Fair Value Measurements - Narrative (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016 USD ($) security	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) security	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
State tax credits held for sale, including $4,774 and $5,941 carried at fair value, respectively	$ 44,918		$ 44,918		$ 45,850
State tax credits, held for sale, carried at fair value	4,774		$ 4,774		5,941
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 $4,774 and $5,941 carried at fair value, respectively	44,900		$ 44,900
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, carried at fair value	$ 4,774		$ 4,774		5,941
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		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, carried at fair value	$ 40,100		$ 40,100
Estimated fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
State tax credits, held for sale, carried at fair value	49,961		49,961		49,588
Estimated fair value | Recurring basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
State tax credits, held for sale, carried at fair value	4,774		4,774		$ 5,941
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 gains (losses) relating to assets still held at the reporting date	$ 41	$ 36	$ (264)	$ 310
LIBOR | LIBOR Swap Curve [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate basis spread on variable rate	205.00%		205.00%
LIBOR Swap Curve [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate basis point spread			205