Fair Value (Details) - Financial Instruments - USD ($) $ in Thousands	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013
Assets:
Cash and due from banks	$ 135,546		$ 117,315
Interest-bearing deposits in other banks	811,287		488,947
Securities held-to-maturity, at amortized cost	24,292		26,555
FHLB and FRB stock	38,748		37,558
Net loans	6,778,722		6,664,159
Federal Deposit Insurance Corporation (FDIC) indemnification asset	7,335	$ 8,540	8,452	$ 10,276	$ 15,537	$ 16,585
Investment in BOLI	207,814		206,498
Liabilities:
Deposits	8,212,671		7,887,758
Borrowed funds	189,036		137,994
Senior and subordinated debt	201,039		200,869
Level 1
Assets:
Cash and due from banks	135,546		117,315
Liabilities:
Senior and subordinated debt	207,356		209,035
Level 2
Assets:
Interest-bearing deposits in other banks	811,287		488,947
Securities held-to-maturity, at amortized cost	24,545		27,670
FHLB and FRB stock	38,748		37,558
Liabilities:
Deposits	8,206,907		7,879,413
Borrowed funds	189,011		137,994
Accrued interest payable	2,189		2,324
Level 3
Assets:
Net loans	6,645,824		6,532,622
Federal Deposit Insurance Corporation (FDIC) indemnification asset	1,663		3,626
Investment in BOLI	207,814		206,498
Accrued interest receivable	26,073		27,506
Other interest-earning assets	2,872		3,904
Carrying Amount | Level 1
Assets:
Cash and due from banks	135,546		117,315
Liabilities:
Senior and subordinated debt	201,039		200,869
Carrying Amount | Level 2
Assets:
Interest-bearing deposits in other banks	811,287		488,947
Securities held-to-maturity, at amortized cost	24,292		26,555
FHLB and FRB stock	38,748		37,558
Liabilities:
Deposits	8,212,671		7,887,758
Borrowed funds	189,036		137,994
Accrued interest payable	2,189		2,324
Carrying Amount | Level 3
Assets:
Net loans	6,778,722		6,664,159
Federal Deposit Insurance Corporation (FDIC) indemnification asset	7,335		8,452
Investment in BOLI	207,814		206,498
Accrued interest receivable	26,073		27,506
Other interest-earning assets	$ 2,810		$ 3,799