Borrowings - Other Borrowings (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Long-term borrowings:
Amount	$ 397,845	$ 597,847
Weighted Average Rate	1.56%	1.63%
Total borrowings	$ 2,712,442	$ 1,765,894
Total short-term and long-term borrowings, Weighted Average Rate	1.14%	0.89%
FHLB advances: 1.20% - 1.22% fixed-rate notes | Minimum
Long-term borrowings:
Stated interest rate	1.20%
FHLB advances: 1.20% - 1.22% fixed-rate notes | Maximum
Long-term borrowings:
Stated interest rate	1.22%
FHLB Advances | FHLB advances: 0.92% - 7.44% fixed-rate notes due 2017 to 2020
Long-term borrowings:
Amount	$ 339,255	$ 438,538
Weighted Average Rate	1.28%	1.24%
Advances payable from Federal Home Loan Banks	$ 338,900	$ 437,800
Purchase accounting premiums	$ 400	700
FHLB Advances | FHLB advances: 0.92% - 7.44% fixed-rate notes due 2017 to 2020 | Minimum
Long-term borrowings:
Stated interest rate	0.92%
FHLB Advances | FHLB advances: 0.92% - 7.44% fixed-rate notes due 2017 to 2020 | Maximum
Long-term borrowings:
Stated interest rate	7.44%
Securities sold under agreements to repurchase
Long-term borrowings:
Amount	$ 3,000
Securities sold under agreements to repurchase | Securities sold under agreements to repurchase: 1.48% - 2.75% fixed-rate notes due in 2017
Long-term borrowings:
Amount	$ 3,005	$ 19,144
Weighted Average Rate	2.75%	3.17%
Purchase accounting premiums	$ 5	$ 100
Advances payable	$ 3,000	19,000
Securities sold under agreements to repurchase | Securities sold under agreements to repurchase: 1.48% - 2.75% fixed-rate notes due in 2017 | Minimum
Long-term borrowings:
Stated interest rate	1.48%
Securities sold under agreements to repurchase | Securities sold under agreements to repurchase: 1.48% - 2.75% fixed-rate notes due in 2017 | Maximum
Long-term borrowings:
Stated interest rate	2.75%
Line of credit
Long-term borrowings:
Amount	$ 39,914	$ 124,625
Weighted Average Rate	2.98%	2.52%
Spread on variable rate	1.75%
Subordinated debt obligations | Subordinated debt obligations: floating-rate based on three-month LIBOR plus 1.45% - 2.85% due 2034 to 2035
Long-term borrowings:
Amount	$ 11,390	$ 11,285
Weighted Average Rate	3.49%	3.14%
Advances payable	$ 15,000	$ 15,000
Purchase accounting discounts	$ 3,600	3,700
Subordinated debt obligations | Subordinated debt obligations: floating-rate based on three-month LIBOR plus 1.45% - 2.85% due 2034 to 2035 | Minimum
Long-term borrowings:
Spread on variable rate	1.45%
Subordinated debt obligations | Subordinated debt obligations: floating-rate based on three-month LIBOR plus 1.45% - 2.85% due 2034 to 2035 | Maximum
Long-term borrowings:
Spread on variable rate	2.85%
Subordinated debt obligations | Subordinated debt obligations: floating-rate based on three-month LIBOR plus 3.25% due in 2032
Long-term borrowings:
Amount	$ 4,281	$ 4,255
Weighted Average Rate	4.55%	4.25%
Spread on variable rate	3.25%
Advances payable	$ 5,000	$ 5,000
Purchase accounting discounts	700	700
Securities sold under agreements to repurchase
Short-term borrowings:
Amount	$ 414,597	$ 343,047
Weighted Average Rate	0.44%	0.16%
FHLB Advances | FHLB advances: 1.20% - 1.22% fixed-rate notes
Short-term borrowings:
Amount	$ 1,900,000	$ 825,000
Weighted Average Rate	1.21%	0.65%