Junior Subordinated Debentures (Junior Subordinated Debentures) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 464,962
Carrying value, at fair value	278,410	$ 277,155
Junior subordinated debentures, at amortized cost	88,895	$ 100,609
Carrying Value	367,305
Junior Subordinated Debt, at Fair Value
Junior Subordinated Debentures [Line Items]
Issued Amount	379,390
Carrying value, at fair value	278,410
Junior Subordinated Debt, at Fair Value | Umpqua Statutory Trust II
Junior Subordinated Debentures [Line Items]
Issued Amount	20,619
Carrying value, at fair value	$ 17,684
Variable rate basis	LIBOR
Basis spread on LIBOR	3.35%
Effective rate	5.97%
Junior Subordinated Debt, at Fair Value | Umpqua Statutory Trust III
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 30,928
Carrying value, at fair value	$ 26,762
Variable rate basis	LIBOR
Basis spread on LIBOR	3.45%
Effective rate	6.11%
Junior Subordinated Debt, at Fair Value | Umpqua Statutory Trust IV
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 10,310
Carrying value, at fair value	$ 8,332
Variable rate basis	LIBOR
Basis spread on LIBOR	2.85%
Effective rate	5.66%
Junior Subordinated Debt, at Fair Value | Umpqua Statutory Trust V
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 10,310
Carrying value, at fair value	$ 8,232
Variable rate basis	LIBOR
Basis spread on LIBOR	2.85%
Effective rate	6.30%
Junior Subordinated Debt, at Fair Value | Umpqua Master Trust I
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 41,238
Carrying value, at fair value	$ 25,706
Variable rate basis	LIBOR
Basis spread on LIBOR	1.35%
Effective rate	5.57%
Junior Subordinated Debt, at Fair Value | Umpqua Master Trust IB
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 20,619
Carrying value, at fair value	$ 15,786
Variable rate basis	LIBOR
Basis spread on LIBOR	2.75%
Effective rate	6.37%
Junior Subordinated Debt, at Fair Value | Sterling Capital Trust III
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 14,433
Carrying value, at fair value	$ 12,254
Variable rate basis	LIBOR
Basis spread on LIBOR	3.25%
Effective rate	5.92%
Junior Subordinated Debt, at Fair Value | Sterling Capital Trust IV
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 10,310
Carrying value, at fair value	$ 8,597
Variable rate basis	LIBOR
Basis spread on LIBOR	3.15%
Effective rate	5.98%
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	$ 17,306
Variable rate basis	LIBOR
Basis spread on LIBOR	3.25%
Effective rate	6.60%
Junior Subordinated Debt, at Fair Value | Sterling Capital Trust VI
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 10,310
Carrying value, at fair value	$ 8,565
Variable rate basis	LIBOR
Basis spread on LIBOR	3.20%
Effective rate	6.41%
Junior Subordinated Debt, at Fair Value | Sterling Capital Trust VII
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 56,702
Carrying value, at fair value	$ 36,996
Variable rate basis	LIBOR
Basis spread on LIBOR	1.53%
Effective rate	5.59%
Junior Subordinated Debt, at Fair Value | Sterling Capital Trust VIII
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 51,547
Carrying value, at fair value	$ 33,925
Variable rate basis	LIBOR
Basis spread on LIBOR	1.63%
Effective rate	5.70%
Junior Subordinated Debt, at Fair Value | Sterling Capital Trust IX
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 46,392
Carrying value, at fair value	$ 29,426
Variable rate basis	LIBOR
Basis spread on LIBOR	1.40%
Effective rate	4.88%
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	$ 7,701
Variable rate basis	LIBOR
Basis spread on LIBOR	3.15%
Effective rate	6.55%
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	$ 7,185
Variable rate basis	LIBOR
Basis spread on LIBOR	1.80%
Effective rate	5.63%
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	$ 13,953
Variable rate basis	LIBOR
Basis spread on LIBOR	3.75%
Effective rate	6.34%
Junior Subordinated Debt, at Amortized Cost
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 85,572
Junior subordinated debentures, at amortized cost	88,895
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	$ 11,043
Variable rate basis	LIBOR
Basis spread on LIBOR	3.60%
Effective rate	4.91%
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	$ 29,791
Variable rate basis	LIBOR
Basis spread on LIBOR	2.95%
Effective rate	4.35%
Junior Subordinated Debt, at Amortized Cost | CIB Capital Trust
Junior Subordinated Debentures [Line Items]
Issued Amount	$ 10,310
Junior subordinated debentures, at amortized cost	$ 10,945
Variable rate basis	LIBOR
Basis spread on LIBOR	3.45%
Effective rate	4.58%
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	5.35%
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	5.78%
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	4.62%
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	4.62%