Junior Subordinated Debentures (Junior Subordinated Debentures) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 464,962
Carrying value, at fair value	282,846	$ 277,155
Junior subordinated debentures, at amortized cost	88,781	$ 100,609
Carrying Value	371,627
Junior Subordinated Debt, at Fair Value
Junior Subordinated Debentures [Line Items]
Issued Amount	379,390
Carrying value, at fair value	282,846
Junior Subordinated Debt, at Fair Value | Umpqua Statutory Trust II
Junior Subordinated Debentures [Line Items]
Issued Amount	20,619
Carrying value, at fair value	$ 17,808
Variable rate basis	LIBOR
Basis spread on LIBOR	3.35%
Effective rate	6.59%
Junior Subordinated Debt, at Fair Value | Umpqua Statutory Trust III
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 30,928
Carrying value, at fair value	$ 26,933
Variable rate basis	LIBOR
Basis spread on LIBOR	3.45%
Effective rate	6.62%
Junior Subordinated Debt, at Fair Value | Umpqua Statutory Trust IV
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 10,310
Carrying value, at fair value	$ 8,420
Variable rate basis	LIBOR
Basis spread on LIBOR	2.85%
Effective rate	6.35%
Junior Subordinated Debt, at Fair Value | Umpqua Statutory Trust V
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 10,310
Carrying value, at fair value	$ 8,297
Variable rate basis	LIBOR
Basis spread on LIBOR	2.85%
Effective rate	6.44%
Junior Subordinated Debt, at Fair Value | Umpqua Master Trust I
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 41,238
Carrying value, at fair value	$ 26,446
Variable rate basis	LIBOR
Basis spread on LIBOR	1.35%
Effective rate	5.74%
Junior Subordinated Debt, at Fair Value | Umpqua Master Trust IB
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 20,619
Carrying value, at fair value	$ 15,979
Variable rate basis	LIBOR
Basis spread on LIBOR	2.75%
Effective rate	6.56%
Junior Subordinated Debt, at Fair Value | Sterling Capital Trust III
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 14,433
Carrying value, at fair value	$ 12,355
Variable rate basis	LIBOR
Basis spread on LIBOR	3.25%
Effective rate	6.53%
Junior Subordinated Debt, at Fair Value | Sterling Capital Trust IV
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 10,310
Carrying value, at fair value	$ 8,671
Variable rate basis	LIBOR
Basis spread on LIBOR	3.15%
Effective rate	6.50%
Junior Subordinated Debt, at Fair Value | Sterling Capital Statutory Trust V
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 20,619
Carrying value, at fair value	$ 17,410
Variable rate basis	LIBOR
Basis spread on LIBOR	3.25%
Effective rate	6.66%
Junior Subordinated Debt, at Fair Value | Sterling Capital Trust VI
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 10,310
Carrying value, at fair value	$ 8,616
Variable rate basis	LIBOR
Basis spread on LIBOR	3.20%
Effective rate	6.62%
Junior Subordinated Debt, at Fair Value | Sterling Capital Trust VII
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 56,702
Carrying value, at fair value	$ 37,908
Variable rate basis	LIBOR
Basis spread on LIBOR	1.53%
Effective rate	5.77%
Junior Subordinated Debt, at Fair Value | Sterling Capital Trust VIII
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 51,547
Carrying value, at fair value	$ 34,739
Variable rate basis	LIBOR
Basis spread on LIBOR	1.63%
Effective rate	5.88%
Junior Subordinated Debt, at Fair Value | Sterling Capital Trust IX
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 46,392
Carrying value, at fair value	$ 30,354
Variable rate basis	LIBOR
Basis spread on LIBOR	1.40%
Effective rate	5.71%
Junior Subordinated Debt, at Fair Value | Lynnwood Financial Statutory Trust I
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 9,279
Carrying value, at fair value	$ 7,751
Variable rate basis	LIBOR
Basis spread on LIBOR	3.15%
Effective rate	6.61%
Junior Subordinated Debt, at Fair Value | Lynnwood Financial Statutory Trust II
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 10,310
Carrying value, at fair value	$ 7,236
Variable rate basis	LIBOR
Basis spread on LIBOR	1.80%
Effective rate	5.89%
Junior Subordinated Debt, at Fair Value | Klamath First Capital Trust I
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 15,464
Carrying value, at fair value	$ 13,923
Variable rate basis	LIBOR
Basis spread on LIBOR	3.75%
Effective rate	6.98%
Junior Subordinated Debt, at Amortized Cost
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 85,572
Junior subordinated debentures, at amortized cost	88,781
Junior Subordinated Debt, at Amortized Cost | Humboldt Bancorp Statutory Trust II
Junior Subordinated Debentures [Line Items]
Issued Amount	10,310
Junior subordinated debentures, at amortized cost	$ 11,016
Variable rate basis	LIBOR
Basis spread on LIBOR	3.60%
Effective rate	5.07%
Junior Subordinated Debt, at Amortized Cost | Humboldt Bancorp Statutory Trust III
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 27,836
Junior subordinated debentures, at amortized cost	$ 29,726
Variable rate basis	LIBOR
Basis spread on LIBOR	2.95%
Effective rate	4.51%
Junior Subordinated Debt, at Amortized Cost | CIB Capital Trust
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 10,310
Junior subordinated debentures, at amortized cost	$ 10,923
Variable rate basis	LIBOR
Basis spread on LIBOR	3.45%
Effective rate	5.04%
Junior Subordinated Debt, at Amortized Cost | Western Sierra Statutory Trust I
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 6,186
Junior subordinated debentures, at amortized cost	$ 6,186
Variable rate basis	LIBOR
Basis spread on LIBOR	3.58%
Effective rate	5.92%
Junior Subordinated Debt, at Amortized Cost | Western Sierra Statutory Trust II
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 10,310
Junior subordinated debentures, at amortized cost	$ 10,310
Variable rate basis	LIBOR
Basis spread on LIBOR	3.60%
Effective rate	5.94%
Junior Subordinated Debt, at Amortized Cost | Western Sierra Statutory Trust III
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 10,310
Junior subordinated debentures, at amortized cost	$ 10,310
Variable rate basis	LIBOR
Basis spread on LIBOR	2.90%
Effective rate	5.24%
Junior Subordinated Debt, at Amortized Cost | Western Sierra Statutory Trust IV
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 10,310
Junior subordinated debentures, at amortized cost	$ 10,310
Variable rate basis	LIBOR
Basis spread on LIBOR	2.90%
Effective rate	5.24%