Financial Instruments - Changes in Level 3 Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	$ 3,833	$ 0	$ 3,833	$ 0	$ 4,402	$ 3,653	$ 100	$ 100
Total Realized and Unrealized Gains (Losses)	569		(180)
Purchases and Issuances		100		100
Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	8,706	12,779	5,946	12,954
Total Realized and Unrealized Gains (Losses)	82	0	(87)	623
Purchases and Issuances	115	292	4,167	125
Sales and Settlements	(124)	2	(627)	(728)
Transfers In (Out)	0	(99)	(620)	0
Ending Balance	8,779	12,974	8,779	12,974
Interest Rate Lock Commitments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	3,038		2,375
Total Realized and Unrealized Gains (Losses)	7,490		8,153
Ending Balance	10,528		10,528
Auction Rate Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	85,025	72,553	85,124	72,118
Total Realized and Unrealized Gains (Losses)	(327)	498	(326)	(192)
Purchases and Issuances	10,975	6,175	14,175	10,425
Sales and Settlements	(3,125)	(1,150)	(6,425)	(4,275)
Ending Balance	92,548	78,076	92,548	78,076
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	1,514	2,329	1,514	2,329	2,205	2,600	2,094	2,647
Total Realized and Unrealized Gains (Losses)	691	(235)	1,086	318
Mortgage and Other Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance		52		40
Total Realized and Unrealized Gains (Losses)		7		14
Purchases and Issuances		50		73
Sales and Settlements		(36)		(54)
Transfers In (Out)		(6)		(6)
Ending Balance		67		67
Municipal Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	70	239	236	239
Total Realized and Unrealized Gains (Losses)	(18)	(3)	(184)	(3)
Purchases and Issuances		0		0
Sales and Settlements		0		0
Ending Balance	$ 52	$ 236	$ 52	$ 236