[Line Items] for Schedule of Shareholders' Equity [Table]

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- Definition

Aggregate dividends declared during the period for each share of common stock outstanding.

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- Definition

Amount of stock repurchase plan authorized.

+ References

No definition available.

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- Definition

The number of shares authorized to be repurchased by an entity's Board of Directors under a stock repurchase plan.

+ References

No definition available.

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- Definition

Total cost of shares repurchased divided by the total number of shares repurchased.

+ References

Reference 1: 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

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- Definition

Number of shares that have been repurchased during the period and are being held in treasury.

+ References

Reference 1: 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

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-Topic 505
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- Definition

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

+ References

Reference 1: 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=84159872&loc=d3e21463-112644

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Stockholders' Equity (Details) - USD ($)			3 Months Ended		94 Months Ended	137 Months Ended	153 Months Ended
Stockholders' Equity (Details) - USD ($)	Nov. 07, 2017	May 16, 2017	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2018	Mar. 31, 2018	Jun. 02, 2016	May 24, 2016	May 19, 2015
Schedule of Shareholders' Equity [Line Items]
Stock repurchased during period (in shares)			133,695	198,928			12,446,723
Aggregate price of shares repurchased since inception			$ 4,938,613	$ 6,863,113			$ 165,525,566
Average price of shares repurchased since inception (per share)			$ 36.94	$ 34.50			$ 13.30
Dividend Declared
Schedule of Shareholders' Equity [Line Items]
Cash dividends declared per common share	$ 0.13	$ 0.13
2010 Stock Repurchase Program
Schedule of Shareholders' Equity [Line Items]
Stock repurchase program, authorized amount								$ 25,000,000	$ 25,000,000
Stock repurchase program amount authorized (in shares)								2,000,000.0		5,700,000.0
Stock repurchased during period (in shares)			0	6,100	3,843,495
Aggregate price of shares repurchased since inception			$ 0	$ 195,993	$ 61,232,115
Average price of shares repurchased since inception (per share)			$ 0.00	$ 32.13	$ 15.93
2005 401(k) Stock Repurchase Program
Schedule of Shareholders' Equity [Line Items]
Stock repurchased during period (in shares)			118,203	176,429			6,668,226
Aggregate price of shares repurchased since inception			$ 4,378,925	$ 6,107,515			$ 86,447,730
Average price of shares repurchased since inception (per share)			$ 37.05	$ 34.62			$ 12.96
2006 Director and Officer Repurchase Program
Schedule of Shareholders' Equity [Line Items]
Stock repurchased during period (in shares)			15,492	16,399		1,935,002
Aggregate price of shares repurchased since inception			$ 559,688	$ 559,605		$ 17,845,721
Average price of shares repurchased since inception (per share)			$ 36.13	$ 34.12		$ 9.22