Loans Loans Changes in the Allowance for Loan Losses by Oil and Gas Segment (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 238,023	$ 265,880
Charge offs	(57,560)	(50,536)
Recoveries	16,462	20,179
Net Charge offs	(41,098)	(30,358)
Provision for loan losses	17,500	2,500
Balance at end of period	214,425	238,023
Allowance for loan losses
Individually evaluated for impairment			$ 23,291	$ 15,304
Collectively evaluated for impairment			191,133	222,719
Total allowance for loan losses	214,425	265,880	214,425	238,023
Loans
Individually evaluated for impairment			119,925	133,690
Collectively evaluated for impairment			22,633,075	22,801,887
Total loans			22,754,710	22,940,429
Oil and Gas
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	12,000	27,000
Charge offs	(39,000)	(24,000)
Recoveries	5,000	6,000
Net Charge offs	(34,000)	(17,000)
Provision for loan losses	44,000	2,000
Balance at end of period	21,000	12,000
Allowance for loan losses
Individually evaluated for impairment			11,000	0
Collectively evaluated for impairment			10,000	12,000
Total allowance for loan losses	$ 21,000	$ 12,000	21,000	12,000
Loans
Individually evaluated for impairment			36,000	22,000
Collectively evaluated for impairment			545,000	725,000
Total loans			$ 582,000	$ 747,000