Fair Value - Carrying Amounts and Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity	$ 1,158,643	$ 1,187,818
Net LHFI	7,779,948	7,023,766
FDIC indemnification asset	0	738
Deposits	10,056,012	9,588,230
Long-term FHLB advances	251,049	501,155
Subordinated notes	0	49,969
Junior subordinated debt securities	61,856	61,856
Level 2 [Member] | Carrying Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and short-term investments	328,206	278,001
Securities held to maturity	1,158,643	1,187,818
Deposits	10,056,012	9,588,230
Short-term liabilities	1,309,595	853,659
Long-term FHLB advances	251,049	501,155
Subordinated notes	0	49,969
Junior subordinated debt securities	61,856	61,856
Level 2 [Member] | Estimate Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and short-term investments	328,206	278,001
Securities held to maturity	1,157,046	1,195,367
Deposits	10,059,794	9,592,531
Short-term liabilities	1,309,595	853,659
Long-term FHLB advances	251,050	501,160
Subordinated notes	0	51,405
Junior subordinated debt securities	41,057	49,021
Level 3 [Member] | Carrying Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net LHFI	7,779,948	7,023,766
Acquired loans	260,850	378,419
FDIC indemnification asset	0	738
Level 3 [Member] | Estimate Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net LHFI	7,825,009	7,136,105
Acquired loans	260,850	378,419
FDIC indemnification asset	$ 0	$ 738