Fair Value Measurements Fair Value Nonrecurring Basis (Details) - Fair Value, Measurements, Nonrecurring [Member] - USD ($) $ in Thousands		Dec. 31, 2016		Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Receivable, Fair Value Disclosure		$ 3,074	[1]	$ 2,322	[2]
Other Real Estate Owned, Fair Value Disclosure	[3]	1,690
Assets, Fair Value Disclosure		39,541		2,322
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Receivable, Fair Value Disclosure		0	[1]	0	[2]
Other Real Estate Owned, Fair Value Disclosure	[3]	0
Assets, Fair Value Disclosure		0		0
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Receivable, Fair Value Disclosure		0	[1]	0	[2]
Other Real Estate Owned, Fair Value Disclosure	[3]	0
Assets, Fair Value Disclosure		0		0
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Receivable, Fair Value Disclosure		3,074	[1]	2,322	[2]
Other Real Estate Owned, Fair Value Disclosure	[3]	1,690
Assets, Fair Value Disclosure		39,541		2,322
Portion at Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Receivable, Fair Value Disclosure		6,021,611		5,658,254
Portion at Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Receivable, Fair Value Disclosure		0		0
Portion at Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Receivable, Fair Value Disclosure		0		0
Portion at Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Receivable, Fair Value Disclosure		6,021,611		5,658,254
Changes Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Receivable, Fair Value Disclosure		(428)	[1]	(578)	[2]
Other Real Estate Owned, Fair Value Disclosure	[3]	(110)
Assets, Fair Value Disclosure		(10,066)		$ (578)
Wealth Management and Trust Segment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill, Fair Value Disclosure	[4]	34,777
Wealth Management and Trust Segment [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill, Fair Value Disclosure	[4]	0
Wealth Management and Trust Segment [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill, Fair Value Disclosure	[4]	0
Wealth Management and Trust Segment [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill, Fair Value Disclosure	[4]	34,777
Wealth Management and Trust Segment [Member] | Changes Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill, Fair Value Disclosure	[4]	$ (9,528)

[1] Collateral-dependent impaired loans held as of December 31, 2016 that had write-downs in fair value or whose specific reserve changed during 2016.

[2] Collateral-dependent impaired loans held as of December 31, 2015 that had write-downs in fair value or whose specific reserve changed during 2015.

[3] OREO held as of December 31, 2016 that had write-downs in fair value during 2016.

[4] Goodwill balance at Boston Private Wealth as of December 31, 2016 that had write-downs in fair value during 2016. See Part II. Item 8. “Financial Statements and Supplementary Data - Note 8: Goodwill and Other Intangible Assets” for further detail