Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Assets, Fair Value Disclosure [Abstract]
Alternative investments	$ 24,400	$ 8,300
Assets and liabilities measured at fair value on a nonrecurring basis [Abstract]
Valuation allowance of impaired loans	2,300	1,100
Other Liabilities [Member]
Assets measured on recurring basis, unobservable input reconciliation, calculation [Roll Forward]
Fair value, beginning of period	0	0
Total realized gains included in income	0	0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	0	0
Purchases	0	0
Issuances	0	0
Settlements	0	0
Transfers out of Level 3	0	0
Fair value, September 30	0	0
Total realized gains included in income related to financial assets and liabilities still on the consolidated balance sheet at period end	0	0
Fair Value, Measurements, Recurring [Member]
Assets, Fair Value Disclosure [Abstract]
U.S. treasury securities	30,445	250
U.S. government agency securities	180,801	21,769
Mortgage-backed securities	1,263,819	976,626
State and municipal securities	784,612	212,720
Asset-Backed Securities, at Carrying Value	173,292	78,580
Corporate notes and other	82,314	8,601
Total investment securities available-for-sale	2,515,283	1,298,546
Alternative investments	28,874	10,478
Other assets	11,812	13,340
Total assets at fair value	2,555,969	1,322,364
Liabilities at fair value [Abstract]
Other liabilities	13,886	15,758
Total liabilities at fair value	13,886	15,758
Fair Value, Measurements, Recurring [Member] | Quoted Market Prices in an Active Market (Level 1) [Member]
Assets, Fair Value Disclosure [Abstract]
U.S. treasury securities	0	0
U.S. government agency securities	0	0
Mortgage-backed securities	0	0
State and municipal securities	0	0
Asset-Backed Securities, at Carrying Value		0
Agency backed securities, Fair Value Disclosure	0
Corporate notes and other	0	0
Total investment securities available-for-sale	0	0
Alternative investments	0	0
Other assets	0	0
Total assets at fair value	0	0
Liabilities at fair value [Abstract]
Other liabilities	0	0
Total liabilities at fair value	0	0
Fair Value, Measurements, Recurring [Member] | Models with Significant Observable Market Parameters (Level 2) [Member]
Assets, Fair Value Disclosure [Abstract]
U.S. treasury securities	30,445	250
U.S. government agency securities	180,801	21,769
Mortgage-backed securities	1,263,819	976,626
State and municipal securities	767,583	212,720
Asset-Backed Securities, at Carrying Value	173,292	78,580
Corporate notes and other	82,314	8,601
Total investment securities available-for-sale	2,498,254	1,298,546
Alternative investments	0	0
Other assets	11,812	13,340
Total assets at fair value	2,510,066	1,311,886
Liabilities at fair value [Abstract]
Other liabilities	13,886	15,758
Total liabilities at fair value	13,886	15,758
Fair Value, Measurements, Recurring [Member] | Models with Significant Unobservable Market Parameters (Level 3) [Member]
Assets, Fair Value Disclosure [Abstract]
U.S. treasury securities	0	0
U.S. government agency securities	0	0
Mortgage-backed securities	0	0
State and municipal securities	17,029	0
Asset-Backed Securities, at Carrying Value		0
Agency backed securities, Fair Value Disclosure	0
Corporate notes and other	0	0
Total investment securities available-for-sale	17,029	0
Alternative investments	28,874	10,478
Other assets	0	0
Total assets at fair value	45,903	10,478
Liabilities at fair value [Abstract]
Other liabilities	0	0
Total liabilities at fair value	0	0
Fair Value, Measurements, Nonrecurring [Member]
Assets and liabilities measured at fair value on a nonrecurring basis [Abstract]
Other real estate owned	27,831	6,090
Impaired Financing Receivable, with Related Allowance, Recorded Investment	55,138	26,506
Total	82,969	32,596
Total losses on other real estate owned	(203)	135
Total losses on collateral dependent nonaccrual loans, net	(722)	(7,173)
Total losses	(519)	(7,308)
Fair Value, Measurements, Nonrecurring [Member] | Quoted Market Prices in an Active Market (Level 1) [Member]
Assets and liabilities measured at fair value on a nonrecurring basis [Abstract]
Other real estate owned	0	0
Impaired Financing Receivable, with Related Allowance, Recorded Investment	0	0
Total	0	0
Fair Value, Measurements, Nonrecurring [Member] | Models with Significant Observable Market Parameters (Level 2) [Member]
Assets and liabilities measured at fair value on a nonrecurring basis [Abstract]
Other real estate owned	0	0
Impaired Financing Receivable, with Related Allowance, Recorded Investment	0	0
Total	0	0
Fair Value, Measurements, Nonrecurring [Member] | Models with Significant Unobservable Market Parameters (Level 3) [Member]
Assets and liabilities measured at fair value on a nonrecurring basis [Abstract]
Other real estate owned	27,831	6,090
Impaired Financing Receivable, with Related Allowance, Recorded Investment	55,138	26,506
Total	82,969	32,596
Other Assets [Member]
Assets measured on recurring basis, unobservable input reconciliation, calculation [Roll Forward]
Fair value, beginning of period	10,478	9,764
Total realized gains included in income	605	131
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	0	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Assets Acquired	17,062
Purchases	2,330	1,639
Issuances	0	0
Settlements	(1,601)	(1,056)
Transfers out of Level 3	0	0
Fair value, September 30	28,874	10,478
Total realized gains included in income related to financial assets and liabilities still on the consolidated balance sheet at period end	605	131
Available-for-sale Securities [Member]
Assets measured on recurring basis, unobservable input reconciliation, calculation [Roll Forward]
Fair value, beginning of period	0	0
Total realized gains included in income	66	0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	709	0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Assets Acquired	16,254
Purchases	0	0
Issuances	0	0
Settlements	0	0
Transfers out of Level 3	0	0
Fair value, September 30	17,029	0
Total realized gains included in income related to financial assets and liabilities still on the consolidated balance sheet at period end	$ 66	$ 0