Loans - Narrative Section (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Debt Instrument [Line Items]
Fees and cost related to loans	$ 4,500		$ 4,500		$ 6,300
Loans Held for Sale Included in Loans Receivable					14,400
Carrying amount of loan investments	3,120,543	$ 2,822,555	3,120,543	$ 2,822,555	2,860,921
Commercial Loan [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	1,807,883		1,807,883		1,560,430
Non Accrual [Member]
Debt Instrument [Line Items]
Recorded investment, non-accrual status	19,200		19,200
Increase (decrease) in non-accrual loans			$ 11,600
Percentage increase (decrease) in past due loans			37.60%
Non ASC 310-30 [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	2,994,947		$ 2,994,947		2,715,069
Allowance for Loan and Lease Losses, Write-offs	8,843	17,540	9,174	21,881
Non ASC 310-30 [Member] | Commercial Loan [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	1,776,008		1,776,008		1,521,150
ASC 310-30 [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	125,596		125,596		145,852
Allowance for Loan and Lease Losses, Write-offs		$ 6		$ 47
ASC 310-30 [Member] | Commercial Loan [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	31,875		31,875		39,280
Total Loans [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	3,120,543		3,120,543		2,860,921
Total Loans [Member] | Non ASC 310-30 [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	2,994,947		2,994,947		2,715,069
Recorded investment, non-accrual status	19,157		19,157		30,717
Total past due loans	13,457		13,457		19,435
Total Loans [Member] | Non ASC 310-30 [Member] | Commercial and Industrial [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	1,286,355		1,286,355		1,074,696
Recorded investment, non-accrual status	3,783		3,783		8,688
Total past due loans	2,308		2,308		8,221
Total Loans [Member] | Non ASC 310-30 [Member] | Energy Loans [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	81,351		81,351		90,273
Recorded investment, non-accrual status	3,551		3,551		12,645
Total past due loans	3,551		3,551		6,550
Total Loans [Member] | Non ASC 310-30 [Member] | Commercial Loan [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	1,776,008		1,776,008		1,521,150
Recorded investment, non-accrual status	12,272		12,272		25,294
Total past due loans	8,894		8,894		16,127
Total Loans [Member] | Non ASC 310-30 [Member] | Owner-Occupied [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	276,155		276,155		221,544
Recorded investment, non-accrual status	2,829		2,829		2,056
Total past due loans	2,289		2,289		855
Total Loans [Member] | Non ASC 310-30 [Member] | Non Owner-Occupied [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	325,574		325,574		309,068
Recorded investment, non-accrual status	607		607		66
Total past due loans	653		653		28
Total Loans [Member] | ASC 310-30 [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	125,596		125,596		145,852
Total Loans [Member] | ASC 310-30 [Member] | Commercial Loan [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	31,875		31,875		39,280
Total Loans [Member] | Substandard [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	72,045		72,045		116,558
Total Loans [Member] | Substandard [Member] | Non ASC 310-30 [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	37,199		37,199		56,924
Total Loans [Member] | Substandard [Member] | Non ASC 310-30 [Member] | Commercial and Industrial [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	15,092		15,092		25,636
Total Loans [Member] | Substandard [Member] | Non ASC 310-30 [Member] | Energy Loans [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	3,551		3,551		7,811
Total Loans [Member] | Substandard [Member] | Non ASC 310-30 [Member] | Commercial Loan [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	26,644		26,644		45,490
Total Loans [Member] | Substandard [Member] | Non ASC 310-30 [Member] | Owner-Occupied [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	5,925		5,925		10,137
Total Loans [Member] | Substandard [Member] | Non ASC 310-30 [Member] | Non Owner-Occupied [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	1,488		1,488		2,251
Total Loans [Member] | Substandard [Member] | ASC 310-30 [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	34,846		34,846		59,634
Total Loans [Member] | Substandard [Member] | ASC 310-30 [Member] | Commercial Loan [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	6,044		6,044		11,234
Total Loans [Member] | Special Mention [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	58,250		58,250		38,590
Total Loans [Member] | Special Mention [Member] | Non ASC 310-30 [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	54,947		54,947		35,669
Total Loans [Member] | Special Mention [Member] | Non ASC 310-30 [Member] | Commercial and Industrial [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	10,968		10,968		7,243
Total Loans [Member] | Special Mention [Member] | Non ASC 310-30 [Member] | Energy Loans [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	2,444		2,444
Total Loans [Member] | Special Mention [Member] | Non ASC 310-30 [Member] | Commercial Loan [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	51,772		51,772		25,536
Total Loans [Member] | Special Mention [Member] | Non ASC 310-30 [Member] | Owner-Occupied [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	17,154		17,154		9,371
Total Loans [Member] | Special Mention [Member] | Non ASC 310-30 [Member] | Non Owner-Occupied [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	2,926		2,926		5,895
Total Loans [Member] | Special Mention [Member] | ASC 310-30 [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	3,303		3,303		2,921
Total Loans [Member] | Special Mention [Member] | ASC 310-30 [Member] | Commercial Loan [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	1,125		1,125		610
Total Loans [Member] | Doubtful [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	1,071		1,071		9,113
Total Loans [Member] | Doubtful [Member] | Non ASC 310-30 [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	1,071		1,071		5,345
Total Loans [Member] | Doubtful [Member] | Non ASC 310-30 [Member] | Commercial and Industrial [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	615		615		491
Total Loans [Member] | Doubtful [Member] | Non ASC 310-30 [Member] | Energy Loans [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments					4,843
Total Loans [Member] | Doubtful [Member] | Non ASC 310-30 [Member] | Commercial Loan [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	908		908		5,334
Total Loans [Member] | Doubtful [Member] | Non ASC 310-30 [Member] | Owner-Occupied [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments	$ 260		$ 260
Total Loans [Member] | Doubtful [Member] | ASC 310-30 [Member]
Debt Instrument [Line Items]
Carrying amount of loan investments					$ 3,768