Summary of Restricted Stock Award Activity (Detail) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of restricted stock unit awards that vested during the period	242,945
Fair value of restricted shares that vested during the period	$ 7,815	$ 8,091
Compensation expense recognized during the period	4,798	4,294
Income tax benefit recognized upon vesting of restricted stock awards	$ 1,751	$ 2,633
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of restricted stock unit awards that vested during the period	127,084	97,115
Fair value of restricted shares that vested during the period	$ 4,846	$ 4,155
Accumulated dividends paid upon vesting of restricted stock unit awards	501	313
Compensation expense recognized during the period	2,080	2,150
Income tax benefit recognized upon vesting of restricted stock awards	$ 740	$ 1,745

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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Cash outflow in the form of capital distributions and dividends to common shareholders, preferred shareholders and noncontrolling interests.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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