Junior Subordinated Debentures (Junior Subordinated Debentures) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Junior Subordinated Debentures [Line Items]
Issued amount	$ 475,427
Carrying value, at amortized cost	100,609	$ 100,931
Carrying value	377,764
Junior Subordinated Debt, at Fair Value
Junior Subordinated Debentures [Line Items]
Issued amount	379,390
Carrying value, at fair value	277,155
Junior Subordinated Debt, at Fair Value | Umpqua Statutory Trust II
Junior Subordinated Debentures [Line Items]
Issued amount	20,619
Carrying value, at fair value	$ 17,545
Variable rate basis	LIBOR
Basis spread on LIBOR	3.35%
Effective rate	5.56%
Junior Subordinated Debt, at Fair Value | Umpqua Statutory Trust III
Junior Subordinated Debentures [Line Items]
Issued amount	$ 30,928
Carrying value, at fair value	$ 26,586
Variable rate basis	LIBOR
Basis spread on LIBOR	3.45%
Effective rate	5.66%
Junior Subordinated Debt, at Fair Value | Umpqua Statutory Trust IV
Junior Subordinated Debentures [Line Items]
Issued amount	$ 10,310
Carrying value, at fair value	$ 8,232
Variable rate basis	LIBOR
Basis spread on LIBOR	2.85%
Effective rate	5.27%
Junior Subordinated Debt, at Fair Value | Umpqua Statutory Trust V
Junior Subordinated Debentures [Line Items]
Issued amount	$ 10,310
Carrying value, at fair value	$ 8,207
Variable rate basis	LIBOR
Basis spread on LIBOR	2.85%
Effective rate	5.59%
Junior Subordinated Debt, at Fair Value | Umpqua Master Trust I
Junior Subordinated Debentures [Line Items]
Issued amount	$ 41,238
Carrying value, at fair value	$ 25,674
Variable rate basis	LIBOR
Basis spread on LIBOR	1.35%
Effective rate	4.72%
Junior Subordinated Debt, at Fair Value | Umpqua Master Trust IB
Junior Subordinated Debentures [Line Items]
Issued amount	$ 20,619
Carrying value, at fair value	$ 15,800
Variable rate basis	LIBOR
Basis spread on LIBOR	2.75%
Effective rate	5.66%
Junior Subordinated Debt, at Fair Value | Sterling Capital Trust III
Junior Subordinated Debentures [Line Items]
Issued amount	$ 14,433
Carrying value, at fair value	$ 12,120
Variable rate basis	LIBOR
Basis spread on LIBOR	3.25%
Effective rate	5.51%
Junior Subordinated Debt, at Fair Value | Sterling Capital Trust IV
Junior Subordinated Debentures [Line Items]
Issued amount	$ 10,310
Carrying value, at fair value	$ 8,550
Variable rate basis	LIBOR
Basis spread on LIBOR	3.15%
Effective rate	5.51%
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	5.87%
Junior Subordinated Debt, at Fair Value | Sterling Capital Trust VI
Junior Subordinated Debentures [Line Items]
Issued amount	$ 10,310
Carrying value, at fair value	$ 8,586
Variable rate basis	LIBOR
Basis spread on LIBOR	3.20%
Effective rate	5.75%
Junior Subordinated Debt, at Fair Value | Sterling Capital Trust VII
Junior Subordinated Debentures [Line Items]
Issued amount	$ 56,702
Carrying value, at fair value	$ 36,942
Variable rate basis	LIBOR
Basis spread on LIBOR	1.53%
Effective rate	4.78%
Junior Subordinated Debt, at Fair Value | Sterling Capital Trust VIII
Junior Subordinated Debentures [Line Items]
Issued amount	$ 51,547
Carrying value, at fair value	$ 33,891
Variable rate basis	LIBOR
Basis spread on LIBOR	1.63%
Effective rate	4.90%
Junior Subordinated Debt, at Fair Value | Sterling Capital Trust IX
Junior Subordinated Debentures [Line Items]
Issued amount	$ 46,392
Carrying value, at fair value	$ 29,089
Variable rate basis	LIBOR
Basis spread on LIBOR	1.40%
Effective rate	4.36%
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	$ 7,712
Variable rate basis	LIBOR
Basis spread on LIBOR	3.15%
Effective rate	5.80%
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	$ 7,083
Variable rate basis	LIBOR
Basis spread on LIBOR	1.80%
Effective rate	4.93%
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	$ 13,832
Variable rate basis	LIBOR
Basis spread on LIBOR	3.75%
Effective rate	5.82%
Junior Subordinated Debt, at Amortized Cost
Junior Subordinated Debentures [Line Items]
Issued amount	$ 96,037
Carrying value, at amortized cost	100,609
Junior Subordinated Debt, at Amortized Cost | HB Capital Trust I
Junior Subordinated Debentures [Line Items]
Issued amount	5,310
Carrying value, at amortized cost	$ 5,994
Stated interest rate	10.875%
Effective rate	8.70%
Junior Subordinated Debt, at Amortized Cost | Humboldt Bancorp Statutory Trust I
Junior Subordinated Debentures [Line Items]
Issued amount	$ 5,155
Carrying value, at amortized cost	$ 5,664
Stated interest rate	10.20%
Effective rate	8.59%
Junior Subordinated Debt, at Amortized Cost | Humboldt Bancorp Statutory Trust II
Junior Subordinated Debentures [Line Items]
Issued amount	$ 10,310
Carrying value, at amortized cost	$ 11,056
Variable rate basis	LIBOR
Basis spread on LIBOR	3.60%
Effective rate	4.36%
Junior Subordinated Debt, at Amortized Cost | Humboldt Bancorp Statutory Trust III
Junior Subordinated Debentures [Line Items]
Issued amount	$ 27,836
Carrying value, at amortized cost	$ 29,823
Variable rate basis	LIBOR
Basis spread on LIBOR	2.95%
Effective rate	3.81%
Junior Subordinated Debt, at Amortized Cost | CIB Capital Trust
Junior Subordinated Debentures [Line Items]
Issued amount	$ 10,310
Carrying value, at amortized cost	$ 10,956
Variable rate basis	LIBOR
Basis spread on LIBOR	3.45%
Effective rate	4.18%
Junior Subordinated Debt, at Amortized Cost | Western Sierra Statutory Trust I
Junior Subordinated Debentures [Line Items]
Issued amount	$ 6,186
Carrying value, at amortized cost	$ 6,186
Variable rate basis	LIBOR
Basis spread on LIBOR	3.58%
Effective rate	4.96%
Junior Subordinated Debt, at Amortized Cost | Western Sierra Statutory Trust II
Junior Subordinated Debentures [Line Items]
Issued amount	$ 10,310
Carrying value, at amortized cost	$ 10,310
Variable rate basis	LIBOR
Basis spread on LIBOR	3.60%
Effective rate	5.20%
Junior Subordinated Debt, at Amortized Cost | Western Sierra Statutory Trust III
Junior Subordinated Debentures [Line Items]
Issued amount	$ 10,310
Carrying value, at amortized cost	$ 10,310
Variable rate basis	LIBOR
Basis spread on LIBOR	2.90%
Effective rate	4.26%
Junior Subordinated Debt, at Amortized Cost | Western Sierra Statutory Trust IV
Junior Subordinated Debentures [Line Items]
Issued amount	$ 10,310
Carrying value, at amortized cost	$ 10,310
Variable rate basis	LIBOR
Basis spread on LIBOR	2.90%
Effective rate	4.26%