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Shareholders' Equity - Summary of Nonvested Share Activity (Detail) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards vested, Number of Shares	(4,897,965)
Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	11,810,781
Awards granted, Number of shares	8,050,800
Awards forfeited/waived, Number of Shares	(126,301)
Awards cancelled on failed vesting conditions, Number of Shares	(1,682,276)
Awards vested, Number of Shares	(4,897,965)
Ending Balance, Number of Shares	13,155,039	11,810,781
Employees [Member] | 2013 CEO Special Bonus [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	7,095
Awards vested, Number of Shares	(7,095)
Ending Balance, Number of Shares	0	7,095
Employees [Member] | Employee Plan 2014 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	1,611,453
Awards forfeited/waived, Number of Shares	(7,253)
Awards vested, Number of Shares	(1,604,200)
Ending Balance, Number of Shares		1,611,453
Employees [Member] | 2014 CEO Special Bonus [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	11,495
Awards vested, Number of Shares	(11,495)
Ending Balance, Number of Shares		11,495
Employees [Member] | Employee Plan 2015 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	3,170,739
Awards forfeited/waived, Number of Shares	(24,694)
Awards vested, Number of Shares	(1,515,261)
Ending Balance, Number of Shares	1,630,784	3,170,739
Employees [Member] | 2015 CEO Special Bonus [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	35,579
Awards vested, Number of Shares	(17,790)
Ending Balance, Number of Shares	17,789	35,579
Employees [Member] | Employee Plan 2016 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	6,974,420
Awards forfeited/waived, Number of Shares	(62,179)
Awards cancelled on failed vesting conditions, Number of Shares	(1,682,276)
Awards vested, Number of Shares	(1,717,119)
Ending Balance, Number of Shares	3,512,846	6,974,420
Employees [Member] | Employee Plan 2017 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted, Number of shares	7,981,635
Awards forfeited/waived, Number of Shares	(32,175)
Awards vested, Number of Shares	(1,950)
Ending Balance, Number of Shares	7,947,510
Employees [Member] | 2016 CEO Special Bonus [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted, Number of shares	69,165
Awards vested, Number of Shares	(23,055)
Ending Balance, Number of Shares	46,110
Supervisory Board [Member] | 2006 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares		3,000
Year of grant	2006
Exercised		(3,000)
Supervisory Board [Member] | 2007 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	7,500	19,500
Year of grant	2007
Exercised	(7,500)	(12,000)
Ending Balance, Number of Shares		7,500
Supervisory Board [Member] | 2008 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	24,000	39,000
Year of grant	2008
Exercised	(7,500)	(15,000)
Ending Balance, Number of Shares	16,500	24,000
Supervisory Board [Member] | 2009 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	35,000	45,000
Year of grant	2009
Exercised	(12,500)	(10,000)
Ending Balance, Number of Shares	22,500	35,000
Supervisory Board [Member] | 2010 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	45,000	45,000
Year of grant	2010
Exercised	(15,000)
Ending Balance, Number of Shares	30,000	45,000
Supervisory Board [Member] | 2011 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	67,500	82,500
Year of grant	2011
Exercised	(15,000)	(15,000)
Ending Balance, Number of Shares	52,500	67,500
Supervisory Board [Member] | 2012 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	87,500	95,000
Year of grant	2012
Exercised	(22,500)	(7,500)
Ending Balance, Number of Shares	65,000	87,500

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Share based compensation arrangement by share based payment award equity instruments other than options cancelled on failed vesting conditions in period.

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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(2)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Number of non-option equity instruments exercised by participants.

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-Name Accounting Standards Codification
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-SubTopic 10
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-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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