Stockholders' Equity - Reconciliation of Beginning and End of Period Equity Accounts (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 1,185,756
Net income	8,983	$ 29,381
Other comprehensive income	30,521	$ 21,008
Share repurchase program	(15,565)
Stock compensation plans	(335)
Cash dividends - $0.105 per share	(5,334)
Dividend paid to noncontrolling shareholder	0
Ending Balance	$ 1,204,026
Cash dividends per share (in dollars per share)	$ 0.105	$ 0.105
Total Parent Stockholders’ Equity
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 1,127,096
Net income	8,285
Other comprehensive income	26,576
Share repurchase program	(15,565)
Stock compensation plans	(335)
Cash dividends - $0.105 per share	(5,334)
Dividend paid to noncontrolling shareholder	0
Ending Balance	1,140,723
Noncontrolling Shareholders’ Interests in Consolidated Subsidiary
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	58,660
Net income	698
Other comprehensive income	3,945
Share repurchase program	0
Stock compensation plans	0
Cash dividends - $0.105 per share	0
Dividend paid to noncontrolling shareholder	0
Ending Balance	$ 63,303