Business Combination (Details) (USD $)	3 Months Ended	6 Months Ended					3 Months Ended		3 Months Ended	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Dec. 31, 2011	May 10, 2013 Boston Private [Member]	Mar. 31, 2013 American Heritage Holdings [Member]	Feb. 28, 2013 American Heritage Holdings [Member]	Jun. 30, 2012 First Independent Bank [Member]	Jun. 30, 2013 First Independent Bank [Member]	Jun. 30, 2012 First Independent Bank [Member]	Feb. 29, 2012 First Independent Bank [Member]	Feb. 28, 2013 Evidence of Credit Deterioration [Member]	Feb. 29, 2012 Evidence of Credit Deterioration [Member]	May 10, 2013 No Evidence of credit deterioration [Member]	Feb. 28, 2013 No Evidence of credit deterioration [Member]	Feb. 29, 2012 No Evidence of credit deterioration [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Recurring [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Recurring [Member]
Business Acquisition, Cost of Acquired Entity, Purchase Price [Abstract]
Business Combination, Consideration Transferred								$ 6,500,000
Business Combination, Consideration Transferred, Other								2,200,000
Cash paid						122,985,000		8,749,000				28,900,000
Bargain purchase gain		7,544,000	0				7,544,000
Net purchase price												40,600,000
Contingent consideration	13,292,000		13,292,000	15,442,000	0							11,700,000						9,868,000	15,442,000
Contingent consideration paid		(6,838,000)	0							(6,800,000)
Business Acquisition, Purchase Price Allocation, Noncurrent Assets [Abstract]
Cash and cash equivalents						340,000		15,626,000				150,045,000
Investments and MBS								1,030,000				187,465,000
Loans receivable, net						273,353,000		97,262,000				349,990,000
Goodwill	22,577,000	36,633,000	22,577,000	22,577,000	0	14,056,000						22,577,000
Core deposit intangible						1,674,000		453,000				11,974,000
Fixed assets												4,038,000
Other assets						2,721,000		27,197,000				10,886,000
Total assets acquired						292,144,000		141,568,000				736,975,000
Deposits						168,246,000		118,221,000				695,919,000
Other Liabilties						913,000		7,054,000				409,000
Total liabilities assumed						169,159,000		125,275,000				696,328,000
Net assets acquired								16,293,000				40,647,000
Contractual cash flows													16,100,000	24,400,000
Expected cash flows													13,600,000	17,200,000
Present value of expected cash flows													(11,900,000)	(15,300,000)
Loan Principal Guaranteed By Government Agencies													9,800,000
Unpaid principal balance and contractual interest															280,700,000	83,300,000	403,800,000
Cash flows not expected to be collected															3,500,000	3,900,000	12,700,000
Discount on acquired loans															5,100,000	4,500,000	21,800,000
Business Acquisition, Pro Forma Information [Abstract]
Net interest income	78,910,000		159,744,000						7,859,000		11,100,000
Noninterest income	44,741,000		77,333,000						1,678,000		2,181,000
Net income	$ 320,886,000		$ 338,391,000						$ 3,901,000		$ 6,008,000
Earnings per share - basic	$ 5.17		$ 5.45						$ 0.06		$ 0.10
Earnings per share - diluted	$ 5.13		$ 5.40						$ 0.06		$ 0.10