Stock-Based Compensation Plans (Schedule of Company's Stock Options Outstanding) (Details) - Stock Options [Member] $ / shares in Units, $ in Thousands	3 Months Ended
Mar. 31, 2018 USD ($) $ / shares shares
Number of shares:
Balance options outstanding, beginning	38,689
Granted
Exercised	(9,508)
Forfeited
Expired
Balance options outstanding, end	29,181
Exercisable, end of period	29,181
Weighted Average Exercise Price
Balance, beginning \| $ / shares	$ 16.09
Exercised \| $ / shares	16.60
Forfeited \| $ / shares
Expired \| $ / shares
Outstanding \| $ / shares	15.92
Exercisable \| $ / shares	$ 15.92
Weighted- Average Contractual Term (years), outstanding	6 months
Weighted- Average Contractual Term (years), exercisable	6 months
Aggregate Intrinsic Value, exercised \| $	$ 184,018
Aggregate Intrinsic Value, outstanding \| $	575,671
Aggregate Intrinsic Value, exercisable \| $	$ 575,671

The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.