Common Stock - Nonvested Restricted Shares (Detail) - $ / shares	3 Months Ended				12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Granted					$ 36.36	$ 52.85	$ 55.26
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Nonvested Restricted Shares, Beginning Balance	611,896	635,718	688,131	496,842	496,842
Nonvested Restricted Shares, Granted	3,038	3,368		347,398
Restricted Shares, Vested	(1,999)	(23,705)	(20,221)	(156,109)
Nonvested Restricted Shares, Forfeited	(21,519)	(3,485)	(32,192)
Nonvested Restricted Shares, Ending Balance	591,416	611,896	635,718	688,131	591,416	496,842
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Nonvested, Weighted Average Grant Date Fair Value, Beginning of Period	$ 44.70	$ 44.42	$ 44.90	$ 51.65	$ 51.65
Granted	55.45	55.02		35.98
Vested	52.75	37.37	42.32	46.50
Forfeited	47.46	53.34	53.91
Nonvested, Weighted Average Grant Date Fair Value, End of Period	$ 44.63	$ 44.70	$ 44.42	$ 44.90	$ 44.63	$ 51.65