Other Income and Other Expense - Other Income and Other Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other income:
Credit-related fee income	$ 77,580	$ 70,424	$ 81,558
Letter of credit fees			52,724
Bank owned life insurance			52,984
Other expense:
Professional services	289,862	268,060	267,540
Amortization of capitalized servicing rights	$ 56,172	$ 50,982	$ 49,906