Goodwill and Intangible Assets (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) $ / loans Rate	Dec. 31, 2017 USD ($) $ / loans Rate	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Servicing Asset at Amortized Cost [Line Items]
Servicing Asset at Amortized Cost	$ 21,396,000	$ 21,945,000	$ 20,415,000	$ 19,351,000
Servicing Asset at Amortized Cost, Additions	5,258,000	7,174,000	5,931,000
Amortization	(5,807,000)	(5,648,000)	(4,958,000)
Valuation Allowance for Impairment of Recognized Servicing Assets, Provisions (Recoveries)	0	(4,000)	(91,000)
Residential Mortgage Loans Serviced	$ 2,950,000,000	$ 2,810,000,000	2,490,000,000
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Prepayment Speed | Rate	9.26%	10.93%
Contractually Specified Servicing Fee, Late Fee, and Ancillary Fee Earned in Exchange for Servicing Financial Asset	$ 7,500,000	$ 7,100,000	5,800,000
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Cost to Service Loans | $ / loans	72.65	64.03
Goodwill [Roll Forward]
Beginning goodwill	$ 150,601,000	$ 150,601,000
Ending goodwill	236,347,000	150,601,000	150,601,000
Finite-lived Intangible Assets [Roll Forward]
Beginning balance	51,151,000	57,625,000
Amortization	(17,165,000)	(17,194,000)
Ending balance	48,232,000	51,151,000	$ 57,625,000
Finite-Lived Intangible Assets [Abstract]
Gross balance	143,007,000	128,761,000
Accumulated amortization	(94,775,000)	(77,610,000)
Carrying value	48,232,000	51,151,000
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
2019	14,964,000
2020	11,729,000
2021	8,706,000
2022	5,805,000
2023 and subsequent	7,028,000
Other servicing rights	2,700,000	0
HomeBancorp Inc.
Goodwill [Roll Forward]
Goodwill acquired	57,616,000	0
Finite-lived Intangible Assets [Roll Forward]
Intangible assets acquired	9,860,000	0
Capital Commerce Bancorp
Goodwill [Roll Forward]
Goodwill acquired	10,680,000	0
Finite-lived Intangible Assets [Roll Forward]
Intangible assets acquired	2,680,000	0
Palmetto Heritage Bancshares
Goodwill [Roll Forward]
Goodwill acquired	17,450,000	0
Finite-lived Intangible Assets [Roll Forward]
Intangible assets acquired	1,706,000	0
Harvest Community Bank
Finite-lived Intangible Assets [Roll Forward]
Intangible assets acquired	0	850,000
Guaranty Bank
Finite-lived Intangible Assets [Roll Forward]
Intangible assets acquired	$ 0	$ 9,870,000
Conventional fixed loans
Servicing Asset at Amortized Cost [Line Items]
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Discount Rate | Rate	9.6851%	9.41%
All loans and leases excluding conventional fixed loans [Member]
Servicing Asset at Amortized Cost [Line Items]
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Discount Rate | Rate	10.6851%	10.41%
Core deposits | Minimum
Goodwill [Roll Forward]
Useful life	1 year
Core deposits | Maximum
Goodwill [Roll Forward]
Useful life	10 years