Goodwill and Other Intangible Assets (Core Deposit Intangibles) (Details) - Core Deposit Intangibles - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Impairment write-offs/write downs on the remaining core deposit intangibles		$ 0	$ 0	$ 0
Gross balance		86,099,000	100,166,000
Accumulated amortization		(71,570,000)	(79,112,000)
Net carrying balance		$ 14,529,000	$ 21,054,000
Desert Community Bank
Finite-Lived Intangible Assets [Line Items]
Impairment write-offs/write downs on the remaining core deposit intangibles	$ 1,000,000