Fair Value Measurements - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
State tax credits, held for sale	$ 42,364	$ 43,468
State Tax Credits Held For Sale, Fair Value Disclosure	$ 350	400
State Tax Credit Term	10 years
Receivables, Fair Value Disclosure	$ 3,500
Impaired Financing Receivable, Related Allowance	600
Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
State tax credits, held for sale	42,400
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	350	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	42,000
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	41,072	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	$ 350	$ 400