Common Stock - Share Repurchase of Common Stock (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended	252 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014
Statement Of Stockholders Equity [Abstract]
Aggregate Purchase Price	$ 567,544	$ 554,491	$ 227,281	$ 5,876,000
Number of Shares Repurchased	508us-gaap_TreasuryStockSharesAcquired	581us-gaap_TreasuryStockSharesAcquired	286us-gaap_TreasuryStockSharesAcquired	23,800us-gaap_TreasuryStockSharesAcquired

Equity impact of the cost of common and preferred stock that were repurchased during the period. Recorded using the cost method.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.3-04)

-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 30

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6405813&loc=d3e23239-112655

Name:	us-gaap_TreasuryStockValueAcquiredCostMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration