Earnings Per Common Share Data (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Earnings Per Share Disclosure [Line Items]
Net earnings	$ 26,786	$ 21,707	$ 48,455	$ 48,128
Distributed Earnings	(11,696)	0	(23,720)	0
Undistributed Earnings, Basic	15,090	21,707	24,735	48,128
Percentage of Undistributed Earnings Allocated to Common Shares	98.30%	100.00%	98.30%	100.00%
Undistributed Earnings Allocated to Common Shares	14,833	21,707	24,315	48,128
Dividends, Common Stock, Cash	11,497	0	23,315	0
Net Income (Loss) Available to Common Stockholders	$ 26,330	$ 21,707	$ 47,630	$ 48,128
Weighted Average Number of Shares Outstanding, Basic	37,687	41,170	37,998	41,642
Incremental Common Shares Attributable to Participating Nonvested Shares with Non-forfeitable Dividend Rights	648	0	658	0
Weighted-average common shares outstanding, diluted	38,951	42,719	39,379	43,382
Earnings Per Share, Basic	$ 0.70	$ 0.53	$ 1.25	$ 1.16
Net earnings per common share, diluted	$ 0.68	$ 0.51	$ 1.21	$ 1.11
Incremental Common Shares Attributable to Share-based Payment Arrangements	1,264	1,549	1,381	1,740
Weighted Average Number of Shares Outstanding, Total	38,335	41,170	38,656	41,642
Anti-dilutive options excluded from calculation of weighted-average common shares outstanding, diluted	2,788	3,521	2,637	3,403

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Antidilution

-URI http://asc.fasb.org/extlink&oid=6505113

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Diluted Earnings Per Share

-URI http://asc.fasb.org/extlink&oid=6510752

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Contingent Stock Agreement

-URI http://asc.fasb.org/extlink&oid=6508534

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 260

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 128

-Paragraph 40

-Subparagraph c

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 128

-Paragraph 13, 14

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Emerging Issues Task Force (EITF)

-Number 07-4

-Paragraph 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 128

-Paragraph 171

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.