Fair Value Measurements - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) security	Dec. 31, 2014 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
State tax credits, held for sale, including $5,941 and $11,689 carried at fair value, respectively	$ 45,850	$ 38,309
State Tax Credits Held For Sale, Fair Value Disclosure	$ 5,941	11,689
State tax credit term	10 years
Years of tax credits generated	10 years
Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
State tax credits, held for sale, including $5,941 and $11,689 carried at fair value, respectively	$ 45,900
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	$ 5,941	11,689
Auction Rate Securities | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of available-for-sale securities | security	3
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	$ 39,900
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	49,588	42,970
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	5,941	11,689
State tax credits held for sale, at fair value | Recurring basis | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in unrealized (losses) gains relating to assets still held at the reporting date	$ (1,212)	$ 868
Minimum | State tax credits held for sale, at fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	2.30%
Maximum | State tax credits held for sale, at fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	4.82%
LIBOR | LIBOR Swap Curve
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate basis point spread	2.05
Discount rate basis spread on variable rate	205.00%	205.00%
Lower range of basis spread on variable rate	265.00%
Higher range of basis spread on variable rate	285.00%
Prime Rate | State tax credits held for sale, at fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate basis spread on variable rate	75.00%