of an Immaterial Error to the Financial Statements
Noninterest income	6,176	7,980	12,144	16,586
Noninterest expense	$ 15,085	13,727	$ 29,563	28,165
Restatement adjustment | Misclassifications of noninterest income and noninterest expense | Commercial Banking
Correction of an Immaterial Error to the Financial Statements
Noninterest income		1,300		2,500
Noninterest expense		1,300		2,500
Restatement adjustment | Misclassifications of noninterest income and noninterest expense | Treasury and Other
Correction of an Immaterial Error to the Financial Statements
Noninterest income		400		800
Noninterest expense		$ 400		$ 800