Fair Value Measurements - Changes in Level 3 Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	$ 544	$ 4,402	$ 1,222	$ 3,653
Total Realized and Unrealized Gains (Losses)	678	(749)
Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	9,508	5,946
Total Realized and Unrealized Gains (Losses)	(231)	(169)
Purchases and Issuances	198	4,052
Sales and Settlements	(215)	(503)
Transfers In (Out)	(111)	(620)
Ending Balance	9,149	8,706
Interest Rate Lock Commitments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	7,576	2,375
Total Realized and Unrealized Gains (Losses)	3,848	663
Ending Balance	11,424	3,038
Auction Rate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	91,422	85,124
Total Realized and Unrealized Gains (Losses)	935	1
Purchases and Issuances	8,225	3,200
Sales and Settlements	(1,525)	(3,300)
Ending Balance	99,057	85,025
Auction Rate Securities Purchase Commitment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	797	2,205	902	2,600
Total Realized and Unrealized Gains (Losses)	105	395
Municipal Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	164	236
Total Realized and Unrealized Gains (Losses)	(60)	(166)
Ending Balance	$ 104	$ 70