Dispositions and Held-for-Sale (Dispositions) (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Mar. 17, 2018 USD ($) banking_branch
Disposition [Line Items]
Net gain on sale of business	$ 0	$ 3,807	$ 31,470	$ 3,807
East West Insurance Services, Inc.
Disposition [Line Items]
Proceeds from sale of business		4,300
Net gain on sale of business		$ 3,800
Desert Community Bank
Disposition [Line Items]
Net gain on sale of business			31,500
Net cash payment in sale of branches			$ 499,900
Desert Community Bank | California
Disposition [Line Items]
Number of branches sold | banking_branch					8
Loans | Desert Community Bank
Disposition [Line Items]
Branch assets sold					$ 59,100
Cash and cash equivalents | Desert Community Bank
Disposition [Line Items]
Branch assets sold					9,000
Premises and equipment | Desert Community Bank
Disposition [Line Items]
Branch assets sold					7,900
Deposits | Desert Community Bank
Disposition [Line Items]
Branch liabilities sold					$ 613,700