Fair Value Measurements - Narrative (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
State tax credits, held for sale	$ 46,481	$ 43,468
State Tax Credits Held For Sale, Fair Value Disclosure	$ 299	400
State Tax Credit Term	10 years
Receivables, Fair Value Disclosure	$ 2,400
Impaired Financing Receivable, Related Allowance	900
Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
State tax credits, held for sale	46,500
Recurring basis | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
State Tax Credits Held For Sale, Fair Value Disclosure	299	400
Portion at Other than Fair Value, Fair Value Disclosure
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
State Tax Credits Held For Sale, Fair Value Disclosure	46,200
Estimated fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
State Tax Credits Held For Sale, Fair Value Disclosure	45,069	44,271
Estimated fair value | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
State Tax Credits Held For Sale, Fair Value Disclosure	$ 299	$ 400